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CTask A Multitasking Kernel for C Version 2.2 Released 90-10-12 Public Domain Software written by Thomas Wagner Ferrari electronic GmbH Contents About this Manual 1 Introduction 2 An Example 2 Switching the Context 2 You have Mail 3 Reentrancy and Resources 3 DOS Access 4 Handling the Keyboard 4 Serial I/O and Timeouts 5 Priorities 5 Change to your liking 5 General Notes 7 What can CTask NOT be used for? 7 What is required to use CTask? 7 Do I have to pay for using CTask? 8 What support can I expect? 9 About this Release 10 Multitasking Basics 11 Tasks 11 Events 11 Reentrancy 12 Deadlocks 13 Using CTask 15 Configuration Options 15 Memory Allocation 21 Snapshot 21 Task Stacks 22 Drivers 22 Things to remember 23 Priority Handling 23 Multitasking and DOS 25 Spawning and CTask TSR's 26 Task Groups 27 How does CTask work 29 Queues 29 The Scheduler 30 Events 30 Resources 30 Flags 31 Counters 31 Mailboxes and Pipes 31 Serial and Printer Drivers 32 Ctask Manual - Version 2.2 - 90-10-12 - Contents 1 CTask Data Types 34 Other definitions 35 Typedefs used for simplified type specifications 36 Error return values for event wait functions 37 Queues 37 The timer/watch/hotkey control block 38 The name link structure 43 The task control block structure 43 Task states 46 Task flags 47 The Group Control Block 48 The event control blocks 49 The Ticker structure 49 The flag event structure 50 The counter event structure 50 The resource event structure 51 The mailbox event structure 51 The pipe and word pipe event structure 51 The buffer event structure 52 The call chain structure 53 CTask Routines 54 Global Variables 54 Installation and Removal 54 Searching for names 57 Adding names 58 Remove Functions 58 Preemption and Scheduling 59 Miscellaneous 60 Task Operations 62 Timer Operations 64 Event wait Timeouts 65 "Tickers" 65 Delays 66 Timed Events, Watch Events, and Hotkeys 66 Event Operations 75 Resources 75 Flags 77 Counters 79 Mailboxes 81 Pipes 83 Buffers 86 The Keyboard Handler 88 The Serial I/O handler 88 The Printer Output Driver 94 Support Modules 96 Memory Allocation Interface 96 Printf replacements 97 Snapshot Dump 100 Ctask Manual - Version 2.2 - 90-10-12 - Contents 2 Advanced Topics 101 Primary and Secondary Kernels 101 TSR, Spawning, and EMS 104 Functions called by Kernel Routines 105 Some notes on potential trouble spots 107 Turbo C console output 107 The timer tick EOI 107 Debugging 108 Changes from Previous Versions 109 Changes for CTask 2.1 to 2.2 109 Version 2.2 Interface Changes 111 Changes for CTask 2.0 to 2.1 112 Version 2.1 Interface Changes 115 Changes for CTask 1.2 to 2.0 116 Version 2.0 Interface Changes 116 Changes for CTask 1.1b to 1.2 118 Changes for CTask 1.1 to 1.1b 120 Changes for CTask 0.1 to 1.1 120 Ctask Manual - Version 2.2 - 90-10-12 - Contents 3 About this Manual If you are new to CTask, I would suggest reading all chapters before attempting to build your first application. One chapter you can skip is the CTask Data Types section, since you are not required to know about the innards of CTask's structures. You can also ignore the List of Changes. If you are updating from version 2.0, read the List of Changes, and the new Advanced Topics section. The chapters on Data Types and Routines, and the Using CTask section, also contain new information. All other chapters are basically unchanged. Version 2.1 users will find little new information here. The changes in the data structures, and the new routines, are reflected here, but if you're short on paper, it should be sufficient to print just the list of changes. If you are updating from an older release, the List of Changes at the end is for you. You can safely skip the Introduction, and the section on Multitasking Basics. In the General Notes, you should read the section on support and the info about this release. In the Using CTask section, check the new configuration options, and the chapter on Memory Allocation. Check the Routine descriptions, and, if you are using internal data structures directly, the Data Type descriptions, for changes. The Advanced Topics section is new. Finally, a note to German speaking readers: Dieses Handbuch, wie auch die Kommentare im Quellcode, ist in Englisch abgefaßt, da dies die universelle Sprache für Computer- benutzer weltweit ist. Es gibt keine deutsche Version, und es wird voraussichtlich auch keine geben (sofern nicht jemand bereit ist einen angemessenen Betrag für eine Übersetzung auf den Tisch des Hauses zu legen). Selbstverständlich bleibt es Ihnen unbenommen, das Handbuch selbst zu übersetzen und diese Version auch zu vertreiben, oder mir zum Vertrieb anzubieten. Wie die Software ist auch dieses Handbuch Public Domain. Ctask Manual - Version 2.2 - 90-10-12 - Page 1 Introduction CTask is a set of routines that allow your C program to execute functions in parallel, without you having to build in sophisti- cated polling and switching schemes. CTask handles the switching of processor time with a priority based, preemptive scheduler, and provides a fairly complete set of routines for inter-task communication, event signalling, and task interlocking. CTask also includes a number of drivers for MS-DOS that build on the basic functions to allow you to include serial I/O, printer buffering, and concurrent access to DOS functions into your programs with little programming effort. An Example To illustrate one possible use of CTask, let me elaborate on the following example. Say you just finished your nifty telecommuni- cations program, complete with download protocols, scripts, and everything. But wouldn't it be nice to be able to print the file you just downloaded while receiving the next, and edit a comment to some previous message without interrupting the transmission? So you take those editor routines from a previous project, plug them in, and - oops, how do you switch back and forth between editing, communication and printing? The answer to this is CTask. CTask allows your C program to do many different things at the same time by switching the processor between the tasks you de- fine. And since most of the time your program is waiting for some slow device (like the human hand) to provide feedback, this switching is completely transparent, and will not noticeably slow your program down. Switching the Context So what is needed to allow the user to edit a file while at the same time downloading another and printing a third? First, you have to have some form of "context switching". This means that you have to be able to interrupt the processing of the download when the user presses a key, process the key, and return to the download "task" at the exact same point it was interrupted. One solution to this would be to include a poll for the keyboard at several points in the download routine, and call the editor task when a key is available. But apart from cluttering your code with lots of unrelated calls, there is another problem. What if the operation the user requested is more involved than just putting the character on the screen, like writing the file to disk? This might take so long that your download times out. There must be a way to pass control back and forth between the two tasks, such that no task is delayed for an extended period of time, and also to activate the print spooler task at some defined interval to output the data to the printer. This context switching is called "scheduling" in CTask. The "scheduler" is Ctask Manual - Version 2.2 - 90-10-12 - Page 2 invoked on every system timer tick, and will save the context of the current task. The scheduler then takes the first element from the queue of tasks that are eligible to be run, and restores the context of this task, returning to the point where the task was interrupted. This switching is completely automatic, and requires no special programming in the tasks itself. All you have to do is to tell CTask that there are three tasks, the download task, the spooler task, and the editor task. You have Mail All you have to do for context switching, that is. There's a bit more to multitasking than meets the eye. How do you tell the spooler task what files to spool, and the download task what files to download? You can't call a task like an ordinary func- tion, so what you need for this is "inter-task communication". There must be a way to pass a message containing the filename to be printed to the spooler task, and there are several in CTask, one of them the "mailbox". The spooler can use a CTask call, wait_mail, to wait for a message to arrive at its mailbox. As long as nothing arrives, the spooler task will no longer be scheduled, so if there is nothing to print, it will not use any processor time. When you send a message with send_mail to the mailbox, the spooler will wake up, and process the file. You can also send more file name messages to the spooler while it still prints a file, leaving the messages in the mailbox until the spooler is ready to process the next file. Reentrancy and Resources This last example seems innocent enough, but there's a big stumb- ling block hidden in it. You allocate the file name messages in the controlling task with malloc, and you free them in the spooler with free, no problem, right? Wrong, there is a big problem, "reentrancy". Reentrancy means that you can re-enter a routine while another task is already using it, and that this will not disturb the operation of the interrupted task. But malloc and free share and modify global data, the chain of free memory blocks. Imagine the following: You just called malloc from the controlling task. Malloc has loaded the address of a free element into a local variable, and is about to write back the pointer to the next free element into the last. At exactly this moment, the timer ticks, and the spooler is activated. It has just finished printing, so it calls free. Free steps through the chain of free blocks to find the right place to insert the block. According to Murphy's law, it will find just the place where malloc is about to write back the pointer. Free coerces the elements, points the next pointer to the element malloc just wants to take off the chain, and returns. Malloc writes its next pointer into the middle of the newly coerced block, and now re- turns an element which is still in the free list. Compared to the Ctask Manual - Version 2.2 - 90-10-12 - Page 3 job of finding this kind of bug, stepping in for Tantalus may feel like a vacation. This kind of problem code is called a "critical region". There must be a way to make sure that no two tasks simultaneously enter such a region, and, you guessed it, CTask provides one, the "resource". When you request a resource in one task, all other tasks trying to request the same resource after that are put to sleep until you call release_resource. Only then will the highest priority task that waits for the resource wake up, and get access to the protected region. So you would have to substitute malloc and free calls in your routines with calls to functions that first request a resource, execute the function, and then release the resource. DOS Access But, you might ask, isn't there another reentrancy problem in this example, since both the spooler and the download task might simultaneously call DOS to do their file-I/O, and DOS is not reentrant? Do I have to substitute all my calls to fread and fwrite, too? The answer to this, luckily, is no. CTask traps all your DOS calls, and automatically encloses them in the necessary resource request and release calls, so you don't have to worry about trashing your disk by simultaneous DOS requests. The limited multitasking capabilities of DOS are exploited to allow some parallel processing in DOS, and CTask will also detect and handle DOS calls by resident background programs like the DOS PRINT utility. Handling the Keyboard CTask also allows you to circumvent DOS for keyboard input, so that waiting for the keyboard will not block other tasks from access to DOS functions. Previous versions of CTask used a "pipe" to store all keyboard input. Starting with version 1.2, CTask uses a "flag" to signal that keyboard input might be available. A "flag" is another form of inter-task communication that just sig- nals that some event occurred, without passing any specific data. The reason for using flags in the keyboard handler is compati- bility to TSR's. If a keyboard interrupt occurs, the interrupt handler just sets a flag, and passes on the interrupt. The key- board routines wait for this flag to be set, and then check the keyboard buffer if a character has arrived. If the keyboard buf- fer is empty, the flag is again cleared, and the keyboard rou- tines put the waiting task to sleep again, so the processor is free to do more interesting things than to loop waiting for the user to press a key. Ctask Manual - Version 2.2 - 90-10-12 - Page 4 Serial I/O and Timeouts The "pipe" is similar to the mailbox in that you can wait for items to be sent to a pipe. But unlike mailboxes, pipes use their own buffer to store the items (which are limited to bytes and words), so you don't have to allocate mail blocks for each item. When waiting on the pipe, your task is put to sleep, freeing the processor. Pipes are used for the serial I/O handler included with CTask that makes some of the work you've put into your communications package obsolete. When outputting data to the serial port via the CTask routines, the data is buffered in a pipe, and incoming data is also placed in a pipe. All interrupt handling, and the processing of modem status and XON/XOFF proto- cols, is done by CTask, so you can concentrate on implementing the higher level protocols. Since CTask allows all calls that wait for pipes, mail, and other events, to specify a timeout that is based on the system tick, you do not have to resort to timed waiting loops to detect communication line faults. You simply give a time limit on the wait call, and if that limit expires, the wait routine will return with an error indication. Priorities If the protocol you implement requires fast responses to incoming blocks, you can influence the response of CTask to your comm task's needs by giving this task a higher priority. CTask allows 65535 different priority levels, and tasks having higher priority are scheduled before tasks with lower priority. Also, high prio- rity tasks will get access to mail, pipes, and resources, before other tasks. It might even be sensible to split the comm task into two separate tasks, one of high priority that assembles the incoming bytes into blocks and handles the protocol, and a lower priority task that reads the received blocks from a mailbox and stores them on the disk. In extremely time critical applications, you can even turn off task preemption, so the timer tick will no longer cause a task switch. Change to your liking CTask provides all basic building blocks for implementing concurrent programs in an easy and comprehensible way. Since CTask is mainly implemented in C, it may not be the fastest possible system, but due to the straightforward design which uses few shortcuts, modifying the sources to suit your needs and taste can be done without weeks of studying assembler code that squeezes every microsecond from the processor. CTask is public domain code, and there are no restrictions on its use. It is distributed in source form, so you are free to change all aspects of the package. Multitasking programs, especially in embedded applications, tend to be very diverse in their needs for specific constructs. So although CTask is ready to run under DOS, and is Ctask Manual - Version 2.2 - 90-10-12 - Page 5 easily adaptable for embedded applications, you should see CTask more as a starting point for your own thoughts, and as a toolbox from which you can pick the instruments you need, than as a finished and fixed block of code you simply plug into your application. Ctask Manual - Version 2.2 - 90-10-12 - Page 6 General Notes What can CTask NOT be used for? CTask is not intended to provide for multitasking on the command level of MS-DOS. Although version 1.2 of CTask added the ability to TSR and spawn other programs, and to communicate between multiple copies of CTask, a full DOS-process management (which would have to include keeping track of memory allocation and DOS process control blocks) is not included. Adding this functio- nality would not be trivial (although certainly worthwhile). CTask also is not a true "Real-Time" multitasking system. Due to the completely dynamic structure of tasks and events, and the minimal restrictions on what interrupt handlers may do, it is nearly impossible to calculate a maximum interrupt or task switch latency. If you have critical timing requirements, you should consider getting a professional package like AMX. CTask has been used successfully in embedded control applications, and if your timing requirements are not that critical, or you're ready to take up the task of measuring and calculating latencies with your specific task setup, CTask may be useful even for Real-Time applications. However, you're more or less on your own in this field. And, there is no warranty that CTask does perform without errors, or does exactly what you or I intended. So CTask should not be used in applications in which malfunction of routines of this package would result in damage to property or health of any person without *very* extensive testing under all kinds of loads. In using CTask, you do so at your own risk. I have tested CTask extensively, but with a complex system like CTask, where timing might make a big difference, you can't be completely sure that all will work as intended. What is required to use CTask? To compile CTask, Microsoft C 5.1 or later, or Turbo C 2.0 or later are required. Microsoft MASM 5.1 or later, or TASM 1.01 or later is required for the assembler parts. Conversion to other compilers is possible if they conform to the new ANSI standard. Conversion of the assembler parts to other Assembler versions will likely be more complicated, since it requires substitution of the simplified model directives by explicit segment definitions, and adding the DGROUP to offsets referencing data. Note that you can not use TASM 1.0 to assemble CTask routines. The first version of TASM was not fully compatible with MASM, and creates different code in some places, which will lead to fatal crashes. TASM version 1.01 does not have this problem, and can safely be used. Ctask Manual - Version 2.2 - 90-10-12 - Page 7 The CTask modules have been compiled and tested with Microsoft C 6.0 without any apparent problems (Optimization level tested was /Ox). Since the stability of the MSC 6.0 code generator is doubtful, the distributed library was compiled with MSC 5.1. CTask will add 14k-25k of code to your program, depending on options and installed drivers. The minimum static data used by CTask is approximately 4k. Non-DOS versions use less memory. Converting CTask for stand-alone operation requires few changes. Mainly, the timer interrupt handler (in "tsktim.asm") has to be rewritten, and the initialization code (in "tskmain.c") may have to be changed. Changes to other modules (naturally except the optional hardware drivers) should not be necessary. The "DOS" and "IBM" configuration flags in tskconf.h can be disabled to elimi- nate most system-dependent features of CTask. Another requirement is a good debugger. If you never before wrote multitasking applications, you're in for some surprises. The nor- mal debugging tools (Symdeb, Codeview) are of only limited use, since they use DOS calls for their I/O, and thus may conflict with your background tasks. One safety measure is to first thor- oughly test your program with preemption disabled, possibly inserting some schedule() calls, and only allow task preemption if you found most major bugs. I personally recommend Periscope for debugging, since it can be made resident and so is always available, and because it does not use DOS. Periscope IV is the most expensive solution, and the best tool you can imagine, but the less costly versions will also help a lot. Do I have to pay for using CTask? No. One reason for writing CTask was to provide a free, no strings attached, utility, instead of the usual "for personal use only" restriction. Writing a multitasking application for personal use only doesn't seem too interesting to me. CTask is completely free, and there is no restriction on its use. You may incorporate all or parts of CTask in your programs, and redistri- bute it in source or binary form by any means. I also do not restrict the use of CTask in commercial applications. Since trying to distribute the unmodified CTask for money will only give you a bad name, you may even do that if you find someone dumb enough to buy it. Naturally, if you make a bundle from it, or simply like CTask, I would not reject a donation. However, this is not required, and it will not give you any special support. Ctask Manual - Version 2.2 - 90-10-12 - Page 8 What support can I expect? I will try my best to eliminate any bugs reported to me, and to incorporate suggested enhancements and changes. However, my spare time is limited, so I can not guarantee continued or individual support. (But since I'm one of the owners of a consulting firm, you can always hire me to do it...). Please address all reports or questions to my business address: Ferrari electronic GmbH attn: Thomas Wagner Beusselstrasse 27 D-1000 Berlin 21, Germany Phone: (+49 30) 396 50 21 Fax: (+49 30) 396 80 20 BIX: twagner UUCP: oeschi@netmbx.UUCP (attn: Thomas Wagner) But, please, if at all possible, do it in writing. Please do not phone unless it is absolutely vital (or you have a business proposal). I like to hear about any applications for CTask, and if you are visiting Berlin, I also invite you to drop by for a talk. But I am usually not that happy when I am interrupted in my paid work by a phone call requesting support for a free product. I will try to answer all letters and Faxes I receive. However, I am usually not the fastest in this respect, so please be patient. If you don't hear for me for a while, send me a short reminder. The same goes for UUCP E-mail, since I'm not directly connected. The preferred, and the fastest, method to reach me is through BIX. BIX (tm) is the BYTE Information Exchange, an electronic confe- rencing system created by McGraw-Hill, the publishers of the well renowned BYTE magazine. BIX can be (and is) accessed from all parts of the world. Although accessing BIX from outside the US isn't exactly cheap (don't ask me what I have to pay each month), the wealth of information available there, and the fast and extensive help the other members can give you on all kinds of hard- and software problems, makes it worth every Mark, Peseta, Franc, or Ruble you have to spend. New versions and updates of CTask will first appear on BIX. At the time of this writing, I am one of the moderators of the IBM exchange on BIX, moderating the "ibm.other" conference. I have created a support topic for CTask, where all suggested enhancements and changes, plus bug reports, can be posted. Just join "ibm.other", topic "ctask". You can also report problems of limited general interest via BIXmail to "twagner". Unless I am not able to reach the keyboard for some reason, I log on at least Ctask Manual - Version 2.2 - 90-10-12 - Page 9 once per day, so you can expect relatively fast responses to your queries. To get more info on joining BIX, call the BIX Customer Service at 800-227-2983 (U.S. and Canada), or 603-924-7681 (New Hampshire and outside the U.S.) from 8:30 to 23:00 Eastern Time (-5 GMT). BIX access currently is $39 for three months (flat fee, no extra charges for connect time), plus the applicable telecomm charges (Tymnet in the U.S. and Canada, your local PTT's Packet Net charges from outside the U.S.). If you're calling from the US, you can subscribe by dialling BIX direct at 617-861-9767. Hit the return key, and enter "bix" at the 'login (enter "bix")' prompt. At the 'Name?' prompt, enter "bix.flatfee". International users living near a BT Tymnet node can access BIX through international Tymnet at special low rates. Call the BIX helpline for Tymnet access points and charges. Other international users will need an account (NUI) with their local packet net. Please enquire at your post/telecomm office for details. If you already own a NUI, enter the BIX international network address (NUA), "310690157800", and enter "bix.flatfee" at the 'Name?' prompt. About this Release Since the Beta release of CTask in March 1988, CTask has found widespread distribution through several channels. I have heard from some users, and their suggestions have been implemented in this version as far as possible. Special thanks go to Kent J. Quirk, Peter Heinrich, Stephen Worthington, Burt Bicksler, Tron Hvaring, Joe Urso, Dave Goodwin, Chris Blum, and Dan Heine, for their bug reports, suggestions, and enhancements. Bug reports and suggestions also came in from others, thanks to all who wrote or called. The serial code in TSKSIO.C was enhanced for version 2.0 by S. Worthington, and his ideas on debugging have been incorporated in the version 2.1 debugging mode. Dan Heine provided valuable info on 80x87 numeric coprocessor support. Chris Blum wrote the integer-based millisecond to clock-tick conversion routine. Again, please notify me of your CTask application, report bugs, or suggest changes and enhancements. If I know you're using CTask, I can notify you of possible new releases and of possible severe bugs. Ctask Manual - Version 2.2 - 90-10-12 - Page 10 Multitasking Basics Tasks In CTask, a "task" is defined as a (far) C function. The number of tasks is not limited, and one function may be used for several tasks. There is little difference between a task function and a normal function. The usual form of a task function is void Taskfunc my_task (farptr arg) { one-time initialization code while (TRUE) { processing code } } A task function is (usually) never called directly. Rather, it is specified in the call to the create_task routine, and started by start_task. It will then continue to run, sharing the processor time with all other tasks, until it is "killed" by kill_task. Returning from the routine will have the same effect as a kill. The sharing of processor time is accomplished by "preempting" the tasks. Preemption means that the task is interrupted in the middle of some statement by a hardware interrupt (usually the timer), and is *not* immediately restarted when the interrupt handler returns. Instead, the next task that is able to run is activated by the "scheduler", with the interrupted task continuing its duty at some (normally unpredictable) later time. You can also have multi-tasking without preemption, and CTask supports this, too, but this requires full cooperation of all tasks in the system, such that no task continues to run for an extended period of time without passing control to other tasks by an explicit scheduling request, or by waiting for an event. The optional argument to the task function may be used if one function is to be used for more than one task, for example to pass a pointer to a static data area for use by this specific instance of the function. Events Tasks alone would be of limited use. If you have several routines which just do number crunching or sorting or such, making them into parallel tasks would be sensible only on a multiprocessor system. Normally, at least some of your tasks will wait for some outside "event" to happen, be it the user pressing a key, or a character arriving from the modem. Then there may be tasks which have to wait until another task finishes processing on some piece of data before they can continue. For this synchronization, there are a number of constructs in CTask, which I summarize under the Ctask Manual - Version 2.2 - 90-10-12 - Page 11 name "event". Common to all events are the operations of waiting for an event to happen, and signalling that the event has happened. Using a CTask event is much more efficient than looping while waiting on some shared data location to change state, and also eliminates concurrency problems inherent in such a simple approach. Tasks waiting for an event are taken off the scheduler queue, so they no longer use processor time. Reentrancy One of the biggest problem with multitasking in general, and C on the PC in particular, is reentrancy. Reentrancy means that you can use a routine, be it you own, or one of the C run-time library, from different tasks at the same time. When writing your own code, you can easily avoid problems, but when using the run- time library routines, you often can only guess if the routines are reentrant or not. A routine is NOT reentrant if it modifies static data. This can be illustrated by the following nonsense example: int non_reentrant (int val) { static int temp; temp = val; return temp * 2; } Now take two tasks, which call this routine. Task1 calls it with val=3, Task2 with val=7. What will be the return value for both tasks? You never know. There are three possible outcomes: 1) The tasks execute sequentially. Task1 will get 6, and Task2 14 as a result. This is what one normally expects. 2) Task1 runs up to "temp = val", then is interrupted by the timer. Task2 executes, and gets 14 as result. Then Task1 continues. Return for Task1 is 14. 3) Task2 runs up to "temp = val", then is interrupted by the timer. Task1 executes, and gets 6 as result. Then Task2 continues. Return for Task2 is 6. add to this the effects of optimization, and a loop, and the outcome is completely random. Most routines in the C library will not explicitly do something like this, but all functions that - do file I/O (read, write, printf, scanf, etc.) or - change memory allocation (malloc, free, etc.) Ctask Manual - Version 2.2 - 90-10-12 - Page 12 have to use some static data to do buffering, or to store the chain of memory blocks in. Interrupting such an operation may have disastrous effects. The most devilish aspect of non- reentrancy is that the effects are unpredictable. Your program may run 1000 times without any error, and then on the 1001th time crash the system so completely that only the big red switch will help. So what can you do about it? A lot. There are several ways to protect "critical regions" from being entered in parallel. The most simple method is to disable interrupts. This, however, should be used only for *very* short periods of time, and not for rou-tines that might themselves re-enable them (like file-I/O). A better method is to temporarily disable task preemption. The routines tsk_dis_preempt and tsk_ena_preempt allow this form of short-term task switch disable. Interrupts may still be processed, but tasks will not be preempted. The best way is to use a "resource". A resource is a special kind of event, which only one task can possess at a time. Requesting the resource before entering the routine, and releasing it afterwards, will protect you from any other task simultaneously entering the critical region (assuming that this task also requests the resource). It is also reasonably safe to use file-I/O without protection if it goes to different files. The C file control blocks for different files are distinct, so there will be no conflict between tasks. Since DOS access is automatically protected by CTask, concurrent file I/O is possible. What you may NEVER do is to use a non-reentrant routine that is not protected by an interrupt disable from an interrupt handler. An interrupt handler is not a task, and so can not safely request a resource or disable task preemption. This is the reason why the CTask routines generally disable interrupts before manipulating the internal queues rather than only disabling task preemption. Deadlocks One thing to watch out for when using resources or similar event mechanisms is not to get into a situation where Task 1 waits for a resource that Task 2 has requested, while at the same time Task 2 waits for a resource that Task 1 already has. This situation is called a deadlock (or, more picturesque, deadly embrace), and it can only be resolved with outside help (e.g. waking up one of the tasks forcibly). To illustrate, consider the following example: Ctask Manual - Version 2.2 - 90-10-12 - Page 13 void far task_1 () { ... request_resource (&rsc1, 0L); request_resource (&rsc2, 0L); ... } void far task_2 () { ... request_resource (&rsc2, 0L); request_resource (&rsc1, 0L); ... } Since interrupts are always enabled on return from a task switch, even if the statements are enclosed in a critical region, there is no guarantee that the request_resource calls will be executed without interruption. In this example, the problem is obvious, but in a more complex application, where resource requests or other waits might be buried in some nested routine, you should watch out for similar situations. One way to avoid problems would be in this example to change task_2 to void far task_2 () { int again; ... do { request_resource (&rsc2, 0L); if (again = c_request_resource (&rsc1)) { release_resource (&rsc2); delay (2L); } } while (again); ... } Note that this is only one of many possible approaches, and that this approach favors task_1 over task_2. You should also take care not to kill tasks that currently own a resource. CTask will not detect this, and the resource will never be freed. Ctask Manual - Version 2.2 - 90-10-12 - Page 14 Using CTask CTask comes archived with both source and binaries. The binary version is compiled in the large model, but since the precompiled kernel routines don't use any functions from the C library, you can use all functions in small or other model programs (except Turbo C's Tiny and Huge models). The include files provided specify all model dependencies, so you don't have to use the large model for your application, but always remember to include "tsk.h" for the type definitions and function prototypes. The C source files will work without changes for both Microsoft and Turbo C. The library files are not compatible, so use "ctaskms.lib" for Microsoft, and "ctasktc.lib" for Turbo C. In the distributed configuration (i.e. dynamic allocation of control blocks enabled), the file TSKALLOC.C must be added to the library or separately linked after compiling it *in the same model as the main program*. This file uses C-library routines, and thus must match the main program's memory model. The same goes for TSKSNAP.C, an optional snapshot-dump utility, and CONOUT.C, the sample console output handler. The provided "ctsupms.lib" and "ctsuptc.lib" files have been compiled in the large model, and may only be used with large model programs. Turbo C's huge model uses a different segment setup for data segments. This requires using a special data segment for all CTask data, and compilation of the CTask kernel in huge model. For the assembler files, the symbol TC_HUGE must be defined during assembly, the C files must be compiled with the Data- Segment and BSS-Segment naming options. Make-files for Turbo C Huge model are included. Configuration Options The file TSKCONF.H contains a number of #define's that allow you to configure some CTask features. In general, you should recompile all of CTask when changing one of the flags. Version 2.1 collects all configuration options for both Assembler and C in this file. The entries are CODE_SHARING If TRUE, the generated kernel supports code sharing. This requires the entry points to load DS on entry, and compi- lation with Large model (MSC) or Huge model (TC). This option is normally disabled (FALSE). Ctask Manual - Version 2.2 - 90-10-12 - Page 15 NEAR_CODE If TRUE, all CTask routines are 'near'. Use only with small or compact model. You will have to change the make-files so the compiler model is no longer Large, and the code segment is not named, when turning on this flag. The default is FALSE. Setting this option TRUE will save code, and make calls faster, but the library will no longer be model independent. This option is normally disabled (FALSE). LOCALS_FAR If TRUE, internal CTask routines ar 'far'. This might be necessary if your compiler/linker does not allow placing all CTask kernel code in a common segment. Do not set this flag if NEAR_CODE is set. This option is normally disabled (FALSE). CALL_PASCAL Use Pascal calling sequence for CTask routines. This may save some code, but may cause naming conflicts if your compiler limits external Pascal names to 8 characters. This option is normally disabled (FALSE). TC_HUGE (Assembler only) Define TC_HUGE for use with the Turbo C Huge model, and if it is desired to separate CTask's data from the normal data segment. This flag causes the CTASK_DATA segment to be defined, (class is DATA) and DS to be loaded with this segment on function entry. The C functions in the CTask kernel must be compiled to use the same data segment. This option is normally disabled (undefined). LOAD_DS (Assembler only) Define LOAD_DS to reload the data segment on entry to global functions. This flag must be defined for TC_HUGE. It can also be defined if the data segment can not safely be assumed to be loaded in DS on function entry, for example if the code sharing feature of version 2.1 is used. The C routines must be compiled with the necessary compiler switches or the _loadds keyword in this case. This option is normally disabled (undefined). Ctask Manual - Version 2.2 - 90-10-12 - Page 16 ROM_CODE (Assembler only) Define ROM_CODE TRUE for embedded systems using ROM-based code. This option disables storing variables in the code segment in some modules. Note that most DOS- related modules are not ROMable. This option is normally disabled (FALSE). FAR_STACK (Assembler only) Define FAR_STACK TRUE to save some space in the default DGROUP. With this define TRUE, the local stacks for the scheduler, the timer, and the interrupt handlers, are allocated in a separate segment. With Turbo C, you may have to edit the "c0.asm" startup module to accomodate the new segment. This option is normally disabled (FALSE). TSK_DYNAMIC If TRUE, you can let CTask dynamically create task and event control blocks, task stacks, and pipe buffers, by passing NULL as the block address. Since this requires the C runtime allocation calls, it is not suitable for non-DOS appli- cations (except if you provide your own memory allocation routines). This option is normally enabled (TRUE). TSK_DYNLOAD If FALSE, this instance of the kernel does not include dynamic allocation routines. Setting this flag to FALSE when TSK_DYNAMIC is TRUE only makes sense with multiple linked kernels. A resident kernel might not employ dynamic allocation, whereas a secondary kernel needs it. In this situation, TSK_DYNAMIC must be set in the primary so that the task kill code is included and the kernel configurations match, but TSK_DYNLOAD may be false to prevent inclusion of the malloc/free run-time routines. This option has no effect if TSK_DYNAMIC is FALSE. The default is TRUE. This option is normally enabled (TRUE). TSK_NAMEPAR If TRUE, all create_xxx calls accept an additional parameter, the name of the created control block. This name should contain only printeable characters, and should not be longer than 8 characters plus the zero terminator. This option is used together with TSK_NAMED (see below). This option is normally enabled (TRUE). It must be enabled for DOS. Ctask Manual - Version 2.2 - 90-10-12 - Page 17 TSK_NAMED If TRUE, all control blocks (except timer control blocks) are named and linked on creation. This allows the snapshot dump routine to display the system state, and also allows linking to control blocks from secondary kernels. TSK_NAMEPAR must be defined for this option to work. Since it may be desirable to switch off the handling of the names after the debugging phase, without having to change all create_xxx calls to omit the name parameter, the name parameter is ignored if TSK_NAMED is undefined, but TSK_NAMEPAR is defined. This option is normally enabled (TRUE). It must be enabled for DOS. GROUPS If enabled, task groups, i.e. multiple invocations of CTask, are supported. This option is normally enabled (TRUE). It must be enabled for DOS. CLOCK_MSEC If TRUE, all timeouts are specified in milliseconds instead of timer ticks. This allows programming of delays and timeouts independent of the speedup-parameter or the system tick rate. This option is normally disabled (FALSE). PRI_TIMER Specifies the priority of the timer task. Normally the timer task should have a higher priority than any other task in the system. The value is normally 0xf000. PRI_STD This value may be used in your programs as the standard priority of user tasks. Its value is arbitrary. It is not used in the kernel except for the definition of PRI_INT9 (see below). The value is normally 100 (decimal). Ctask Manual - Version 2.2 - 90-10-12 - Page 18 PRI_INT8 Determines the priority of the "int8"-task. This task chains to the previous interrupt vector for the sytem timer tick, and thus may activate resident TSR's. Since TSR's normally use polling when accessing the keyboard and other devices, the priority of the int8-task should be equal to or lower than normal user-defined tasks to allow your program to con- tinue to run while the TSR is active. You can tune this value so that some tasks are blocked by the TSR to avoid trashing the screen. The value is normally PRI_STD. AT_BIOS If enabled, the AT BIOS wait/post handler is installed. May be disabled when compatibility problems arise. You can also disable installation of this handler with an install flag in the install_tasker call, but using the configuration flag will save some code. Embedded systems likely will use FALSE. This option is normally enabled (TRUE). INT8_EARLY If TRUE, the timer interrupt always uses early INT8 proces- sing, regardless of the IFL_INT8_EARLY installation flag. Setting this flag saves some code and data, but eliminates some flexibility. Under DOS, timer ticks can be missed under certain circumstances when set, so DOS based configurations always should use FALSE. The installation flag has a slightly different effect, and may be used under DOS with no adverse effects. Embedded systems likely will always use TRUE. This option is normally disabled (FALSE). INT8_LATE If TRUE, the timer interrupt always uses late INT8 proces- sing, regardless of the IFL_INT8_EARLY installation flag. Setting this flag saves some code, but eliminates some flexibility. Embedded systems likely will always use FALSE. This option is normally disabled (FALSE). IBM DOS Both IBM and DOS are more or less of informative value only, to point out those areas in the kernel that need attention when converting to non-IBM or non-DOS environments. Disabling one or both of this options requires the substitution of your own routines for installation, timer, and keyboard handling. Both options must normally be enabled (TRUE). Ctask Manual - Version 2.2 - 90-10-12 - Page 19 SINGLE_DATA If enabled, only a single global data block is used. This speeds up processing, but prohibits linkage of multiple groups. Useful for dedicated systems, and also if your program is known to never interact with another copy of CTask. Should be left FALSE if you're not so sure, must be FALSE if GROUPS is enabled. The current version of the DOS handler requires GROUPS to be used, so it should only be TRUE for embedded systems. This option is normally disabled (FALSE). EMS If TRUE, EMS support is included. For DOS applications using spawn or going TSR, this should always be TRUE, unless it is known that the program will never be executed in an EMS environment. It must also be TRUE for programs using EMS. This option is normally enabled (TRUE). EMS_SAVE_SIZE Size of the EMS page info save area. For LIM 4.0 drivers, only four pages are saved, so 16 bytes should be sufficient. If the partial page map function is not available in the driver, more space may be required for holding the full page map. The value is normally 16. NDP If TRUE, 80x87 support is included. If this option is enabled, and no coprocessor is present, the machine can hang if the BIOS equipment configuration is set incorrectly. NOTE: Coprocessor support is not yet tested. Please report your experiences with this option. This option is normally disabled (FALSE). HOTKEYS If TRUE, keyboard hotkey support is included. Embedded systems likely will not use hotkeys, and may set this to FALSE. This option is normally enabled (TRUE). CHECKING Enables pointer and stack checks when TRUE. Checking pointers and task stacks slows down the system, but it is highly recommended to enable this option during development. Only turn off checking after debugging is complete. This option is normally disabled (FALSE). Ctask Manual - Version 2.2 - 90-10-12 - Page 20 Memory Allocation TSKALLOC.C is needed if TSK_DYNAMIC is enabled in tskconf.h to handle the allocation and free calls. If you want to use dynamic allocation in your own tasks, you should also use the functions tsk_alloc and tsk_free to avoid the reentrancy problems mentioned in the introduction. If you should need other forms of alloc (like calloc) the recommended way is to add those functions to TSKALLOC.C, requesting the resource alloc_resource before calling the C memory-allocation function. Joe Urso provided the following tip on how to force all memory allocation to pass through the resource handling functions: "I have found that some MS Library functions call the allocate and free library functions, namely the first call to fread(), fopen(), and fclose(). To fix this situation I have - extracted FMALLOC from the llibce library, - renamed the functions within that object (via the Norton Utilities) to the upper case spelling of the functions (FREE, MALLOC, _FFREE and _FMALLOC) and replaced the file in the lib. I also did the same for object EXPAND because of the function REALLOC. - then modified TSKALLOC.C to contain the lower case spelling of malloc, free, and expand. These functions aquire the alloc resource, then call the upper case spelling of the name. At link time I now link with /NOIGNORECASE and /NODEFAULTLIB." An option is provided in tskalloc.c to compile the module with the modifications suggested by Joe Urso. Snapshot TSKSNAP.C is only needed if you want to include the snapshot dump into your program. Note that you can *not* use snapshot if you disable TSK_NAMED in tskconf.h. Ctask Manual - Version 2.2 - 90-10-12 - Page 21 Task Stacks When compiling your application, turn stack checking off. The standard stack check is of little use with task stacks, and may interfere with CTask's operation. The stack area for tasks should be allocated on the main program's stack, not in the static or heap data space. The reason for this is that some of the C library routines check for stack overflow regardless of your compile-time switches, and will crash your application if you use stacks outside the normal stack. The stack allocation parameter with LINK (MS-C), or the _stacksize variable (Turbo C) have to be increased to reflect the additional stack space. When calculating task stack sizes, keep in mind that library routines (esp. printf) allocate a lot of space on the stack for temporary variables. A minimum of 1k for tasks using library routines is recommended, 2k puts you on the safe side. Tasks not using C library routines may use a smaller stack, about 256 bytes at a minimum, plus space for any local variables and nested routines. Then add up all task stacks, and add space for the main task (the function calling install_tasker), with this size also dependent on what you will do in the main task while CTask is active. Stacks for tasks that do not use C library routines may be allocated anywhere. If you have the CHECKING option enabled, the snapshot dump will output the number of unused bytes of stack for each task. This can help you determine the optimum stack size for your application. Drivers The keyboard and DOS handlers are always installed with CTask. Using the serial I/O and printer drivers is optional, so you have to install them separately, but only *after* installing CTask. When using the serial driver, include "sio.h" in your modules, when using the printer driver, include "prt.h". Another driver that is automatically installed is the BIOS wait/post handler for the IBM AT. The AT BIOS contains some multitasking hooks to avoid busy waiting in the BIOS. If you experience problems with disk accesses or printer output through BIOS (not through the CTask printer driver), you should disable installation of this driver by setting AT_BIOS to zero in tskconf.h, or not specifying the IFL_INT15 flag in install_tasker. Normally, no problems should arise with this driver even in XT type machines. Ctask Manual - Version 2.2 - 90-10-12 - Page 22 Things to remember Remember that tasks are not automatically started after creation. Use start_task to allow a created task to run. Always use create_xxx on resources, pipes, etc. Using the event routines without doing so will have unpredictable results. This is especially true with the new queue structure introduced in 2.0/2.2, where uninitialised control structures will invariably lead to a system crash. Enable the CHECKING option to trap such cases. Before exiting the program, all installed drivers and CTask should be explicitly removed. Although the DOS handler traps the terminate call and automatically calls remove_tasker, you should make sure that all tasks are completed properly, and call remove_tasker yourself. Deleting events before exiting the program is not mandatory, but recommended to kill all tasks waiting for the event. You should be careful not to kill tasks while they are active in DOS. The kill_task routine should be reserved for fatal error handling. The best way is to let the tasks kill themselves depending on some global variable or event. If a task is killed while waiting for input in DOS, DOS operation may be severely impaired. If you use the C console input routines, make sure that the task returns from DOS before it is killed, if necessary by requesting the user to press a key. Priority Handling CTask provides for prioritized task execution and event processing. This means that a task that has a higher priority will be run before any other tasks having lower priority. Also, a higher priority task will gain access to resources, counters, pipes, and mail, before lower priority tasks. With fixed priorities, this means that a high priority task can monopolize CPU time, even if it calls schedule() explicitly. Variable priority increases each eligible task's priority by one on each scheduler call, so that lower priority tasks will slowly rise to the head of the queue until they get executed. The priority will be reset to the initial priority when a task is run. Since variable priority increases processing time in the critical region of the scheduler, it is not recommended for systems in which a larger number of tasks is expected to be eligible simultaneously. Usually, all tasks in a system should have the same priority, with only very few exceptions for non-critical background processing (low priority) or very time-critical tasks (high Ctask Manual - Version 2.2 - 90-10-12 - Page 23 priority). High priority tasks should be written in such a way that they either reduce their priority when processing is completed, or that they wait for an event. Busy waiting in a high priority task will severely impair system operation with variable priority enabled, and will stop the system until the task is placed in a waiting state with fixed priority. The (automatically created) main task is started with the highest possible priority below the timer task, so that it can process all initialisations before other tasks start running. To allow the system to operate, the priority of the main task must be reduced, or the main task must wait for an event or a timeout. Ctask Manual - Version 2.2 - 90-10-12 - Page 24 Multitasking and DOS CTask includes (and automatically installs) a routine which traps all DOS calls, and makes sure that no two tasks simultaneously enter DOS. This is accomplished using the resource mechanism, with special provisions for the limited multitasking capabilities provided by DOS. There are a few calls, namely those with function codes <= 0x0c, which allow functions with codes > 0x0c to be executed while DOS is waiting for an external device (generally the keyboard) to get ready. This, however, limits the use of some C library functions, namely scanf and fread, for console input. Both these functions use handle input, and thus can not be interrupted. When writing routines for handling user input, keyboard read functions should either use the low-level calls getch and gets, or, better yet, the direct entries into the keyboard handler, t_read_key and t_keyhit, and then process the string with sscanf if desired. The keyboard handler (contained in tskkbd.asm) traps all keyboard interrupts, setting a flag when a key is hit. If a task reads from the keyboard, it is automatically made waiting if there is no key to read. Using getch and gets is less desirable since they use polling instead of event waiting, and thus degrade system performance. Also, the t_read_key and t_keyhit functions do not use DOS, so DOS functions <= 0C can be executed concurrently. The BIOS interrupts 10 (Video), 13 (Disk), and 16 (Keyboard) are protected by CTask. Using other BIOS interrupts directly should generally be avoided, unless you are absolutely sure they will not be used by other routines via DOS, or you provide your own critical region handling. Protection of INT 10 is optional, and should only be used if you expect to use BIOS level video output in parallel to other tasks. Since INT 10 calls occur extremely frequent in most programs, the overhead for reserving and releasing the resource can slow down the system noticeably. Starting with version 1.2, the DOS handling has been extended to automatically save and restore the DOS variable context on a task switch. This is done by directly saving the critical variables of the DOS data area in the task control block. An undocumented DOS call is used to determine location and length of this area. NOTE that this call is not available in DOS versions prior to 3.1, and may not be available in MS-DOS clones or emulators. This context save allows multiple DOS applications to run concurrently. The DOS access module has been tested to work with PC-DOS and MS- DOS versions 3.20, 3.30, 4.00, and 4.01. There were also no problems with the DOS PRINT program, and with Network drivers (Invisible Net) running in the background. Special provisions are built into the DOS module to detect background DOS calls. Using Sidekick also hasn't lead to any problems, although you may trash Ctask Manual - Version 2.2 - 90-10-12 - Page 25 Sidekick's screen display by writing to the screen while Sidekick is active (note that your application *continues* to run while Sidekick or other pop-ups are active). I can not guarantee complete compatibility with all background and pop-up programs under all versions of DOS. Specifically, DOS versions prior to 3.1 have significant problems with multitasking, and do not support the variable save call necessary for full DOS multitasking. Upgrading to a newer DOS version is recommended if you are still using DOS < 3.2 (DOS 3.1 has some bugs in other areas). Also starting with version 1.2, CTask is now compatible with MS- Windows in non-enhanced mode. It has been tested to work with Windows 286 1.2 and 2.1, and with Windows 3.0 in real mode, but the mechanism used should work with other non-preemptive versions, too. CTask can be installed as a background TSR before starting Windows, or you may spawn Windows from CTask. Windows/386 is a special virtual-mode operating system and can generally not be combined with other multitaskers. CTask 2.2 will not work with Windows 3.0 in 386 enhanced mode when installed as a TSR before starting Windows. I now know why, but I did not have the time to do anything about it. The next version probably will support full Windows 3.0 compatibility. If you start CTask within Windows, everything will work smoothly, but CTask instances in different DOS-windows will not be able to communicate with each other. Other preemptive multitaskers like DesqView will most likely not coexist peacefully with CTask. Critical errors and Control C occurring while concurrent DOS access takes place may be fatal. Using the ctrlbrk() and harderr() functions of Turbo C, or their equivalents in MS C, to trap critical errors and Control C is highly recommended. Error handlers should be installed before CTask is installed. Spawning and CTask TSR's Starting with Version 1.2, CTask programs can now spawn other programs, and Terminate and Stay Resident (TSR). The DOS context switch, plus the saving and restoring of interrupts 21-24, on every task switch, makes it possible to have multiple, nearly completely independent, programs running under DOS. But please note that CTask is not intended as a replacement for true DOS- multitaskers like DesqView. Implementation of such a system would surely be possible, using CTask as a base, but would require keeping track of all DOS control blocks. This is left as an exercise to the reader. The new features are intended to allow you to easily write background data aquisition or communication modules that run in parallel to other DOS applications. Ctask Manual - Version 2.2 - 90-10-12 - Page 26 Since the spawned program might itself be a CTask program, Version 1.2 automatically checks for the presence of a background copy of CTask. If one is found, the secondary invocation will link to the global data of the first CTask copy, making it possible to easily communicate between independent instances of CTask programs. The naming mechanism has been slightly changed to make it easier to find a task or data structure by name. For example, you could write a communications program in two separate parts. One part, the resident part, contains interrupt handlers and the protocol routines. The other part, the transient portion, contains the driving program, with editor, menus, script language and so on. If the resident part is started, it first spawns the transient part, which handles setup, and starts communications. Both parts can communicate using all CTask mechanisms, i.e. pipes, buffers, mailboxes etc., with the transient part obtaining the pointers to the CTask structures defined in the resident part via the structure name. Now if an up- or download is started, the transient part can exit to DOS, and the resident part can spawn a copy of command.com. Voila - background up/download with minimum hassle. Task Groups Each invocation of the CTask kernel (i.e. each call of the install_tasker routine) creates a new "Task Group". This group chains all tasks and other control structures created by this program together, so they can be killed if the group terminates (through a DOS call or the remove_tasker routine). Although it is recommended to kill all structures before terminating, there are a number of situations where this is hard to control under DOS. So CTask tries to take a few safety measures to make sure the system does not crash due to pointers chaining into nowhere. But please note that care should be taken not to "pull the rug under a group's feet". CTask will attempt to clean up memory when a group terminates. However, if that group has spawned another non-CTask program, CTask doesn't know about it, so an orphan will be left in memory, and you might even manage to get the system into an unstable state. And, there are a few restrictions. Although it is possible to create multiple groups running, and terminating, independently in parallel, those groups must be created by separate tasks from one "home group". If one task creates a group, and the same task, or another task from this group, creates a second, then it is not possible to terminate the first group without also killing the second. You can view this like a tree, where you can cut off branches, but all sub-branches of that branch will come down with it. The root of that tree, the primary invocation of CTask, can not be killed without killing the whole tree. Ctask Manual - Version 2.2 - 90-10-12 - Page 27 Also, it is mandatory that you at least try to call remove_tasker on termination. CTask can trap a program's termination, but this happens at a time when all the program's memory has already been released by DOS. This can lead to extremely dangerous situations if other tasks, or TSR's, allocate and modify this memory before CTask finishes it's cleanup. CTask will stop preemption while it is removing the group, but it still is definitely not recommended to rely on this mechanism. A sample for a task group structure follows: -Root- home level branch -----+ ^ ^ | | | | | | v -Group1- | | -Group2- home ------+ +----- home level <------------- level branch -----+ branch ^ ^ | | | | | | v -GroupA- | | -GroupB- home -----+ +----- home level <------------ level branch branch In this sample, Groups 1 and 2 were created by different tasks in the Root group, Groups A and B by different tasks in Group 1. Three pointers are used in chaining groups. The 'branch' points to the first element in an unordered list of task groups on the same "branch level" one level "up" the tree. Those groups are chained by the 'level' pointer. To allow finding the home group when going "down" the tree (towards the root), all groups on the same level point there through the 'home' pointer. In this sample, you could kill Group2 without affecting Group1 or it's subgroups. Killing Group1 will terminate GroupA and GroupB. Ctask Manual - Version 2.2 - 90-10-12 - Page 28 How does CTask work Queues CTask uses priority queues for most of its functions. A priority queue differs from the usual FIFO (first in, first out) queues in the insertion of elements into the queue. Rather than just placing new elements after the last queue member, the priority of the task determines its place in the queue. A task is enqueued after all queue members with higher or equal priority, but before any member with lower priority. Removal from the queue takes place at the first element. These queues are used with all operations in which a task is made waiting, be it waiting to get run, or waiting for an event. The advantage of this is the simplicity of implementing priorities. Other schemes might rely on arrays of queues, or searching through lists, to determine the highest priority waiting task. With priority queues, the most time critical function, scheduling, is very fast, since it can simply take the first task from the queue of eligible functions. The disadvantage is the time required to step through all greater or equal priority members of a queue to find the right place to insert the task. But since the number of tasks simultaneously enqueued in the same queue is normally relatively small with most multitasking systems, this disadvantage is more than offset by the simple, and thus easy to implement efficiently, scheme. Version 2.0 generalizes the queueing scheme, and uses doubly linked lists for all internal chains (except the ticker chain). The introduction of the "yield" function, which inserts a task at the end of the eligible queue, but resets the priority, mandated searching through the queue from the back end. The previous scheme, which walked the queue from the front end, could lead to task starvation in a system with polling tasks when yielding. Also, the timer algorithm was changed such that the timer task didn't have to step through all timeout elements, but rather to only decrement the first queue element ticker. This is implemented by storing the timeout as a tick difference to the next queue element rather than as an absolute value. Doubly linked lists make insertion and removal of elements at arbitrary points very simple, and eliminate the time needed to find an element in a queue. To alleviate the additional overhead associated with managing dual pointers, the main queueing routines were coded in assembler. Especially when operating with multiple far pointers, the code generated by the C compilers even with maximum optimization is not that impressive. The corresponding C code is included as a reference, and to aid porting to non-8086 environments. Ctask Manual - Version 2.2 - 90-10-12 - Page 29 The Scheduler In a CTask system, there is at least one essential queue: the eligible queue, which contains all tasks waiting to run. Each time the scheduler is invoked, it will first save all processor registers in the current task control block, and then enqueue the current task into the appropriate queue. Normally, this will be the eligible queue. Then the first element in the eligible queue is removed from the queue, the stack is switched to the stack of this task, and processor registers are restored from the new TCB, returning to the point where the new task was interrupted. If the eligible queue is empty the scheduler will loop with interrupts enabled. The queue head pointer of the task control block of the current running task determines what will happen to the task when the scheduler is invoked. If it points to an event control block, the task will be enqueued as waiting for this event. If it is NULL, the task will not be enqueued in any queue, effectively stopping it. If it points to the eligible queue, the task will be enqueued there. In any case, the scheduler does not care what queue the task is to be enqueued in, since all queues use the same priority based ordering. If a task is no longer in the eligible queue, it can only be returned to this queue by an external event. Events External events can take several forms, which are relatively similar on the inside. All CTask events use a control block, with at least one queue for tasks waiting for the event. Although it would have been possible to summarize all events under a global structure, this approach was not used in CTask, the main reasons being execution speed and ease of use. So if you scan through the source files for CTask events, you will see many very similar routines, which only differ in the types of data and the names of queues they process. In a class based language like C++, one would certainly define all events as instances or derivations of one class. In plain C, the necessary type casting, and the different handling of certain cases, would clobber the code to the point of illegibility. Resources The event types "resource", "flag", and "counter" differ only in the kind of wait operations and the handling of the state variable. The resource is mainly for use in interlocking critical regions of code, to protect access to non-reentrant resources. Only one task can "own" a resource, all other tasks requesting the resource are delayed until the owning task releases it. For added protection, CTask stores the task control block address of the current owner of the resource in the resource control block, so no other task can erroneously release it. Ctask Manual - Version 2.2 - 90-10-12 - Page 30 Flags Flags, on the other hand, can be set and cleared by any task, and also by interrupt handlers. Tasks can wait on either state of the flag, and all tasks waiting for a state are simultaneously activated when the flag is changed to this state. This makes flags suitable for use as a global signalling mechanism. Counters Counters are a variation on the flag concept. A counter can be incremented and cleared by any task, and by interrupt handlers. Tasks can wait for a counter to be zero or nonzero. Like flags, all tasks waiting for the zero state are activated simultaneously. But unlike flags, only the first task waiting for the nonzero state of a counter will be activated on incrementing the counter, and the counter will be automatically decremented by one. The counter is used inside CTask to handle timer interrupts. The timer counter will be incremented on each timer tick, activating the timer task. If for any reason the timer task is unable to complete its run until the next tick, this tick will not be lost, since the counter is incremented, and the timer task will continue to run the next time it calls the counter wait request. Mailboxes and Pipes The "mailbox" and "pipe" events can be used for inter-task communication, and for the communication between interrupt handlers and tasks. Mailboxes can hold an unlimited number of mail blocks. Mail blocks have no fixed structure, but the first doubleword in each block passed to a mailbox routine is used as a chain pointer. Mail blocks are chained into a mailbox in FIFO order. Tasks can wait for mail to arrive, or can conditionally read mail if a block is available. Tasks and interrupt handlers can write blocks to a mailbox. Since mailboxes don't need any copying of data, they are suited for high speed exchange of larger amounts of data between tasks. The disadvantage of sending mail this way is that you have to make sure that a mail block is not re-used before it has been read out of the box and processed by the receiving task. When exchanging fixed length messages, you can build a free mail block chain by using a mailbox to hold the available blocks. Buffered message exchange is possible using pipes. When creating a pipe, you specify a buffer area and its length, and the pipe routines will buffer all data written to the pipe in this area. This implies that writing to a pipe may cause a task to be delayed until there is space available in the pipe. To allow interrupt handlers to write to pipes, there is a conditional Ctask Manual - Version 2.2 - 90-10-12 - Page 31 write request, which will simply return if the pipe is full. Tasks can wait for data to arrive in a pipe, and for the pipe to be emptied. A conditional read request is also provided. The disadvantage of pipes is that they are slightly slower than mailboxes due to the necessary copying, and that you can only place word or byte sized items in a pipe. When there is more than one reader or writer task, you can not rely on the bytes in a pipe being in any specific order. A "buffer" construct is provided in CTask that expands pipes to allow arbitrary length messages to be written and read. This is implemented using a resource for reading and writing to the pipe associated with the buffer, so the message is always guaranteed to be written and read in one piece. But since resources can not be used in interrupt handlers, using such buffers is not allowed from interrupts. Serial and Printer Drivers There are a number of routines included in the CTask package for PC-specific tasks. Although they will be of limited use for embed-ded applications, studying the serial I/O and printer interface routines will give you some hints on how to use the CTask kernel for implementing your own device drivers. For PC based appli-cations, the routines should be usable with no or little changes for implementing complete communications packages. The serial I/O handler uses interrupts for both input and output of data, and supports both XON/XOFF and RTS/CTS handshake methods. The modem inputs can selectively be enabled to control data transmission. Pipes are used for transmit and receive data, with the buffer and its size specified on initialization. Both COM1 and COM2 can be active simultaneously, and other ports can be supported by editing a table in the source code or defining ports on-line. Since CTask allows the access to all events in interrupt handlers, writing interrupt based I/O drivers is relatively simple. On receiving a character, the character and any associated errors are placed in the receive pipe, and the transmit pipe is read on transmit ready interrupt. Note that conditional reads and writes have to be used in the interrupt handler, since you can't safely delay an interrupt handler. The printer output driver supports both polling and interrupt output. Again, a pipe is used for the output characters. However, since polling is supported, and because of the somewhat unreliable interrupt structure of the printer ports, a driver task is required. This task is automatically created on installing the driver. The task first waits on the pipe for a character to be written to the printer. When polling is enabled, it tries to output the character directly, using a short busy- waiting loop. So as not to load the system too heavily by the polling, the task will yield if it can't output the character after a small number of loops. When interrupts are enabled, the Ctask Manual - Version 2.2 - 90-10-12 - Page 32 process is essentially the same at the start, but after the character is written to the port, the task will wait on a flag to be set. The interrupt handler will set the flag on interrupt, enabling the task to get the next character from the pipe. Since interrupts are unreliable with most printers due to the usually very short pulses on the acknowledge line, the task uses a timeout on the flag wait, so it does not hang if an interrupt is missed. Studying the printer driver will also give you an idea what the optional parameter on task creation can be used for. In the printer driver, this parameter is used to pass the address of the printer control block, which contains the pipe, the flag, and the hardware info, to the task. This allows the printer driver to be simultaneously installed for any number of printers without having to write separate printer tasks. Ctask Manual - Version 2.2 - 90-10-12 - Page 33 CTask Data Types Note that you do not have to know the innards of the structures. All structure fields are filled by the "create_xxx" routines and modified by the CTask functions. You should NEVER modify a field in one of the structures directly. The structures are explained here shortly only for those wanting to modify the routines. NOTE: When modifying CTask structures, take care to modify the equivalent definitions in the assembler include file "tsk.mac". Some of the assembler routines have to use field offsets into pointers, so having different offsets in C and assembler will crash the system. If you only want to use the routines, you should simply include the file "tsk.h" in your source, and define variables of the types tcb - for task control blocks tcbptr - for far pointers to tcbs flag - for flag events flagptr - for far pointers to flags resource - for resource events resourceptr - for far pointers to resources counter - for counter events counterptr - for far pointers to counters mailbox - for mailbox events mailboxptr - for far pointers to mailboxes pipe - for pipe events pipeptr - for far pointers to pipes wpipe - for word pipe events wpipeptr - for far pointers to word pipes buffer - for buffer events bufferptr - for far pointers to buffers tlink - for timeout and watch control blocks tlinkptr - for far pointers to timeout control blocks namerec - for control block names nameptr - for name pointers without caring what's behind them. Ctask Manual - Version 2.2 - 90-10-12 - Page 34 Additionally, you may use the types byte - for unsigned characters word - for unsigned short integers dword - for unsigned long integers funcptr - for far pointers to void functions funcptr_void - for far pointers to void functions taking no parameters funcptr_int - for far pointers to void functions taking a single int parameter funcptr_fp - for far pointers to void functions taking a single far pointer parameter funcptr_dword - for far pointers to void functions taking a single doubleword parameter farptr - for far pointers to anything byteptr - for far pointers to byte arrays wordptr - for far pointers to word arrays in defining or typecasting items to be passed as parameters to CTask functions. Other definitions The following definitions are used inside CTask to avoid problems with Microsoft C in some memory models. The standard FP_SEG and FP_OFF macros will not work correctly in near data models, and the NULL pointer may not actually be 0 when assigned to a far pointer. The offsetof operator is not defined for MSC 5.1. TFP_SEG(ptr) Is a macro to isolate the segment part of a far pointer. TFP_OFF(ptr) Is a macro to isolate the offset part of a far pointer. TMK_FP(seg,off) Is a macro to make a far pointer out of a segment and an offset. LNULL Is a far pointer to nothing. TSK_OFFSETOFF(struc,field) Is a macro that returns the byte offset of "field" within the structure type "struc". TSK_STRUCTOP(struc,ptr,field) Is a macro that returns a pointer to the start of the structure of type "struc", given a pointer "ptr" which points to "field" within the structure. Ctask Manual - Version 2.2 - 90-10-12 - Page 35 The definition TN is used in CTask starting at version 2.1 to avoid using extensive #if directives for routines accepting name parameters. The previous way of enclosing the parameter in #if / #endif made the sources hard to read. The TN macro will expand to nothing if TSK_NAMEPAR is FALSE, and to a comma followed by the parameter if TSK_NAMEPAR is TRUE. TN(name) Define name parameter if TSK_NAMEPAR is TRUE. In addition, a number of definitions are provided to statically initialise event structures (flags, resources, etc.). Those definitions (DEF_xxx) are listed in the "routines" section under the corresponding create_xxx routine entry. You use them in place of a normal variable definition, i.e. to create an initialised flag, you would write static DEF_FLAG (myflag, "MyFlag"); ... add_event_name (&myflag); instead of static flag myflag; ... create_flag (&myflag, "MyFlag"); Typedefs used for simplified type specifications typedef unsigned char byte; typedef unsigned short word; typedef unsigned long dword; typedef void (Taskfunc *funcptr)(); typedef void (Taskfunc *funcptr_void)(void); typedef void (Taskfunc *funcptr_int)(int); typedef void (Taskfunc *funcptr_dword)(dword); typedef void (interrupt far *intprocptr)(void); typedef void far *farptr; typedef byte far *byteptr; typedef word far *wordptr; Ctask Manual - Version 2.2 - 90-10-12 - Page 36 Error return values for event wait functions #define TTIMEOUT ((farptr) -1L) #define TIMEOUT (-1) -1 is returned if a timeout occurred while waiting for an event. #define TWAKE ((farptr) -2L) #define WAKE (-2) -2 is returned if the task was waked up while waiting for an event. #define TWATCH ((farptr) -3L) #define WATCH (-3) -3 is returned if the task was waked up during a wait by a watchpoint or hotkey action. Queues The 'queue' structure is a dual link for linking task control blocks and timer blocks. The first three fields are used both for the queue head, and for elements to be inserted in a queue. CAUTION: Do not change the order of the first three fields in either queue or queue_head! Those two structures are used interchangeably in various places in the CTask kernel. Changing one of them would have catastrophic results. The queue element ("queue") contains the forward and backward pointer, a structure kind field, plus the priority (when used in a TCB) or the timeout value (when used in a tlink structure). The kind field is used to identify the type of structure the queue element is a part of, and also to identify the "end" of the queue. To simplify insertion and removal, all queues are circular in nature, i.e. there is no NULL-pointer at the head or tail. The queue head, and thus the end of a queue, is identified by a bit 7 (Q_HEAD) being set in the kind field. #define Q_HEAD 0x80 /* Queue head flag */ typedef struct { word prior; word ini_prior; } qelem_pri; typedef struct queue_rec far *queptr; Ctask Manual - Version 2.2 - 90-10-12 - Page 37 typedef struct queue_rec { queptr volatile next; queptr volatile prev; byte kind; union { qelem_pri pri; dword ticks; } el; } queue; The queue head ("queue_head") also contains the forward and backward pointer, and the structure kind field. The same structure is also used to chain name and timeout/watch/hotkey blocks, since those do not need the priority/tick field present in normal queue elements. typedef struct { queptr volatile first; queptr volatile last; byte kind; } queue_head; typedef queue_head far *queheadptr; The timer/watch/hotkey control block The timer control block is included in every task control block. It may also be created as a separate entity to specify special actions to be executed after or every n timer ticks, to specify memory or port locations to be watched for a change or a certain value on every timer tick, or for keyboard hotkeys. The "link" field links the active structures into the timer, watch, or hotkey queue. The kind of the element (which is specified by the "kind" field of "link") determines the appropriate queue. The "chain" field (present only if task groups are enabled) links all timer structures of a group. This allows automatic removal of elements on termination. The "next" field is exclusively used by the timer task to chain elements that have to be activated. Ctask Manual - Version 2.2 - 90-10-12 - Page 38 "strucp" points to the structure to be acted upon, "struckind" specifies the kind of structure: #define TKIND_TASK 1 Strucp points to the task control block of which the element is a member. The task will be awakened when the timeout expires. #define TKIND_WAKE 2 Strucp points to a task control block. Otherwise same as TKIND_TASK. #define TKIND_PROC 3 Strucp contains the address of a function to be called on timeout. #define TKIND_FLAG 4 Strucp points to a flag that should be set on timeout. #define TKIND_COUNTER 5 Strucp points to a counter that should be increased on timeout. #define TKIND_COUNTDEC 6 Strucp points to a counter that should be decreased on timeout. The timeout structure is used for timeouts, memory/port watchpoints, and hotkeys. The union "elem" contains either the tick reload value, the specs for the memory or port location to watch, or the hotkey scancode and flag values. "elkind" specifies the kind of structure used in the upper nibble: #define TELEM_TIMER 0x10 This is a timeout element. #define TELEM_MEM 0x20 This is a memory watch element. #define TELEM_PORT 0x30 This is a port watch element. Ctask Manual - Version 2.2 - 90-10-12 - Page 39 #define TELEM_HOTKEY 0x40 This is a keyboard hotkey element. The lower nibble of "elkind" is used for watchpoints, it specifies the comparison operation: #define TCMP_EQ 1 Activate watch if value read is equal to "compare". #define TCMP_NE 2 Activate watch if value read is not equal to "compare". #define TCMP_GE 3 Activate watch if value read is >= "compare" (unsigned). #define TCMP_LE 4 Activate watch if value read is <= "compare" (unsigned). #define TCMP_GES 5 Activate watch if value read is >= "compare" (signed). #define TCMP_LES 6 Activate watch if value read is <= "compare" (signed). #define TCMP_CHG 7 Activate watch if value read is not equal to "compare". Additionally, store the value read into the "compare" field. Only useful for continuous watchpoints. For timeouts, "elem.time" contains the "reload" value used for repetitive timeout actions to reload the original timeout value. The actual timeout value is part of the link structure. For port watches, "elem.port" contains the values "port", "mask", "compare" and "in_word". "port" holds the port number to read from. The value read is masked with "mask", and compared with "compare". A word access is used if "in_word" is nonzero. Memory watches are similar to port watches, with "elem.mem" containing "address", the memory address to watch, and "mask" and "compare" as above. Ctask Manual - Version 2.2 - 90-10-12 - Page 40 Keyboard hotkeys hold the three BIOS keyboard flag comparison values, and the keyboard scancode, in "elem.key". The "flags" field holds both permanent and temporary processing flags: #define TFLAG_BUSY 0x01 If this bit is set, the timer task is busy processing this element. It may not be deleted or de/enqueued. Routines processing timer elements must not modify the control block except the flag field. #define TFLAG_ENQUEUE 0x02 The element is to be (re-)enqueued in the appropriate queue after processing. This is a temporary flag, used only while TFLAG_BUSY is set. #define TFLAG_UNQUEUE 0x04 The element is to be removed from its queue after processing. This is a temporary flag, used only while TFLAG_BUSY is set. #define TFLAG_REMOVE 0x08 The element is to be deallocated after processing. This is a temporary flag, used only while TFLAG_BUSY is set, for elements with TFLAG_TEMP set. #define TFLAG_REPEAT 0x40 The element is a repeat element. For timeout elements, the timeout count is reloaded on activation. Other elements are re-enqueued without change when activated. #define TFLAG_TEMP 0x80 If this bit is set, this is a temporary element, which will be deallocated on activation or delete. The "user_parm" field may be used to pass pointers or other values to timeout functions. It is not modified by the CTask kernel routines. Ctask Manual - Version 2.2 - 90-10-12 - Page 41 typedef struct tlink_rec far *tlinkptr; struct telem_memwatch { wordptr address; word mask; word compare; }; struct telem_portwatch { word port; word mask; word compare; byte in_word; }; struct telem_timeout { dword reload; }; typedef struct { byte mask; byte compare; } kbflag; struct telem_hotkey { kbflag flag1; kbflag flag2; kbflag flag3; byte scancode; }; struct tlink_rec { queue link; tlinkptr next; farptr strucp; dword user_parm; queue_head chain; (if GROUPS) union { struct telem_memwatch mem; struct telem_portwatch port; struct telem_timeout time; struct telem_hotkey key; } elem; byte elkind; byte struckind; byte flags; }; typedef struct tlink_rec tlink; Ctask Manual - Version 2.2 - 90-10-12 - Page 42 The name link structure If TSK_NAMED is enabled, all structures except the timer control block contain a name link. All control blocks are linked and named via this element. "strucp" points to the head of the structure the name link is an element of, with "kind" in the list field specifying the type of structure: #define TYP_GROUP 0 Group control block #define TYP_TCB 1 task control block #define TYP_FLAG 2 flag event #define TYP_RESOURCE 3 resource event #define TYP_COUNTER 4 counter event #define TYP_MAILBOX 5 mailbox event #define TYP_PIPE 6 byte pipe #define TYP_WPIPE 7 word pipe #define TYP_BUFFER 8 buffer #define TYP_TIMER 9 timeout element #define TYP_WATCH 10 memory/port watch element #define TYP_HOTKEY 11 hotkey element The head element of the name list (normally the group control block) has the Q_HEAD bit in its kind field set. The "name" field contains an up to 8-character name plus a zero terminator. #define NAMELENGTH 9 typedef struct name_rec far *nameptr; struct name_rec { queue_head list; farptr strucp; char name [NAMELENGTH]; }; typedef struct name_rec namerec; The task control block structure The "cqueue" field links the TCB into one of the queues. The "qhead" pointer points to the head of the queue the task is enqueued in, or will be enqueued in on the next schedule request in the case of the current running task. The "prior" field in the cqueue structure contains the tasks current priority, with 0xffff the highest possible priority, and 0 the lowest. The "ini_prior" field initially contains the same Ctask Manual - Version 2.2 - 90-10-12 - Page 43 value. If variable priority is enabled, "prior" is incremented on each scheduler call, and reset to "ini_prior" when the task is activated. "stack" contains the saved task stack pointer (offset and segment) if the task is not running. The field "stkbot" contains the bottom address of the task stack. It is set by create_task, and is used by the scheduler and the snapshot dump module if checking is enabled to check for stack overflow and stack usage. The "t_ax", "t_cx", ..., "t_ds" fields hold the register contents while a task is inactive. "state" and "flags" contain the tasks state and flags. "timerq" is a tlink structure used to chain the tcb into the timer queue if the task is waiting for a timeout, into the watch queue if the task is waiting for a watch event, or into one of the hotkey queues if the task is waiting for a hotkey. See above for a description of the tlink structure. The fields "retptr" and "retsize" are used in event handling. They are used when a task is waiting for an event by the task activating the event, and also by timeout and wake to indicate error returns. The use of these pointers eliminates the need to loop for an event, which requires slightly more code in the event handling routines, but reduces the need for task switching. The "save_func" and "rest_func" pointers can optionally point to task-switch save and restore functions. In special applications, it may be necessary to save and restore global variables or other items when a task is deactivated. The save function is called when a task is deactivated, the restore function when a task is activated. Both functions should be defined as void Taskfunc funcname (tcbptr tcb); The functions are called with a pointer to the current TCB, DS is set up to point to the TCB data segment. Interrupts are enabled. The stack is the scheduler's local stack, so the routine must not use excessive local stack space. Calling CTask-routines that might cause the scheduler to be activated must be avoided. See the "Advanced Topics" chapter for more information. The "user_ptr" field can hold any pointer or other value to be used by the save/restore functions or to point to task-related items. This field is not modified by the CTask routines. The "group" and "homegroup" pointers link a task with it's current task group, and with the base group that created the task if the task spawned a secondary invocation of CTask. Ctask Manual - Version 2.2 - 90-10-12 - Page 44 The DOS-related fields "indos", "new", "base_psp", "psp_sssp", and "swap_area" are used to save critical information on the state of DOS. They should never be tampered with. The same goes for "sched_ent_func" which holds a function pointer to an internal function of the DOS module when a task is active in DOS. The "name" namerec structure is present only if TSK_NAMED is enabled. It may be used in debugging (see tsksnap.c for an example), and in applications where the address of the structure can not be passed directly. The "ems_map" and "ndpsave" fields hold the EMS and numeric coprocessor state, and are only present if the respective options are enabled. typedef struct tcb_rec far *tcbptr; struct tcb_rec { queue cqueue; queheadptr qhead; byteptr stkbot; volatile byte state; byte flags; byteptr stack; word t_ax; word t_cx; word t_dx; word t_si; word t_di; word t_bp; word t_es; word t_ds; tlink timerq; volatile farptr retptr; volatile int retsize; funcptr save_func; funcptr rest_func; farptr user_ptr; gcbptr group; (if GROUPS) gcbptr homegroup; (if GROUPS) funcptr sched_ent_func; (if DOS) volatile byte indos; (if DOS) volatile byte new; (if DOS) word base_psp; (if DOS) dword psp_sssp; (if DOS) byte swap_area [DOSSWAPSIZE]; (if DOS) namerec name; (if TSK_NAMED) byte ems_map [EMS_SAVE_SIZE]; (if EMS) ndpsave_t ndpsave; (if NDP) }; Ctask Manual - Version 2.2 - 90-10-12 - Page 45 typedef struct tcb_rec tcb; Task states #define ST_KILLED 0 The task has been killed. Restarting the task is not possible. Queue pointers are invalid. #define ST_STOPPED 1 The task is not enqueued in any queue. To be included in scheduling, it has to be explicitly started. The queue head pointer is NULL. #define ST_DELAYED 2 The task is enqueued in the timer queue only. When the timer expires, it is placed in the eligible queue. The queue head pointer is NULL. #define ST_WAITING 3 The task is waiting for an event to happen. It can also be chained into the timer queue if a timeout was specified in the call. The queue head pointer points to the queue head in the event control block for the event the process is waiting on. #define ST_ELIGIBLE 4 The task is enqueued in the queue of processes eligible for running. It can not be chained in the timer queue. The queue head pointer points to the eligible queue. #define ST_RUNNING 5 The task is the current running process. Although it is not enqueued in any queue, the queue head pointer in its control block is valid and points to the queue the process will be enqueued in on the next schedule request. Ctask Manual - Version 2.2 - 90-10-12 - Page 46 Possible state transitions and their reasons: stopped -> eligible by start_task () delayed -> killed by kill_task () -> eligible by timer task, or wake_task () eligible -> killed by kill_task () -> running by scheduler running -> killed by kill_task (), or return -> stopped by delay (0) -> delayed by delay (n != 0) -> eligible by scheduler -> waiting by wait_xxx () waiting -> killed by kill_task (), or event deletion -> eligible by event happening, timeout, or wake_task() Task flags System flags: #define F_TEMP 0x80 This tcb was allocated automatically, and must be free'd on task kill. #define F_STTEMP 0x40 The tasks stack was allocated automatically, and must be free'd on task kill. #define F_PERM 0x20 This is a "permanent" system task, it may not be killed. Ctask Manual - Version 2.2 - 90-10-12 - Page 47 User changeable flags: #define F_CRIT 0x01 This task may not be preempted. It will run until it clears this flag, delays itself, calls the scheduler explicitly, or waits for an event. #define F_USES_NDP 0x02 This task uses the numeric coprocessor. The NDP state must be saved/restored on a task switch. Do not set this flag if no coprocessor is installed. The Group Control Block Each invocation of CTask owns a group control block, gcb. This structure holds all information relevant to this invocation only, and chains all data structures created in this group. The "home", "level", and "branch" fields interconnect the groups (see the chapter on groups for more information). The "creator" field identifies the creating task. The "exit_addr", "create_psp", "save_psp", and "save_sssp" fields hold the information necessary to allow spawning CTask applications. The "namelist" field contains the name of the group itself, and links all structures created within this group. "main_ptr" points to the "main" task of this group, i.e. the task designated by a NULL tcb pointer. "remove" holds the last element in a chain of remove functions. This function is called whenever the group is uninstalled. The "telem_list" and "ticker_list" are the heads for the timer element and ticker lists. Timers and tickers are chained into this list to allow automatic removal on group termination. The "palloc" and "pfree" functions hold pointers to the allocation functions tsk_alloc and tsk_free. The functions are accessed through group-relative pointers to allow code sharing between invocations. Ctask Manual - Version 2.2 - 90-10-12 - Page 48 struct group_rec { gcbptr home; gcbptr level; gcbptr branch; tcbptr creator; dword exit_addr; word create_psp; word save_psp; dword save_sssp; namerec namelist; tcbptr main_ptr; callchainptr remove; queue_head telem_list; queue_head ticker_list; #if (TSK_DYNAMIC) farptr (Globalfunc *palloc)(word); farptr (Globalfunc *pfree)(farptr); #endif }; The event control blocks All event control blocks have two optional fields: "name" is only present if TSK_NAMED is enabled. It is a namerec structure as explained above. "flags" is only present if TSK_DYNAMIC is enabled. It contains F_TEMP If this control block was allocated automatically, and must be free'd on delete. F_STTEMP If the buffer for this event was allocated auto- matically, and must be free'd on delete (pipes and buffers only). The Ticker structure The ticker is not an event structure in the true sense, since there are no operations that wait on a ticker. It is the only control structure linked by a single forward pointer. It contains this "next" pointer, a doubleword "ticks" count that is counted down towards zero on every hardware clock tick, and the optional "flags" field. It is permissible to access and modify the "ticks" field directly. If task groups are enabled, an additional "chain" field links all ticker structures of a group to allow automatic removal on group termination. Ctask Manual - Version 2.2 - 90-10-12 - Page 49 typedef struct ticker_rec far *tick_ptr; typedef struct ticker_rec { tick_ptr next; dword ticks; queue_head chain; (if GROUPS) byte flags; (if TSK_DYNAMIC) } ticker; The Flag event structure Contains two queues for processes waiting on a flag state (clear or set), plus the flag state (0 = clear, 1 = set). typedef struct { queue_head wait_set; queue_head wait_clear; int state; byte flags; (if TSK_DYNAMIC) namerec name; (if TSK_NAMED) } flag; typedef flag far *flagptr; The counter event structure Similar to a flag, but contains a doubleword state counter. typedef struct { queue_head wait_set; queue_head wait_clear; dword state; byte flags; (if TSK_DYNAMIC) namerec name; (if TSK_NAMED) } counter; typedef counter far *counterptr; Ctask Manual - Version 2.2 - 90-10-12 - Page 50 The resource event structure Contains a queue for the tasks waiting for access to the resource, a pointer to the current owner of the resource (to check for illegal "release_resource" and nested request calls), and the resource request counter (0 = free, <> 0 = in use). typedef struct { queue_head waiting; queue_head owner; word count; byte flags; (if TSK_DYNAMIC) namerec name; (if TSK_NAMED) } resource; typedef resource far *resourceptr; The mailbox event structure The msgptr type is only used internally to chain mail blocks into the mailbox. The mailbox type contains a queue of the tasks waiting for mail, and a first and last pointer for the chain of mail blocks. struct msg_header { struct msg_header far *next; }; typedef struct msg_header far *msgptr; typedef mailbox far *mailboxptr; typedef struct { queue_head waiting; msgptr mail_first; msgptr mail_last; byte flags; (if TSK_DYNAMIC) namerec name; (if TSK_NAMED) } mailbox; The pipe and word pipe event structure Contains queues of the tasks waiting to read or write to the pipe, indices for reading (outptr) and writing (inptr) into the buffer, the buffer size, the number of bytes or words currently in the pipe ("filled"), and the pointer to the buffer. A word pipe is handled exactly the same as a byte pipe, the only difference being the element size placed in the buffer. With normal pipes, characters are buffered, with word pipes, words. Ctask Manual - Version 2.2 - 90-10-12 - Page 51 typedef struct { queue_head wait_read; queue_head wait_write; queue_head wait_clear; word bufsize; word filled; word inptr; word outptr; byteptr contents; byte flags; (if TSK_DYNAMIC) namerec name; (if TSK_NAMED) } pipe; typedef pipe far *pipeptr; typedef struct { queue_head wait_read; queue_head wait_write; queue_head wait_clear; word bufsize; word filled; word inptr; word outptr; wordptr wcontents; byte flags; (if TSK_DYNAMIC) namerec name; (if TSK_NAMED) } wpipe; typedef wpipe far *wpipeptr; The buffer event structure Contains resources for read and write access, the word pipe used for buffering, and a message counter. typedef struct { resource buf_write; resource buf_read; wpipe pip; word msgcnt; byte flags; (if TSK_DYNAMIC) namerec name; (if TSK_NAMED) } buffer; typedef buffer far *bufferptr; Ctask Manual - Version 2.2 - 90-10-12 - Page 52 The call chain structure The call chain structure is used to link "remove" functions into a chain. This chain is processed when a task group, or the CTask kernel, is removed. It contains a single forward link, and a pointer to the remove function. It also contains a user defined value that can be used by the called remove function. typedef struct callchain_rec far *challchainptr; typedef void (Taskfunc *funcptr_ccp)(callchainptr); typedef struct callchain_rec { callchainptr next; funcptr_ccp func; farptr user_ptr; byte flags; (if TSK_DYNAMIC) } callchain; Ctask Manual - Version 2.2 - 90-10-12 - Page 53 CTask Routines Global Variables int ctask_active Contains 1 if CTask was installed, 0 before the call to install_tasker and after the call to remove_tasker. int tsk_use_ndp Is set to 1 by install_tasker if the NDP configuration option is TRUE and a numeric coprocessor is installed. This variable is used by create_task to determine whether to set the F_USES_NDP task flag. If tsk_use_ndp is nonzero during the call to create_task, the flag is set, causing the NDP state to be saved and restored for this task. You can change this variable to 0 before calling create_task to avoid this. You can also turn on or off the flag individually with tsk_set_flag, but it is usually safer to use the tsk_uses_ndp variable. Setting the F_USES_NDP flag through tsk_set_flag when no coprocessor is present may hang the system. Installation and Removal int install_tasker (int varpri, int speedup, word flags, byteptr name); Installs the multitasker. Must be called prior to any other routine except for secondary kernels. The calling routine is defined as the main task, and assigned the highest priority. To allow other tasks to execute, the main task must have its priority reduced, be delayed, or wait on an event. Returns 1 if CTask was already present in the system, i.e. this is a secondary invocation. Returns 0 if this is the first installation of CTask. "varpri" Enables variable priority if nonzero. Ctask Manual - Version 2.2 - 90-10-12 - Page 54 "speedup" is defined for the IBM PC/XT/AT as the clock tick speedup factor. The timer tick frequency will be set to speedup ticks/sec msecs/tick 0 18.2 54.9 (normal clock) 1 36.4 27.5 2 72.8 13.7 3 145.6 6.9 4 291.3 3.4 Note that all timeouts are specified in tick units, so changing the speedup parameter will influence timeouts and delays. You can enable CLOCK_MSEC in tskconf.h to allow timeouts to be specified in milliseconds. The system clock will not be disturbed by changing the speed. Using values above 2 can lead to interrupt overruns on slower machines and is not recommended. "flags" controls various installation flags through the bitwise OR of the following flags defined in TSK.H: IFL_VIDEO Install INT 10 access resource if set. No protection of Video interrupt if clear. Installation of the Video resource is safer, but may slow down the system noticeably. It is not necessary if you don't do screen-I/O through the BIOS from your CTask program. IFL_DISK Install INT 13 access resource if set. No protection of Disk interrupt if clear. Installation of INT 13 is recommended for better system safety. The resource will allow parallel access to floppy and harddisk, but might be incompatible with some special programs (though none have yet been reported). IFL_INT8_DIR Call original INT 8 directly if set. This changes the timing for the timer inter- rupt. If this flag is clear, the original timer interrupt is chained to through a task, so it can be preempted. If it is set, the original interrupt is chained to directly, at the start of timer interrupt processing. This avoids compatibility problems with certain TSR's and Networks, but may impair CTask operations while those TSR's are active. Ctask Manual - Version 2.2 - 90-10-12 - Page 55 IFL_PRINTER Install INT 17 handler if set. Installation of the printer interrupt handler avoids lengthy busy waiting on printer output, but might be incompatible with certain printer redirectors. IFL_INT15 Install IBM-AT INT 15 handler if set. The IBM INT 15 handler allows avoiding some busy waiting loops. It may, however, be incompatible with some non-100% clones, and with debuggers like Periscope IV. If you're not sure, don't set this flag. IFL_NODOSVARS Do not copy the internal DOS variable area if set. This flag may be used for incompatible versions of DOS or it's clones, but background DOS access will not work if this flag is set. Use only for known incompatible versions, and only if you do not intend to TSR or Spawn. IFL_NOEXITCHECK Don't check for premature exit if set. This flag may be set to disable the standard check for program exit without proper CTask termination. It may be useful in conjunction with MS Windows programs using CTask, since the Windows logic may fool the normal exit check. "name" is the name of the created task group. void remove_tasker (void); Uninstalls the multitasker. Must only be called from the main task, and should be called before exiting the program. int ctask_resident (void); This routine allows checking if another copy of CTask is already resident. It must be called before install_tasker is invoked. Returns 1 if CTask is resident, 0 otherwise. It always returns 1 after install_tasker has been called. Ctask Manual - Version 2.2 - 90-10-12 - Page 56 int link_ctask (void); This routine checks if another copy of CTask is resident, and verifies that the resident copy has a routine stub table to allow code sharing. It must be called before install_tasker is invoked. Returns 1 if a code-sharing copy of CTask is resident, 0 otherwise. It always returns 1 after install_tasker has been called. Searching for names farptr find_name (byteptr name, int kind); This routine searches for a task, group, or event structure from the current task's group downward to the base group. Returns a pointer to the structure, or a pointer to the name record within the structure (depending on kind) if the name was found, LNULL otherwise. This routine may be called before "install_tasker" has been invoked to search names in resident copies. "name" pointer to a zero-terminated, up to eight character, name. Case is significant in names. "kind" is the kind of structure to search for: If -1, all structures are searched, and the first structure with the given name is returned. In this case, the returned pointer points to the name record within the structure, to allow identification of the structure. The "strucp" pointer within that record points to the start of the structure, the "kind" field in the link structure identifies the type of the structure. If kind is >= 0, the returned pointer is a pointer to the start of the structure: TYP_GROUP - Search for Groups only TYP_FLAG - Search for Flags only TYP_RESOURCE - Search for Resources only TYP_COUNTER - Search for Counters only TYP_MAILBOX - Search for Mailboxes only TYP_PIPE - Search for Pipes only TYP_WPIPE - Search for Word Pipes only TYP_BUFFER - Search for Buffers only Ctask Manual - Version 2.2 - 90-10-12 - Page 57 farptr find_group_name (gcbptr group, byteptr name, int kind); Looks for a name in the specified group only. Return value and parameters match those of find_group_name, except "group" pointer to a group control block. Adding names void add_event_name (nameptr elem); Task and event names are normally linked into the name chain automatically on creation. Statically initialised event blocks (events defined with DEF_xxx macros) do not need the create_xxx call, but you have to call add_event_name to link the structure into the name chain. "elem" is a pointer to the "name" field in the event control block. Example: void init_my_flag (void) { static DEF_FLAG(my_flag, "MyFlag"); add_event_name (&my_flag.name); } Remove Functions callchainptr chain_removefunc (funcptr_ccp func, callchainptr chain, farptr user_ptr); Chain a "remove" routine. The remove routine chain is called whenever the group or CTask is removed. It may be used for clean-up work, for example to un-install interrupt handlers. The function enters the routine address passed as parameter into the call chain control block, and chains the block into the remove chain. If dynamic allocation is enabled, the chain pointer may be LNULL. The routine returns the chain pointer, or LNULL if the block could not be allocated. Ctask Manual - Version 2.2 - 90-10-12 - Page 58 Installation example: callchain remchain; chain_removefunc (my_remove_func, &remchain, NULL); The remove routine should have the following form: void Taskfunc my_remove_func (callchainptr chain) { ... /* cleanup */ } For more information, refer to the "Advanced Topics" chapter. void unchain_removefunc (callchainptr chain); Unchain a remove routine from the remove chain. Preemption and Scheduling void preempt_off (void); Disables task preemption. This is the default after instal- lation. With preemption turned off, only delays, event waits, and explicit scheduler calls will cause a task switch. void preempt_on (void); Enables task preemption. Task switches will occur on timer ticks. void tsk_dis_preempt (void) Temporarily disable task preemption. Preemption will be re- enabled by tsk_ena_preempt or an unconditional scheduler call. void tsk_ena_preempt (void) Re-enable task preemption. Note that tsk_dis_preempt and tsk_ena_preempt do not change the global preemption state set by preempt_off and preempt_on. Ctask Manual - Version 2.2 - 90-10-12 - Page 59 void schedule (void); Explicit scheduling request. The highest priority eligible task will be made running. void c_schedule (void); Conditional scheduling request. Scheduling will take place only if preemption is allowed. void yield (void); Explicit scheduling request, with task priority temporarily set to zero. If a task has to wait for some external event in a polling loop, this call may be used to allow tasks of lower priority to execute. The following entry points may be used from assembler routines: extrn _tsk_scheduler: far Direct entry into the scheduler. The stack must be set up as for an interrupt handler, e.g. pushf cli call _tsk_scheduler extrn _sched_int: far Conditional scheduling call. The stack must be set up as for an interrupt handler. This entry should be used by interrupt handlers to cause a reschedule. Interrupt handlers should not use _tsk_schedule. Miscellaneous int tsk_dis_int (void) Disable interrupts. Returns the state of the interrupt flag prior to this call (1 if interrupts were enabled). Ctask Manual - Version 2.2 - 90-10-12 - Page 60 void tsk_ena_int (int state) Enables interrupts if "state" is nonzero. Normally used in conjunction with tsk_dis_int. The routines tsk_dis_int and tsk_ena_int may be used in a simpli- fied scheme with the defines CRITICAL; Declares "int crit_intsav;". C_ENTER; Expands to "crit_intsav = tsk_dis_int ();" C_LEAVE; Expands to "tsk_ena_int (crit_intsav);". void tsk_cli (void) Disables interrupts (intrinsic function). void tsk_sti (void) Unconditionally enables interrupts (intrinsic function). void tsk_outp (int port, byte b) Outputs the value "b" to hardware-port "port" (intrinsic function). byte tsk_inp (int port) Returns the value read from port "port" (intrinsic function). Ctask Manual - Version 2.2 - 90-10-12 - Page 61 Task Operations tcbptr create_task (tcbptr task, funcptr func, byteptr stack, word stksz, word prior, farptr arg [, byteptr name]); Initialises a task. Must be called prior to any other opera- tions on this task. The task is in the stopped state after creation. It must be started to be able to run. If the NDP option is enabled, the F_USES_NDP flag is set in the tcb when the NDP is installed and the global variable tsk_use_ndp is nonzero. Returns a pointer to the created tcb, or LNULL on error. "task" is a pointer to a tcb (LNULL for automatic allo- cation). "func" is a pointer to a void far function, with a single dword sized parameter. "stack" is a pointer to a stack area for the task (LNULL for automatic allocation). "stksz" is the size of the stack area in bytes. "prior" is the tasks priority (0 lowest, 0xffff highest). "arg" is an argument to the created task. It may be used to differentiate between tasks when using the same function in different tasks. "name" is the name of the task, up to eight characters, plus zero-terminator. This parameter is defined only if TSK_NAMEPAR is enabled in tskconf.h. void kill_task (tcbptr task); Kills a task. The task can no longer be used. int start_task (tcbptr task); Starts a task, i.e. makes it eligible for running. Returns 0 if task was started, -1 if the task was not stopped. A value of LNULL for "task" will start the "main task". Ctask Manual - Version 2.2 - 90-10-12 - Page 62 int stop_task (tcbptr task); Stops a task, i.e. removes it from all queues. A value of LNULL for "task" will stop the "main task". Returns 0 on success. int wake_task (tcbptr task); Prematurely wakes a delayed or waiting task. If the task was waiting for an event, it will be removed from the waiting queue, with the operation terminating with an error return value. Returns 0 if task was waked, -1 if the task was not delayed or waiting. A value of LNULL for "task" will wake the "main task". void set_priority (tcbptr task, word prior) Sets the priority of the specified task to "prior". Note that you should NOT modify the priority field in the tcb structure directly. A value of LNULL for "task" will set the priority of the "main task". word get_priority (tcbptr task) Returns the initial priority of the specified task. A value of LNULL for "task" will get the priority of the "main task". void set_task_flags (tcbptr task, byte flags) Sets the flags of the task to "flags". The only flags that can be changed are F_CRIT the task can not be preempted if set F_USES_NDP the task uses the numeric coprocessor Note that you may NOT modify the flag field in the tcb structure directly. A value of LNULL for "task" will set the flags of the "main task". Ctask Manual - Version 2.2 - 90-10-12 - Page 63 void set_funcs (tcbptr task, funcptr save, funcptr rest); Sets the save and restore functions for the specified task. The save function is called whenever the task is deacti- vated, the restore function is called whenever the task is scheduled. This allows saving of critical system states upon a task switch. Both functions are called with a far call, the pointer to the task control block is passed as parameter. A value of LNULL for "task" will set the functions of the "main task". To deactivate one or both functions, pass LNULL as function parameter. See the "Advanced Topics" chapter for more information. farptr set_user_ptr (tcbptr task, farptr uptr); Sets the user pointer in the specified TCB, and returns it's previous value. The user pointer may be used to point to memory blocks local to a task, or to hold other task- specific values. It is never accessed or modified by the CTask kernel. A value of LNULL for "task" will set the user pointer of the "main task". farptr get_user_ptr (tcbptr task); Returns the user pointer of the specified TCB. A value of LNULL for "task" will get the user pointer of the "main task". tcbptr curr_task (void); Returns the pointer to the TCB of the currently running task. Timer Operations Timeouts are normally specified in timer ticks. If CLOCK_MSEC is enabled, timeouts will be converted to the nearest number of timer ticks automatically. word ticks_per_sec (void); Returns a rough estimate of the number of ticks per second even if CLOCK_MSEC is not enabled. Ctask Manual - Version 2.2 - 90-10-12 - Page 64 Event wait Timeouts When waiting for an event, a timeout may be specified. The ope- ration will terminate with an error return value if the timeout is reached before the event occurs. NOTE that the timeout para- meter is not optional. To specify no timeout, use the value 0L. "Tickers" It sometimes is desirable to measure timing intervals or global timeouts without creating special tasks, or while waiting for external events in polling loops. A low overhead way of doing this is the "ticker" structure. When this structure is linked into the ticker chain, the doubleword "ticks" field is decre- mented on every timer tick (in the timer interrupt itself), until it reaches zero. tick_ptr create_ticker (tick_ptr elem, dword val); Links a ticker element into the ticker chain. The ticks field is initialized to "val", and will be decremented to zero. If the elem pointer is LNULL, a new ticker element will be created. Returns the ticker element pointer, LNULL on error. void delete_ticker (tick_ptr elem); Unlinks a ticker element from the ticker chain. Countdown will stop. If the element was allocated dynamically, it will be deleted. void set_ticker (tick_ptr elem, dword val); Sets the ticks field to the given value. If the ticks field is modified directly instead of through this routine, interrupts should be disabled when writing a doubleword value. dword get_ticker (tick_ptr elem) Returns the current ticker value. If the ticks field is read directly instead of through this routine, interrupts should be disabled when reading the doubleword value. Ctask Manual - Version 2.2 - 90-10-12 - Page 65 Delays int t_delay (dword ticks); Delay the current task for "ticks" clock ticks/milliseconds. If ticks is 0, the task is stopped. Returns TIMEOUT if the delay expired, WAKE if the task was activated by wake_task. Timed Events, Watch Events, and Hotkeys You can create timer control blocks, memory/port watch blocks, and keyboard hotkey blocks, to - set a flag - increment or decrement a counter - wake up a task - call a function after a specified timeout interval, or when a certain condition is met. The operation may optionally be repeated. Watch control blocks are checked on every timer tick. They allow memory locations and I/O ports to be checked for a certain value, or for a change in value. When the specified condition is met, the given action is executed. Keyboard hotkeys are checked in the keyboard hardware interrupt. They allow checking for key scan codes and/or keyboard state flag combinations. See the "Advanced Topics" chapter on restrictions placed on functions called by timer/watch/hotkey conditions. Ctask Manual - Version 2.2 - 90-10-12 - Page 66 tlinkptr create_timer_elem (tlinkptr elem, dword tout, farptr strucp, byte kind, byte rept [,dword userpar]); Creates a timer control block, but does not activate it. Returns the address of the control block, LNULL on error. "elem" is the control block to initialise (LNULL for automatic allocation). "tout" specifies the timeout interval. "strucp" points to the structure to be used. This is a flagptr for setting a flag, a counterptr for in/decreasing counters, a tcbptr for waking a task, or a funcptr for calling a function. "kind" gives the kind of structure "strucp" points to. It must be one of TKIND_WAKE for task-wakeup TKIND_PROC for function call TKIND_FLAG for flag set TKIND_COUNTER for counter increment. TKIND_COUNTDEC for counter decrement. "rept" if nonzero, the action will be repeated on every "tout" timeout interval. "userpar" is a doubleword value that can be used by the timeout function if kind is TKIND_PROC. This parameter is optional. NOTE: Timer control blocks can not be named. tlinkptr create_timer (tlinkptr elem, dword tout, farptr strucp, byte kind, byte rept [,dword userpar]); Creates a timer control block and activates it. Returns the address of the control block, LNULL on error. See create_timer_elem above for parameters. If the timeout is zero, the control block is initialized, but is not entered into the timer chain. The timeout must be changed with change_timer for the timer control block to be activated. Ctask Manual - Version 2.2 - 90-10-12 - Page 67 void enable_timer (tlinkptr elem); Activates a timeout element. This call is ignored if the timeout value in the control block is zero. void disable_timer (tlinkptr elem); Disables a timeout element. The element is not deleted. void change_timer (tlinkptr elem, dword tout, byte rept); Changes the timeout value and/or the repeat flag for an existing timer control block. If "tout" is zero, the call has the same effect as disable_timer. void delete_timer (tlinkptr elem); Deletes a timer control block, and removes it from the timeout queue. tlinkptr create_memory_watch_elem (tlinkptr elem, farptr address, word mask, word compare, byte cmpkind, farptr strucp, byte kind, byte rept [, dword userpar]); Creates a memory watch control block. Memory watches compare a byte or word value at the specified address against a comparison value. The value loaded is always a word, the "mask" parameter may be used to restrict comparison to a byte. The watch is not activated. Returns the watch control block pointer, or LNULL on error. "elem" is the control block to initialise (LNULL for automatic allocation). "address" is a pointer to the memory location to watch. "mask" is a bitmask to mask out irrelevant bits before comparison. "compare" is the value the memory contents are to be compared with. Ctask Manual - Version 2.2 - 90-10-12 - Page 68 "cmpkind" is the kind of comparison to be used: TCMP_EQ (*address & mask) == compare TCMP_NE (*address & mask) != compare TCMP_GE (*address & mask) >= compare (unsigned) TCMP_LE (*address & mask) <= compare (unsigned) TCMP_GES (*address & mask) >= compare (signed) TCMP_LES (*address & mask) <= compare (signed) TCMP_CHG Change in value: (*address & mask) != compare compare = *address & mask "strucp" points to the structure to be used. This is a flagptr for setting a flag, a counterptr for in/decreasing counters, a tcbptr for waking a task, or a funcptr for calling a function. "kind" gives the kind of structure "strucp" points to. It must be one of TKIND_WAKE for task-wakeup TKIND_PROC for function call TKIND_FLAG for flag set TKIND_COUNTER for counter increment. TKIND_COUNTDEC for counter decrement. "rept" if nonzero, the action will be repeated whenever the condition is met. "userpar" is a doubleword value that is passed to the watch function if kind is TKIND_PROC. This parameter is optional. NOTE: Watch control blocks can not be named. tlinkptr create_memory_watch (tlinkptr elem, farptr address, word mask, word compare, byte cmpkind, farptr strucp, byte kind, byte rept [, dword userpar]); Creates a memory watch control block and activates it. Returns the watch control block pointer, or LNULL on error. See create_memory_watch_elem for parameters. Ctask Manual - Version 2.2 - 90-10-12 - Page 69 int wait_memory (farptr address, word mask, word compare, byte cmpkind) Delays the current task until the specified condition is met. Parameters are the same as in create_memory_watch. No timeout can be specified. Returns WATCH if the watch condition was met, WAKE if the task was activated by wake_task. tlinkptr create_port_watch_elem (tlinkptr elem, word port, byte in_word, word mask, word compare, byte cmpkind, farptr strucp, byte kind, byte rept [, dword userpar]); Creates a port watch control block. Port watches compare a byte or word value read from the specified port address against a comparison value. The value read is either a word or a byte, depending on the "in_word" parameter. The watch is not activated. Returns the watch control block pointer, or LNULL on error. "elem" is the control block to initialise (LNULL for automatic allocation). "port" is the port address to read. "in_word" Specifies whether a word or byte input instruction is to be used. If zero, a byte is input, if nonzero, a word is read from the port. "mask" is a bitmask to mask out irrelevant bits before comparison. "compare" is the value the port contents are to be compared with. Ctask Manual - Version 2.2 - 90-10-12 - Page 70 "cmpkind" is the kind of comparison to be used: TCMP_EQ (in(port) & mask) == compare TCMP_NE (in(port) & mask) != compare TCMP_GE (in(port) & mask) >= compare (unsigned) TCMP_LE (in(port) & mask) <= compare (unsigned) TCMP_GES (in(port) & mask) >= compare (signed) TCMP_LES (in(port) & mask) <= compare (signed) TCMP_CHG Change in value: (in(port) & mask) != compare compare = in(port) & mask (NOTE: The port is read only once.) "strucp" points to the structure to be used. This is a flagptr for setting a flag, a counterptr for in/decreasing counters, a tcbptr for waking a task, or a funcptr for calling a function. "kind" gives the kind of structure "strucp" points to. It must be one of TKIND_WAKE for task-wakeup TKIND_PROC for function call TKIND_FLAG for flag set TKIND_COUNTER for counter increment. TKIND_COUNTDEC for counter decrement. "rept" if nonzero, the action will be repeated whenever the condition is met. "userpar" is a doubleword value that is passed to the watch function if kind is TKIND_PROC. This parameter is optional. NOTE: Watch control blocks can not be named. tlinkptr create_port_watch (tlinkptr elem, word port, byte in_word, word mask, word compare, byte cmpkind, farptr strucp, byte kind, byte rept [, dword userpar]); Creates a port watch control block and activates it. Returns the watch control block pointer, or LNULL on error. See create_port_watch_elem for parameters. Ctask Manual - Version 2.2 - 90-10-12 - Page 71 int wait_port (word port, byte in_word, word mask, word compare, byte cmpkind) Delays the current task until the specified condition is met. Parameters are the same as in create_port_watch. No timeout can be specified. Returns WATCH if the watch condition was met, WAKE if the task was activated by wake_task. void enable_watch (tlinkptr elem); The specified watch element is activated. void disable_watch (tlinkptr elem); The specified watch element is deactivated. The element is not deleted. void delete_watch (tlinkptr elem); The specified watch element is removed. NOTE: delete_timer, delete_watch, and change_timer should not be used on automatically allocated timer/watch control blocks. Since such blocks are deallocated once the timeout expires or the condition is met (except for repeat operations), the validity of the pointer is not guaranteed. tlinkptr create_hotkey_elem (tlinkptr elem, byte scancode, byte mask1, byte flag1, byte mask2, byte flag2, byte mask3, byte flag3, farptr strucp, byte kind, byte rept [, dword userpar]); Creates a keyboard hotkey control block. Keyboard hotkeys compare the scancode and/or the BIOS keyboard flags against the given values. The flag fields are masked before comparing. The hotkey is not activated. The file "kbd.h" contains definitions for scan codes and flag byte values. Ctask Manual - Version 2.2 - 90-10-12 - Page 72 Returns the hotkey control block pointer, or LNULL on error. CAUTION: In contrast to the timer/watch creation functions, this function does not accept a LNULL parameter for the element to create. Dynamic allocation can not be used in an interrupt handler, and a temporary element would have to be released in the keyboard interrupt. Therefore, the hotkey control block must always be static. "elem" is the control block to initialise. This pointer must NOT be LNULL. "scancode" is the keyboard scancode to look for. If scancode is 0, only the flag values are compared. "flag1..3" are the values the BIOS keyboard flags are to be compared with. "mask1..3" are bitmasks to mask out irrelevant bits before comparing the flag values. Set both mask and flag to 0 to disable comparison. "strucp" points to the structure to be used. This is a flagptr for setting a flag, a counterptr for in/decreasing counters, a tcbptr for waking a task, or a funcptr for calling a function. "kind" gives the kind of structure "strucp" points to. It must be one of TKIND_WAKE for task-wakeup TKIND_PROC for function call TKIND_FLAG for flag set TKIND_COUNTER for counter increment. TKIND_COUNTDEC for counter decrement. "rept" if nonzero, the action will be repeated whenever the hotkey is activated. "userpar" is a doubleword value that is passed to the hotkey function if kind is TKIND_PROC. This parameter is optional. NOTE: Hotkey control blocks can not be named. Ctask Manual - Version 2.2 - 90-10-12 - Page 73 tlinkptr create_hotkey_entry (tlinkptr elem, byte scancode, byte mask1, byte flag1, byte mask2, byte flag2, byte mask3, byte flag3, farptr strucp, byte kind, byte rept [, dword userpar]); Creates a keyboard hotkey control block and enables it. Returns the hotkey control block pointer, or LNULL on error. See create_hotkey_elem for parameters. int wait_hotkey (byte scancode, byte mask1, byte flag1, byte mask2, byte flag2, byte mask3, byte flag3) Delays the current task until the specified hotkey is hit. Parameters are the same as in create_hotkey_entry. No timeout can be specified. Returns WATCH if the hotkey was hit, WAKE if the task was activated by wake_task. void enable_hotkey (tlinkptr elem); The specified hotkey element is activated. void disable_hotkey (tlinkptr elem); The specified hotkey element is deactivated. The element is not deleted. void delete_hotkey (tlinkptr elem); The specified hotkey entry is removed. Ctask Manual - Version 2.2 - 90-10-12 - Page 74 Event Operations Resources A Resource is either in use or free, the default state is free. If a task has requested a resource, its state is in use, and the requesting task is said to "own" the resource. Tasks requesting a resource while it is in use will be made waiting. If the resource is released, the highest priority waiting task is made eligible, and is assigned the resource. Interrupt handlers may not use resource functions other than "check_resource". To facilitate use of resources in nested routines, CTask allows a resource to be requested by a Task already owning it. Different calls may be used to request resources, depending on how such nested calls should be handled. The standard request_resource and c_request_resource calls just mark the resource as in use by setting the owner count to 1, and the first nested routine that releases the resource will cause the resource to be freed. The request_cresource and c_request_cresource calls increment the owner count, so the resource will only be freed upon a matching count of requests and releases. resourceptr create_resource (resourceptr rsc [, byteptr name]); This initialises a resource. Must be used prior to any other operations on a resource. Returns the address of the control block, LNULL on error. "rsc" is the resource control block (LNULL for automatic allocation). "name" is the name of the resource, up to eight characters, plus zero-terminator. This parameter is defined only if TSK_NAMEPAR is enabled in tskconf.h. Ctask Manual - Version 2.2 - 90-10-12 - Page 75 DEF_RESOURCE(var,name) This macro defines and initialises a resource control block at compile time. It can replace the run-time call to create_resource. However, the created block is not linked into the name chain. To make the block visible, you must use add_event_name. Most compilers will not allow aggregate initialisers of automatic variables, so you must use this definition with the static attribute inside routines. "var" is the variable name to define. "name" is the name of the resource. It can be a zero length string, but it must not be LNULL. Since this is a macro, you must give the parameter even when TSK_NAMEPAR is disabled. void delete_resource (resourceptr rsc); Calling this routine is optional. It will kill all tasks waiting for the resource. void release_resource (resourceptr rsc); Decrement the owner count, and release the resource if it is zero. If the task does not own the resource, the call is ignored. If the resource is released, and tasks are waiting for access, the highest priority task will gain access to the resource. int request_resource (resourceptr rsc, dword timeout); Requests the resource. If it is not available, the task is suspended. A timeout may be specified. Returns 0 if resource was allocated, TIMEOUT if a timeout occurred, WAKE on wake. This call is ignored (returns a 0) if the calling task already owns the resource. Ctask Manual - Version 2.2 - 90-10-12 - Page 76 int request_cresource (resourceptr rsc, dword timeout); Requests the resource. If it is not available, the task is suspended. A timeout may be specified. Returns 0 if resource was allocated, TIMEOUT if a timeout occurred, WAKE on wake. This call increments the owner count, and returns 0, if the calling task already owns the resource. int c_request_resource (resourceptr rsc); Requests the resource only if it is available. Returns 0 if resource was allocated, -1 if unavailable. int check_resource (resourceptr rsc); Returns 0 if resource is allocated, 1 if free. Flags A Flag can be either on or off, the default state is off (0). Tasks can wait on either state of the flag. If the state is changed, all tasks waiting for the state are made eligible. Interrupt handlers may use the "set_flag", "clear_flag", and "check_flag" functions. flagptr create_flag (flagptr flg [, byteptr name]); This initialises a flag. Must be used prior to any other operations on a flag. The state is set to 0. Returns the address of the control block, LNULL on error. "flg" is the flag control block (LNULL for automatic allocation). "name" is the name of the flag, up to eight characters, plus zero-terminator. This parameter is defined only if TSK_NAMEPAR is enabled in tskconf.h. Ctask Manual - Version 2.2 - 90-10-12 - Page 77 DEF_FLAG(var,name) This macro defines and initialises a flag control block at compile time. It can replace the run-time call to create_flag. However, the created block is not linked into the name chain. To make the block visible, you must use add_event_name. Most compilers will not allow aggregate initialisers of automatic variables, so you must use this definition with the static attribute inside routines. "var" is the variable name to define. "name" is the name of the flag. It can be a zero length string, but it must not be LNULL. Since this is a macro, you must give the parameter even when TSK_NAMEPAR is disabled. void delete_flag (flagptr flg); Calling this routine is optional. It will kill all tasks waiting for the flag. void set_flag (flagptr flg); This sets the flag. All tasks waiting for the set state will be made eligible for running. void clear_flag (flagptr flg); This clears the flag. All tasks waiting for the clear state will be made eligible for running. int wait_flag_set (flagptr flg, dword timeout); Waits for the set state of the flag. If the flag is not set, the task is suspended. A timeout may be specified. Returns 0 if the flag was set, TIMEOUT on timeout, WAKE on wake. int wait_flag_clear (flagptr flg, dword timeout); Waits for the clear state of the flag. If the flag is not clear, the task is suspended. A timeout may be specified. Returns 0 if the flag was cleared, TIMEOUT on timeout, WAKE on wake. Ctask Manual - Version 2.2 - 90-10-12 - Page 78 int clear_flag_wait_set (flagptr flg, dword timeout) Combines the operations clear_flag and wait_flag_set. Returns 0 if the flag was set, TIMEOUT on timeout, WAKE on wake. int check_flag (flagptr flg); Returns 0 if flag clear, 1 if set. Counters A Counter can have any value from 0L to 0xffffffffL, the default value is 0. Tasks can wait for a counter being zero or non-zero. If the counter is cleared or decremented to zero, all tasks wai- ting for the zero condition are made eligible. If the counter is incremented, the highest priority task waiting for non-zero is made eligible, and the counter is decremented by one. Interrupt handlers may use the "clear_counter", "inc_counter", "dec_counter", "set_counter", and "check_counter" functions. counterptr create_counter (counterptr cnt [, byteptr name]); This initialises a counter. Must be used prior to any other operations on a flag. The value is set to 0. Returns the address of the control block, LNULL on error. "cnt" is the counter control block (LNULL for automatic allocation). "name" is the name of the counter, up to eight characters, plus zero-terminator. This parameter is defined only if TSK_NAMEPAR is enabled in tskconf.h. Ctask Manual - Version 2.2 - 90-10-12 - Page 79 DEF_COUNTER(var,name) This macro defines and initialises a counter control block at compile time. It can replace the run-time call to create_counter. However, the created block is not linked into the name chain. To make the block visible, you must use add_event_name. Most compilers will not allow aggregate initialisers of automatic variables, so you must use this definition with the static attribute inside routines. "var" is the variable name to define. "name" is the name of the counter. It can be a zero length string, but it must not be LNULL. Since this is a macro, you must give the parameter even when TSK_NAMEPAR is disabled. void delete_counter (counterptr cnt); Calling this routine is optional. It will kill all tasks waiting for the counter. void clear_counter (counterptr cnt); Clears the counter to zero. All tasks waiting for the zero state will be made eligible for running. int wait_counter_set (counterptr cnt, dword timeout); Waits for the counter having a nonzero value. If the value is zero, the task is suspended. The value is decremented when the task gets access to the counter. A timeout may be specified. Returns 0 if the counter was nonzero, TIMEOUT on timeout, WAKE on wake. int wait_counter_clear (counterptr cnt, dword timeout); Waits for the counter having a zero value. If the value is nonzero, the task is suspended. A timeout may be specified. Returns 0 if the counter was zero, TIMEOUT on timeout, WAKE on wake. Ctask Manual - Version 2.2 - 90-10-12 - Page 80 dword inc_counter (counterptr cnt); Increments the counter. If tasks are waiting for the nonzero state, the highest priority task is given access to the counter. Returns the new value of the counter. dword dec_counter (counterptr cnt); Decrements the counter unless it is already zero. If the counter is decremented to zero, all tasks waiting for the zero state are made eligible. Returns the new value of the counter. void set_counter (counterptr cnt, dword val); Sets the counter to the given value. If "val" is nonzero, and tasks are waiting for the set state, the highest priority tasks are made eligible, and "val" is decremented, until either "val" reaches zero, or there are no more tasks waiting. If val is, or is counted down to, zero, all tasks waiting for the zero state are made eligible. dword check_counter (counterptr cnt); Returns the current value of the counter. Mailboxes A Mailbox can hold any number of mail blocks. Tasks can send mail to a mailbox and wait for mail to arrive. A mail block is assigned to the highest priority waiting task. Care must be exercised not to re-use a mail block until it has been processed by the receiving task. The mail block format is user defineable, with the first doubleword in a block reserved for the tasking system. Interrupt handlers may use the "send_mail", "c_wait_mail", and "check_mailbox" functions. Note that mailboxes are well suited to provide the mechanism for managing a chain of (equally sized) free mail blocks. On initialization, all free blocks would be "sent" to the manager box. Requesting a free block would use "wait_mail", and freeing a used block would again "send" it to the manager mailbox. Ctask Manual - Version 2.2 - 90-10-12 - Page 81 mailboxptr create_mailbox (mailboxptr box [, byteptr name]); This initialises a mailbox. Must be used prior to any other operations on a mailbox. Returns the address of the control block, LNULL on error. "box" is the mailbox control block (LNULL for automatic allocation). "name" is the name of the mailbox, up to eight characters, plus zero-terminator. This parameter is defined only if TSK_NAMEPAR is enabled in tskconf.h. DEF_MAILBOX(var,name) This macro defines and initialises a mailbox control block at compile time. It can replace the run-time call to create_mailbox. However, the created block is not linked into the name chain. To make the block visible, you must use add_event_name. Most compilers will not allow aggregate initialisers of automatic variables, so you must use this definition with the static attribute inside routines. "var" is the variable name to define. "name" is the name of the mailbox. It can be a zero length string, but it must not be LNULL. Since this is a macro, you must give the parameter even when TSK_NAMEPAR is disabled. void delete_mailbox (mailboxptr box); Calling this routine is optional. It will kill all tasks waiting for mail. void send_mail (mailboxptr box, farptr msg); Sends a message to the specified mailbox. If tasks are waiting for mail, the highest priority task will get it. farptr wait_mail (mailboxptr box, dword timeout); Waits for mail. If no mail is available, the task is suspended. A timeout may be specified. Returns the pointer to the received mail block, TTIMEOUT on timeout, TWAKE on wake. Ctask Manual - Version 2.2 - 90-10-12 - Page 82 farptr c_wait_mail (mailboxptr box); Reads mail only if mail is available. Returns LNULL if there is no mail, else a pointer to the received message. int check_mailbox (mailboxptr box); Returns 0 if mailbox is empty, 1 otherwise. Pipes A Pipe has a buffer to hold character or word sized items. An item may be written to a pipe if there is space in the buffer. Otherwise, the writing task will be made waiting. A reading task will be made waiting if the buffer is empty. If an item has been read, the highest priority task waiting to write to the pipe will be allowed to write. Interrupt handlers may only use pipe functions "check_pipe", "c_write_pipe", and "c_read_pipe". Note that the values -1 and -2 (0xffff and 0xfffe) should be avoided when writing to word pipes. These values are used to mark timeout and wake when reading, or pipe empty when checking a word pipe, and thus may lead to erroneous operation of your routines. pipeptr create_pipe (pipeptr pip, farptr buf, word bufsize [, byteptr name]); wpipeptr create_wpipe (wpipeptr pip, farptr buf, word bufsize [, byteptr name]); This initialises a pipe. Must be used prior to any other operations on a pipe. "bufsize" specifies the buffer size in bytes. With word pipes, the buffer size should be divisible by two. Returns the address of the control block, LNULL on error. "pip" is the pipe/wpipe control block (LNULL for automatic allocation). "buf" is a pointer to the pipe buffer. "bufsize" is the size of the buffer in bytes. "name" is the name of the pipe, up to eight characters, plus zero-terminator. This parameter is defined only if TSK_NAMEPAR is enabled in tskconf.h. Ctask Manual - Version 2.2 - 90-10-12 - Page 83 DEF_PIPE(var,name,buf,bufsize) DEF_WPIPE(var,name,buf,bufsize) This macro defines and initialises a pipe/word pipe control block at compile time. It can replace the run-time call to create_pipe/create_wpipe. However, the created block is not linked into the name chain. To make the block visible, you must use add_event_name. Most compilers will not allow aggregate initialisers of automatic variables, so you must use this definition with the static attribute inside routines. "var" is the variable name to define. "name" is the name of the pipe. It can be a zero length string, but it must not be LNULL. Since this is a macro, you must give the parameter even when TSK_NAMEPAR is disabled. "buf" is a pointer to the pipe buffer. "bufsize" is the size of the buffer in bytes. void delete_pipe (pipeptr pip); void delete_wpipe (wpipeptr pip); Calling this routine is optional. It will kill all tasks waiting to read or write messages. int read_pipe (pipeptr pip, dword timeout); word read_wpipe (wpipeptr pip, dword timeout); Read an item from a pipe. If no item is available, the task is suspended. A timeout may be specified. Returns the item, or TIMEOUT on timeout, WAKE on wake. int c_read_pipe (pipeptr pip); word c_read_wpipe (wpipeptr pip); Reads an item from a pipe only if one is available. Returns the received item, or -1 if none is available. Ctask Manual - Version 2.2 - 90-10-12 - Page 84 int write_pipe (pipeptr pip, byte ch, dword timeout); int write_wpipe (wpipeptr pip, word ch, dword timeout); Writes an item to a pipe. If the buffer is full, the task is suspended. A timeout may be specified. If tasks are waiting to read, the item will be assigned to the highest priority waiting task. Returns 0 on success, or TIMEOUT on timeout, WAKE on wake. int c_write_pipe (pipeptr pip, byte ch); int c_write_wpipe (wpipeptr pip, word ch); Writes an item to a pipe only if enough space is available. Returns 0 on success, or -1 if no space available. int wait_pipe_empty (pipeptr pip, dword timeout); int wait_wpipe_empty (wpipeptr pip, dword timeout); Waits for the pipe to be emptied. If the pipe is already empty on entry, the task continues to run. Returns 0 on empty, TIMEOUT on timeout, WAKE on wake. int check_pipe (pipeptr pip); word check_wpipe (pipeptr pip); Returns -1 if the pipe is empty, else the first item in the pipe. The item is not removed from the pipe. word pipe_free (pipeptr pip); word wpipe_free (wpipeptr pip); Returns the number of free items available in the pipe. void flush_pipe (pipeptr pip) void flush_wpipe (wpipeptr pip) Clears the pipe. Tasks waiting for the empty state are made eligible. Ctask Manual - Version 2.2 - 90-10-12 - Page 85 Buffers A Buffer has a buffer to hold message strings. A message may be written to a buffer if it fits into the buffer. Otherwise, the writing task will be made waiting. A reading task will be made waiting if the buffer is empty. If a message has been read, the highest priority task waiting to write to the buffer will be allowed to write if its message fits into the available space. Interrupt handlers may not use buffer functions other than "check_buffer". The buffer routines are implemented using resources and pipes, and thus are not part of the true "kernel" routines. There is no static creation macro for buffers. bufferptr create_buffer (bufferptr buf, farptr pbuf, word bufsize [, byteptr name]); This initialises a buffer. Must be used prior to any other operations on a buffer. The minimum buffer size is the length of the longest expected message plus two. Returns the address of the control block, LNULL on error. "buf" is the buffer control block (LNULL for automatic allocation). "pbuf" is a pointer to the buffer. "bufsize" is the size of the buffer in bytes. "name" is the name of the buffer, up to eight characters, plus zero-terminator. This parameter is defined only if TSK_NAMEPAR is enabled in tskconf.h. void delete_buffer (bufferptr buf); Calling this routine is optional. It will kill all tasks waiting to read or write messages. Ctask Manual - Version 2.2 - 90-10-12 - Page 86 int read_buffer (bufferptr buf, farptr msg, int size, dword timeout); Read a message from a buffer. If no message is available, the task is suspended. A timeout may be specified. The message will be copied to the buffer "buf", with a maximum length of "size" bytes. Returns the length of the received message, TIMEOUT on timeout, WAKE on wake. int c_read_buffer (bufferptr buf, farptr msg, int size); Reads a message from a buffer only if one is available. Returns the length of the received message, or -1 if none is available. int write_buffer (bufferptr buf, farptr msg, int size, dword timeout); Writes a message from "msg" with length "size" to a buffer. If not enough space for the message is available, the task is suspended. A timeout may be specified. If tasks are waiting for messages, the highest priority task will get it. Returns the length of the message, TIMEOUT on timeout, WAKE on wake, -3 on error (length < 0 or length > buffer size). int c_write_buffer (bufferptr buf, farptr msg, int size); Writes a message to a buffer only if enough space is available. Returns the length of the message, -1 if no space available, or -3 on error (length < 0 or length > buffer size). word check_buffer (bufferptr buf); Returns the current number of bytes (not messages) in the buffer, including the length words. Ctask Manual - Version 2.2 - 90-10-12 - Page 87 The Keyboard Handler word t_read_key (void) Waits for a key to be entered. Returns the ASCII-code in the lower byte, and the scan-code in the upper byte, or WAKE (0xfffe) on wake. word t_wait_key (dword timeout) Waits for a key to be entered. Returns the ASCII-code in the lower byte, and the scan-code in the upper byte, or TIMEOUT (0xffff) on timeout, WAKE (0xfffe) on wake. word t_keyhit (void) Returns -1 (0xffff) if no key was entered, else the value of the key. The key is not removed. The Serial I/O handler The serial I/O handler provides full duplex interrupt driven I/O on the serial ports. Support for COM1 and COM2 is included, adding other ports is possible by changing the source and/or defining ports on-line. int v24_define_port (int base, byte irq, byte vector) Defines a new COM-port. This routine can only be used if TSK_DYNAMIC is enabled. "base" is the port base I/O address. "irq" is the IRQ-line number (0-7 for XT, 0-15 for AT) the port uses for interrupts. "vector" is the interrupt vector number (0-0xff). The return value is the internal port number for use with v24_install. -1 is returned on error (memory full). Ctask Manual - Version 2.2 - 90-10-12 - Page 88 sioptr v24_install (int port, int init, farptr rcvbuf, word rcvsize, farptr xmitbuf, word xmitsize); Installs the handler for the specified port. Currently, ports 0 (COM1) and 1 (COM2) are supported by default. Both ports may be used simultaneously, the buffer areas for the ports must not be shared. "rcvbuf" is a word pipe buffer area for received characters. May be LNULL for automatic allocation. "rcvsize" specifies the receive buffer size in bytes. Note that the buffer will hold rcvsize / 2 received characters. "xmitbuf" is a byte pipe buffer for characters waiting for transmission. May be LNULL for automatic allocation. "xmitsize" gives the transmit buffer size in bytes. "port" Port number to install (0: COM1, 1: COM2). If the port number is ORed with 0x80, the port is *relative*. This means that the entry in the BIOS table for COM-Ports is used to search the tables internal to the driver for the port information, instead of using the table entry directly. If the port address cannot be found, the driver returns with an error code. Note that ports are numbered from 0, so to specify relative COM1, pass 0x80 as parameter. "init" if non-zero, the port is initialised with the default values specified in the source. If the parameter is zero, the control registers and baud rates on entry are not modified. The return value is a pointer to the sio control block for use with the other driver routines. LNULL is returned on error (invalid port number, bad buffer sizes, nonexistent hardware, out of memory). Ctask Manual - Version 2.2 - 90-10-12 - Page 89 void v24_remove (sioptr sio, int restore); Removes the driver for the specified control block. Should be called for all ports installed before exiting the program. If the "restore" parameter is nonzero, the control registers and the baud rate that were set before installation of the driver are restored. If the parameter is zero, the values are not changed. void v24_remove_all (void) Removes all installed serial i/o drivers. This routine is automatically called on remove_tasker if drivers were installed. Note that you can not specify a restore parameter, the default restore parameter is used (constant in tsksio.c). void v24_change_rts (sioptr sio, int on); Changes the state of the RTS output line. A nonzero value for "on" will turn the output on. void v24_change_dtr (sioptr sio, int on); Changes the state of the DTR output line. A nonzero value for "on" will turn the output on. void v24_change_baud (sioptr sio, long rate); Changes the baud rate. The following baud rates are suppor- ted: 50, 75, 110, 134, 150, 300, 600, 1200, 1800, 2000, 2400, 3600, 4800, 7200, 9600, 19200, 38400. Note that baud rates above 9600 may cause problems on slow machines. Ctask Manual - Version 2.2 - 90-10-12 - Page 90 void v24_change_parity (sioptr sio, int par); Changes parity. The parameter must be one of the following values defined in "sio.h": PAR_NONE no parity checks PAR_EVEN even parity PAR_ODD odd parity PAR_MARK mark parity PAR_SPACE space parity void v24_change_wordlength (sioptr sio, int len); Changes word length. Values 5, 6, 7, 8 may be given. void v24_change_stopbits (sioptr sio, int n); Changes Stopbits. Values 1 and 2 are allowed. void v24_watch_modem (sioptr sio, byte flags); Watches the modem status lines to control transmission. "flags" Specifies the input lines that must be active to allow transmission. Transmission will stop if one of the lines goes inactive. The parameter may be combined from the following values defined in "sio.h": CTS to watch clear to send DSR to watch data set ready RI to watch ring indicator CD to watch carrier detect A value of zero (the default) will allow transmission regardless of modem status. Ctask Manual - Version 2.2 - 90-10-12 - Page 91 void v24_protocol (sioptr sio, int prot, word offthresh, word onthresh); Sets the handshake protocol to use. "prot" specifies the protocol. This parameter may be combined from the following values: XONXOFF to enable XON/XOFF (DC1/DC3) handshake RTSCTS to enable RTS/CTS handshake "offthresh" specifies the minimum number of free items in the receive buffer. If this threshold is reached, an XOFF is transmitted and/or the RTS line is inactivated. "onthresh" specifies the minimum number of items that must be free before XON is transmitted and/or the RTS line is re-activated. Enabling XONXOFF will remove all XON and XOFF characters from the input stream. Transmission will be disabled when XOFF is received, and re-enabled when XON is received. Enabling RTSCTS will stop transmission when the CTS modem input line is inactive. int v24_send (sioptr sio, byte ch, dword timeout); Transmits the character "ch". A timeout may be specified. Returns TIMEOUT on timeout, WAKE on wake, else 0. int v24_receive (sioptr sio, dword timeout); Waits for a received character. A timeout may be specified. Returns TIMEOUT on timeout, WAKE on wake, else the character in the lower byte, plus an error code in the upper byte. The error code is the combination of 0x02 overrun error 0x04 parity error 0x08 framing error 0x10 break interrupt. int v24_check (sioptr sio); Returns -1 if no receive character is available, else the next character from the pipe. The character is not removed. Ctask Manual - Version 2.2 - 90-10-12 - Page 92 int v24_overrun (sioptr sio); Checks for receive pipe overrun. Returns 1 if an overrun occurred, 0 otherwise. Clears the overrun flag. int v24_modem_status (sioptr sio); Returns the current modem status word. The CTS, DSR, RI, and CD defines may be used to extract the modem input line status. int v24_complete (sioptr sio); Returns 1 if all characters in the transmit pipe have been sent, else 0. int v24_wait_complete (sioptr sio, dword timeout); Waits for the transmit pipe to be empty. Returns TIMEOUT on timeout, WAKE on wake, else 0. void v24_flush_receive (sioptr sio); Flushes the receive pipe. void v24_flush_transmit (sioptr sio) Flushes the transmit pipe. Tasks waiting for transmit completion are made eligible. Ctask Manual - Version 2.2 - 90-10-12 - Page 93 The Printer Output Driver The printer output driver provides for buffered output to up to three printer ports (more can be added by editing the source). Interrupt or polling may be selected. Due to the usual hardware implementation of printers and the printer interface, using polling is recommended. When using interrupts, you should not simultaneously install both port 0 and port 1 with interrupt enabled, since both ports share the same interrupt line. int prt_install (int port, byte polling, word prior, farptr xmitbuf, word xmitsize); Installs the printer driver for the specified port. Ports 0 (LPT1), 1 (LPT2), and 2 (LPT3) are supported. "port" The output port to use. If the port number is ORed with 0x80, the port is relative. This means that the entry in the BIOS table for LPT-Ports is used to search the tables internal to the driver for the port information, instead of using the table entry directly. If the port address cannot be found, the driver returns with an error code. Note that ports are numbered from 0, so to specify LPT1, pass 0x80 as parameter. "polling" specifies polling output when nonzero, interrupt output when zero. "prior" sets the priority of the printer output task. "xmitbuf" is a buffer area for the printer output buffer. May be LNULL for automatic allocation. "xmitsize" specifies the output buffer size in bytes. The return value is the internal port number for use with the other driver routines. -1 is returned on error (invalid port number, bad buffer sizes, nonexistent hardware). void prt_remove (int port); Removes the printer driver for the specified port. Ctask Manual - Version 2.2 - 90-10-12 - Page 94 void prt_remove_all (void) Removes all installed printer ports. This routine is automatically called on remove_tasker if ports were installed. void prt_change_control (int port, byte control); Changes the printer control output lines of the port. The value for "control" may be combined from the following values defined in "prt.h": AUTOFEED will enable printer auto feed if set INIT will initialise (prime) the printer if clear SELECT will select the printer if set int prt_write (int port, byte ch, dword timeout); Write a byte to the printer. A timeout may be given. Returns 0 on success, TIMEOUT on timeout, WAKE on wake. int prt_status (int port); Returns the current printer status lines, combined from the values BUSY Printer is busy when 0 ACK Acknowledge (pulsed 0) PEND Paper End detected when 0 SELIN Printer is selected (on line) when 1 ERROR Printer error when 0 int prt_complete (int port); Returns 1 if the printer buffer has been completely transmitted, 0 otherwise. int prt_wait_complete (int port, dword timeout); Waits for printer output to complete. Returns 0 on success, else TIMEOUT on timeout, WAKE on wake. void prt_flush (int port) Flushes the output pipe of the printer. Tasks waiting for print completion are made eligible. Ctask Manual - Version 2.2 - 90-10-12 - Page 95 Support Modules Memory Allocation Interface The file tskalloc.c contains routines that interface CTask to the standard C memory allocation routines. Since the CTask kernel is model independent, it can not use the runtime routines directly. Also, to avoid crashes, CTask routines allocating memory must use a resource to channel access to the memory allocator, since the standard routines are not reentrant. All memory allocation in tasks should use the CTask allocation functions instead of the standard ones. See the chapter on memory allocation for more information. farptr tsk_alloc (word size); Replacement function for the standard malloc. farptr tsk_calloc (word item, word size); Replacement function for the standard calloc. farptr tsk_free (farptr item); Replacement function for the standard free. This routine always returns LNULL. farptr tsk_realloc (farptr item, word size); Replacement function for the standard realloc. Global variables: resource alloc_resource; Is the memory allocation routine access resource. If you use other allocator routines, or want to allocate several items in a row, you may enclose the calls to the standard C functions in calls to request_resource (&alloc_resource) and free_resource (&alloc_resource). Ctask Manual - Version 2.2 - 90-10-12 - Page 96 Printf Replacements Version 2.1 adds several functions that can (at least in most cases) replace the standard C printf family functions. Apart from being a lot faster and smaller, the routines do not assume DS==SS, are reentrant and completely self-contained, and thus can be used independent of the memory model in use. They use no CTask kernel functions, and could also be used in non-CTask applications, for example in Assembler modules, or device drivers/DLLs for DOS and Windows. The routines support direct access to the secondary screen in a dual monitor system. int tsk_sprintf (farptr str, farptr fmt, ...); int tsk_vsprintf (farptr str, farptr fmt, farptr arg); Print to string. Replacement for sprintf and vsprintf. Returns number of character written, not counting the terminating zero character. void tsk_rprintf (farptr fmt, ...); void tsk_vrprintf (farptr fmt, farptr arg); Output directly to screen regen hardware buffer. Allows printing to the secondary monitor in dual-screen systems, and is extremely fast. void tsk_printf (farptr fmt, ...); void tsk_vprintf (farptr fmt, farptr arg); Print to console. Uses INT 10 calls, so it's faster than standard printf, but can't be redirected. void tsk_fprintf (int handle, farptr fmt, ...); void tsk_vfprintf (int handle, farptr fmt, farptr arg); Print to file. Note that this is no direct replacement for fprintf/vfprintf, since the parameter is a DOS file handle, not a FILE *. Use with files opened through the low-level open functions, or use the standard fileno() function to get the handle of a stream file. Stream files should be flushed before use if other C functions were used to write to the file. void tsk_putc (char c); Put character to screen using INT 10. Ctask Manual - Version 2.2 - 90-10-12 - Page 97 void tsk_puts (farptr str); Put string to screen using INT 10. A new line is started after output. void tsk_rputc (char c); Put character directly to screen hardware regen buffer. void tsk_rputs (farptr str); Put string directly to screen hardware regen buffer. A new line is started after output. word tsk_set_dualdis (void); Initialize the hardware regen output to go to the secondary monitor. Returns the regen buffer address, or 0 if no secondary adapter was found. word tsk_set_currdis (void); Initialize the hardware regen output to go to the primary monitor. Returns the regen buffer address, or 0 on error. void tsk_set_colour (int rows, int cols); Initialize the hardware regen output to go to the colour monitor with the given number of screen rows and columns. void tsk_set_mono (int rows, int cols); Initialize the hardware regen output to go to the monochrome monitor with the given number of screen rows and columns. Ctask Manual - Version 2.2 - 90-10-12 - Page 98 void tsk_set_regen (int regenseg, int port, int rows, int cols); Initialize the hardware regen output to go to the specified monitor address. You have to specify regenseg The segment address of the regen buffer. port The 6845 display controller port. If zero, you can still write to the screen, but the cursor will not be moved. rows The number of rows on screen. cols The number of columns on screen. Note that you can use this function to restrict output to a smaller part of the screen by increasing the segment address and decreasing the number of rows. void tsk_setpos (int row, int col); Set the cursor position for hardware output. Row and column are numbered starting at 0. void tsk_set_attr (int attr); Set the screen display attribute byte for subsequent hardware output to "attr". Global variables: dword tsk_regen; word tsk_regen_o; word tsk_regen_s; Contain the current hardware screen pointer. tsk_regen_o contains the current offset, tsk_regen_s the regen buffer segment. tsk_regen is a synonym for doubleword access to both variables. word tsk_disport; The hardware 6845 controller port address. If set to 0, the display cursor will not be updated. Ctask Manual - Version 2.2 - 90-10-12 - Page 99 Snapshot Dump The snapshot dump module TSKSNAP.C provides a display of the current state of tasks and control structures. This display is rather extensive, and can easily exceed screen capacity. It may be useful to change the routines to suit your needs by omitting some of the information, or displaying other than the standard info. Since display of the snapshot runs at high priority, the system will slow down noticeably if snapshots are output with high frequency. The standard routines provided are void screensnap (int rows); Output to hardware screen regen buffer. The hardware screen must have been initialised with a call to the tsk_set_dualdis or similar functions (see description of printf replacements). If the "rows" parameter is nonzero, the display will be truncated at the given number of rows. void csnapshot (void); Output to console using INT 10. void snapshot (FILE *f); Output to the given stream file. Ctask Manual - Version 2.2 - 90-10-12 - Page 100 Advanced Topics Primary and Secondary Kernels Version 2.0 officially introduced support for CTask programs going TSR and spawning. Version 2.1 adds some features to make this safer (especially in EMS systems), and to save code in secondary applications. The manual often refers to the terms "primary" and "secondary" kernel. The primary kernel is the first installation of CTask. This kernel installs all basic interrupt handlers, the DOS and keyboard support, and the system tasks (timer, killer). It basi- cally is nothing else than a normal, stand-alone CTask installation. A secondary kernel is installed by a CTask program run "on top" of the primary. This, naturally, is only possible if the primary program has gone resident (TSR), or has spawned another program (for example COMMAND.COM). A secondary kernel automatically de- tects that a primary copy of CTask is already installed, and does not attempt to re-install the interrupt handlers and system tasks. Instead, it uses a pointer to the global variable block in the primary to access all global CTask data. This results in both CTask copies cooperating such that all events, tasks, and other structures, are common to both invocations, and share all global resources. The names of control structures are visible accross the copies, so that a secondary can access control blocks of the primary, and vice versa. There is a separate control structure, the "group control block", for every invocation (or "task group"). This block links all con- trol structures created by tasks inside the group together, so that the system can remove those tasks and events from the system that belong to the secondary, should the secondary terminate without cleaning up properly. The group control block additio- nally contains pointers to data structures and routines that can not be shared (like the memory allocation routines). The group control block is a static structure that is initialised when you call install_tasker. This primary/secondary structure can be completely invisible if you run CTask programs that could also run as standalone CTask applications. But the automatic data sharing also makes it possible to create multi-level programs, which use a resident part to handle hardware interrupts (for example a com port) in the background, and an independently loadable program (which might even be a MS Windows program or driver) to control the resident part. If the controlling (secondary) program does not itself use multitasking features (i.e. create tasks), there is no need for it to include a full-fledged CTask kernel with all the features, and no need to create a task group. But even if it creates tasks, but will never use the full CTask features if Ctask Manual - Version 2.2 - 90-10-12 - Page 101 there is no background kernel, it will not need to include the code for the basic (primary) interrupt handlers and tasks. CTask 2.1 includes several options for cooperating CTask appli- cations to save code in a secondary program. With all these options, the generated program will not be able to use CTask if there is no primary kernel installed. The first option is to use the "stskmain" object created by compiling tskmain.c with SECONDARY defined. With this define, the install_tasker and remove_tasker routines will only reference the second-level group creation routines. All references to the primary task installation routines, which in turn reference the interrupt handlers and system tasks, are eliminated. Install_tasker returns an error code if there is no primary kernel installed, but all other aspects of CTask will work as usual. A task group is created. The second option is to not call install_tasker at all in the secondary. You need not link either tskmain or stskmain. Calling "ctask_resident" will establish the data link. This link enables CTask to work without a task group, such that everything you do in the secondary appears as if it were executed in the primary kernel. This, however, means that you should not create any CTask control structures in the secondary (or at least you should not allow them to be linked into the name chain). If the secondary terminates without removing all control structures and tasks it created, the pointers chained into the primary links will point to some other program loaded later, which may be destroyed if any action causes those pointers to be referenced. You also may not use dynamic allocation in the secondary, since this would try to allocate memory in the primary applications data space. The third option is to use code sharing with the "stskmain" object. Code sharing requires the primary kernel to be compiled with the CODE_SHARING and LOAD_DS configuration options set to TRUE. With Microsoft C, setting those options in tskconf.h is sufficient. With Turbo C, which does not have the "_loadds" keyword, the primary must be compiled in Huge memory model, and the TC_HUGE option must be TRUE. The reason for this is that the routines can now be called from an application with completely different segment setup. If a routine in the primary kernel is called from a secondary, the data segment register will point to the secondary's data segment. The offsets to CTask structures in the primary code will point to some other data in the secondary. So all routines that could be accessed from the outside must set up the data segment register to point to the primary data. Code sharing uses a "stub table" and an "entry table" for a primitive form of run-time linking. The entry table simply contains the addresses of all global routines present in the primary in fixed order. The stub table contains short "stub" routines that access the entry table through the global variable Ctask Manual - Version 2.2 - 90-10-12 - Page 102 pointer, and jump to the address corresponding to the called stub routine. Both tables are generated from one source, "tskstub.asm". You must first decide which routines should be included in the primary, and edit the stub definitions in this file accordingly. The file is then assembled twice. The copy to be included with the primary is assembled with GEN_JTAB defined (this is automatically done by the standard makefile). The stub table copy for the secondary is assembled without this define. Install_tasker returns an error code if there is no primary kernel installed, but all other aspects of CTask will work as usual. The link_ctask routine can be used before calling install_tasker to verify that the primary kernel is installed and has code sharing enabled. A task group is created. The primary kernel will be slightly larger due to the additional code required to load the data segment on function entry, but the secondary will need to link only those CTask routines that are not defined as entry stubs. The fourth option is to use code sharing with no call to install_tasker. This requires nearly zero code in the secondary, but the same restrictions mentioned with the second option apply. There is one restriction on cooperating applications, whether they use code sharing or not: The control structures for both primary and secondary must be identical. This requires that the following configuration options are identical on compilation of both kernels: TSK_DYNAMIC TSK_NAMED EMS NDP HOTKEYS IBM, DOS, GROUPS (must be TRUE for groups to work at all) If you change those options, the sizes of the global structures, and the location of some fields within them, change, making it impossible to share structures. Linking two kernels with different configurations will not work. You may, however, change all other configurations. It is perfectly legal to compile the primary in large model, and the secondary in small (NEAR_CODE set to TRUE), even if you are using code sharing. The secondary does not have to set the CODE_SHARING option, this option is only required in the primary. Ctask Manual - Version 2.2 - 90-10-12 - Page 103 Secondary application link examples (Microsoft C Large model): Option 1: link myprog+stskmain,,,ctaskms+ctsupmsl/NOE Option 2: link myprog,,,ctaskms+ctsupmsl Option 3: link myprog+stskmain+tskstub,,,ctaskms+ctsupmsl/NOE Option 4: link myprog+tskstub,,,ctaskms+ctsupmsl/NOE Note that the "tskstub" object linked with options 3 and 4 is the one assembled without the GEN_JTAB define. It is not the tskstub.obj created by the standard makefile. The /NOE switch is required for the Microsoft linker, since the entry points in stskmain and tskstub duplicate entries in the standard CTask library. TSR, Spawning, and EMS If you are writing a CTask application that should stay resident or spawn DOS, you will be hard pressed to reduce the space required to a minimum. One option to consider is replacing the standard startup code. This code calls a number of routines to setup parameters and the environment copy, and requests a lot of memory, that most likely will never be used by your program. The source for the startup code is included with MS and Turbo C. Another space saver is the included printf replacement. If you don't need the floating point output, tsk_printf and its cousins give you all the capabilities you'll normally need at greatly reduced space (if you need printf at all in your TSR). In general, memory allocation is not needed in a TSR or spawning program, since you can't allocate once you are resident. Ommitting the memory allocation routines saves another chunk of code. The TSK_DYNLOAD define may be set to FALSE to prevent reference to the memory allocator routines from the CTask kernel even when TSK_DYNAMIC is TRUE to support secondary kernels. Again, you may have to change the C startup code to prevent it from calling routines that allocate memory. The final option is putting some of your code and/or data in EMS memory. CTask 2.1 switches EMS on a task basis, and saves the EMS configuration when a task is created. It would thus be possible to move tasks and their local data into an EMS bank (in the 64k LIM 3.2 page frame), and call create_task with the required page configuration activated. Whenever the task is scheduled in, the EMS page will have been switched correctly. The only restriction is that the task control block itself, and all CTask data structures (event control blocks etc.) must be in common memory. All other data, and even the task's stack, may be in EMS (although having stacks in EMS is generally not recommended). This may be hard to do with C programs, but could possibly be achieved with the use of overlay techniques. Ctask Manual - Version 2.2 - 90-10-12 - Page 104 Functions called by Kernel Routines User-defined functions called from the kernel are the task save/restore functions, the functions activated with timers, watches and hotkeys, and the "remove" functions. Some restrictions apply to those functions. For calling functions on a timeout, hotkey, or watch, the following must be noted: - Timeout/watch functions should be as short as possible, since they run at the highest priority. - The stack area is the area of the timer task, which is relatively small. Do not use large automatic variables. - Timeout/watch functions may not use any functions that could cause the timer task to be made waiting. Since version 2.0, timeout/watch functions are called with interrupts enabled. The definition of the timeout/watch/hotkey function is void Taskfunc funcname (tlinkptr elem) The function is called with a pointer to the timer control block. The user parameter passed to the create_xxx routines is accessible through this pointer (elem->user_parm). The data segment is set to the segment address of the timer control block. Hotkey functions are equal to timeout/watch functions, but they are called from inside the keyboard hardware interrupt. The stack is a local interrupt stack, and the function must not use any CTask routines that could cause a task to be made waiting or to be killed. Remove functions may be called at a time when the state of the system is unstable, i.e. during the "emergency exit". To avoid problems, you should not call any DOS functions, and also refrain from using CTask functions. Remove functions should only be used to uninstall interrupt handlers and do similar cleanups. The functions are called with a pointer to the call chain block, and the data segment is set to the segment address of this block. The definition is void Taskfunc funcname (callchainptr chain) Two functions may be set in the TCB that are called whenever the task defining them is scheduled out (the "save" function) or scheduled in (the "restore" function). The main use for those functions is to save and restore static state variables that are shared among tasks. A windowing package, for example, may have Ctask Manual - Version 2.2 - 90-10-12 - Page 105 global variables describing the current window. If you want to output to different windows from different tasks, you may have to save the current state whenever the task changes. A better way than to copy a number of variables would be to make the windowing package "CTask aware", for example by letting it reference those variables through the user pointer in the TCB. This solution, however, may not be feasible with third-party libraries. That's where the save/restore functions come into play. Both functions are defined as void Taskfunc funcname (tcbptr tcb) i.e. they do not return a value, and receive a pointer to the current TCB (the task control block defining the function). The data segment register is set to the segment address of the TCB. The data segment that all those functions are entered with is not necessarily the same segment as the normal data segment of your program. Especially with far data memory models in Microsoft C, the huge model in Turbo C, or dynamically allocated blocks, you can not rely on the data segment having the correct value, unless you make sure that the control block is located in the same segment. To allow you to access global variables from your code, you should either use the _loadds keyword with Microsoft C, or compile the routine in a separate module with all data references defined extern with Turbo C huge model. The safest way is to collect all data the routine should modify in a single structure, and pass the address of this structure as the user pointer/user parameter. If all data you reference is located in the same file as the control block, it is reasonably safe to assume that this data is in the same segment, and thus accessible without special precautions. You may have to take care not to set the "data threshold" with Microsoft C too low, however, since this may cause data items in the same file to be placed in different segments. The same_seg pragma can be used to avoid this. Ctask Manual - Version 2.2 - 90-10-12 - Page 106 Some notes on potential trouble spots Turbo C console output As mentioned in the manual, console output should generally be done only from one task, or be protected with resources. This is especially true for Turbo C (Version 1.5 and later), because the putch function is NOT REENTRANT. Since other console output also uses putch in the end, you have to be extremely careful not to crash your system by entering the putch routine concurrently. You should use the "conout" module provided with CTask to channel console output through a buffer. If you own the Turbo C library source code, you could replace the "_VideoInt" routine in file "crtinit.cas" with an (inline) assembler equivalent that pushes BP on the stack instead of storing it into a static variable. The timer tick EOI To allow CTask to run concurrently with other background programs that might steal the timer tick interrupt, and to enable high priority tasks to override timer ticks, the tick interrupt handler issues an EOI before calling the scheduler. Later, the tick task will (possibly indirectly) call the original BIOS tick handler, which again issues an EOI for an interrupt that is no longer pending. Although this should practically not pose any problems, since no other interrupts could normally be pending at this time, and the EOI is not stored, some experts believe it is theoretically possible for interrupts to be falsely acknowledged. However, according to the INTEL documentation of the 8259 interrupt controller, the additional EOI can not cause any harm. What the EOI does is to reset the highest priority ISR (Interrupt under Service Register) bit in the PIC. According to Intel's specs, it will never dismiss an interrupt that is not being serviced, since only the INTAK sequence will cause the ISR to be set in the first place. If there is an interrupt under service, the scheduler is not invoked, so the timer chain can't issue an EOI whilst in the middle of another interrupt. So I think it's safe to issue multiple EOIs, and I haven't had any adverse effects with INT8_LATE enabled, even while running serial comms with 19200 bps on a networked machine (which should generate a lot of INTs). If you experience problems in special applications anyway (especially if interrupt priorities have been reprogrammed), you may use the IFL_INT8_DIR installation flag. This flag changes the logic in the timer interrupt handler such that the original interrupt is called first, and no additional EOI is issued. You could also replace the timer-chaining logic with a routine that substitutes the BIOS timekeeping (use the BIOS listing as a reference). This, however, would preclude chaining to TSR's that have hooked the timer tick. Ctask Manual - Version 2.2 - 90-10-12 - Page 107 Debugging Debugging CTask programs can be surprising. The debugger can't know about the task structure of your program, and you can easily sit and wonder for hours why the debugger is behaving so strangely until it finally sinks down: the debugger itself can be preempted. The keyboard and timer interrupts are the main culprits. Both can hit during execution of debugger routines, so that data may be different from what you expect it to be. For example, if you are tracing through code that reads or writes a global variable that is also modified by another task, you may find that this variable has a completely different value when you dump it from the value that was just loaded into a register on the last instruction trace. If you are using Periscope, be sure to let Periscope restore the INT 8 and INT 9 entries. This is not exactly pleasant when you're using a foreign keyboard, but it can avoid a lot of trouble. If you're debugging at the application level, those precautions may not be necessary, but if you want to trace into the kernel routines, you must be extremely careful not to trash the debugger. Ctask Manual - Version 2.2 - 90-10-12 - Page 108 Changes from Previous Versions When upgrading from previous versions, you have to recompile all modules that use any CTask functions or data structures. Due to the changes in the control blocks, just re-linking is not sufficient. Changes for CTask 2.1 to 2.2 Version 2.2 mainly is a maintenance release. Several bugs, some of them severe, were introduced into 2.1 by a number of last- minute changes. Most bugs were reported by S. Worthington. Bugs fixed include - The Microsoft C 5.1 and 6.0 compilers generated incorrect code for the va_arg macro used to access the optional user parameter in the create_timer/watch/hotkey routines. The definition of the last parameter before the "..." as "byte" caused MSC to access an incorrect (odd) offset for the parameter. The "rept" parameter for the create_xxx calls has been redefined as "int" to circumvent this. - Enabling the interrupts early in the scheduler could lead to race conditions if a task was made waiting, but then made runable before the scheduler had enqueued it. This could lead to unpredictable behaviour. The fix eliminates the race condition by enqueueing the task into the appropriate queue immediately, instead of waiting for the scheduler to do it. - The keyboard handler installation caused problems with some older BIOSes, since it assumed too easily that an extended keyboard was present. This caused keyboard input to hang on some machines with non-extended keyboard BIOS. The check has now been made more robust. - The hotkey detection logic would cause an immediate schedule if a hotkey match occurred, without checking for other active interrupts. This could lead to problems if the keyboard interrupt had interrupted another, timing critical, interrupt. The interrupt active check has been added. - The "CALL_PASCAL" configuration option did not work. Half of the implementation was missing in the Assembler parts. This has been corrected, with Assembler routines using a slightly different procedure header, and different public/external pseudo-ops. Assembler routines now can be defined with Pascal calling sequence, and the test file "minres.asm" has been updated to use the new definitions. Ctask Manual - Version 2.2 - 90-10-12 - Page 109 - The TC_HUGE option would not work when given in the assembler command line only, without changing the LOAD_DS option. Also, the ctaskh.tc make-file had an incorrect dependency, causing the tskint17 module to be omitted from the assembly. Both errors have been corrected, you can again specify TC_HUGE without editing tskconf.h. The change also eliminates pass dependency warnings with Tasm 2.0. - Some key definitions in "kbd.h" were incorrect, and some were missing. This has been corrected. - The tsk_switch_stack routine used an incorrect DS in several places if the ROM_CODE option was defined TRUE. This has been fixed, the ROM_CODE option now works as expected. - If a task waiting for a memory/port watch or hotkey was made runable by tsk_wake or a similar action, some locations in the next queue element or the queue header could be destroyed. The logic to identify timer elements has been changed to avoid this problem. - Hotkeys, watches, timeout elements, and tickers created by a secondary invocation were not automatically removed on termination. This would lead to crashes is there was no explicit delete_xxx call. The elements are now chained, removal is automatic. - Some routine prototypes were missing in tsk.h, and the add_event_name function was actually defined as add_name. - The interface between the t_read_key and t_wait_key functions and the INT 16 handler in tskkbd.h was using the wrong DS, which would lead to crashes in secondary invocations. (Fixed in 2.1a) - The "ticker" structure was defined differently in tsk.h and tsk.mac. This would cause problems for programs defining tickers in Assembler modules. (Fixed in 2.1b) Other changes: An optional "checking" mode has been implemented. If CHECKING is defined TRUE in tskconf.h, all task and event pointers are checked for validity on entry to task functions and other strategic points. Although some errors can still go undetected, most memory overwrites or uninitialised pointers that would cause a catastrophic crash will now be caught, and the system will stop with an error message before anything vital is destroyed. The checking also includes a task stack check, which is performed on every scheduler entry. The stack of a task is initialized to a defined pattern (0..FF repeated) on a create_task, and the scheduler checks for the pattern to be present in the bottom eight bytes of the current tasks stack. If this pattern was Ctask Manual - Version 2.2 - 90-10-12 - Page 110 overwritten, the system is stopped. This feature can also be used to determine the maximum amount of stack actually used by a task. The tsksnap module will display the number of unused bytes of stack for all tasks if checking is enabled. The CLOCK_MSEC option, which allows all timeouts to be specified in milliseconds rather than timer ticks, has been changed to no longer require floating point support. The routine to convert milliseconds into ticks was provided by Chris Blum, who also supplied some fixes to other modules required to correctly handle the CLOCK_MSEC option. Timeout elements, watches, and hotkeys can now be created without being activated. Separate enable/disable routines are provided to avoid the overhead involved in creating and deleting elements when switching hotkey-sets or watches. If multiple hotkey entries for the same key/flag combination were created, version 2.1 always activated the first entry entered. Version 2.2 will activate hotkeys in a round-robin fashion. The hotkey checking code now uses the keyboard intercept entry in INT 15 if the BIOS supports it. This should increase portability, since the routine no longer needs to access the keyboard hardware ports directly. Version 2.2 Interface Changes New functions: create_timer_elem create_hotkey_elem create_memory_watch_elem create_port_watch_elem These routines are similar to the old-style create_xxx routines, but they do not activate the created element. enable_timer enable_watch enable_hotkey Enable timer/watch/hotkey elements disable timer disable_watch disable_hotkey Disable, i.e. temporarily suspend, timer/watch/hotkey elements. This is different from the delete_xxx calls, which will release dynamically allocated elements. Ctask Manual - Version 2.2 - 90-10-12 - Page 111 Internal changes: The queue handling logic has been slightly changed to allow run- time structure type checking. The queue head is no longer marked by a zero "kind" field, bit 7 (define Q_HEAD) of this field is now set in a queue head instead. This should not interfere with your programs unless you are traversing internal CTask queues yourself (for example in a modified tsksnap module). The structure and handling of timer/watch/hotkey elements has changed. The link kind now identifies the kind of the element itself, a new struckind field specifies the type of the structure "strucp" points to. The element state is no longer needed, the field was eliminated. To allow automatic removal on termination of a secondary invocation, the elements are now chained. Changes for CTask 2.0 to 2.1 Several bugs were fixed. The fixes include - Killing the current task could crash the system if the task had a dynamically allocated TCB and/or stack. A new "killer" task was introduced to free those blocks after scheduling is complete. - Killing a task with a dynamically allocated stack would try to free an invalid pointer. - Timers and watches with the TKIND_WAKE attribute ignored the repeat specification. - Debugging CTask routines in single-step mode would sometimes unexpectedly step into interrupt handlers, because the Trap flag in the flag word on the interrupt stack would be restored inside the stack switch routine, long before exiting the handler. - Timer/watch function calls were supposed to receive the user parameter when called. Actually, the address of the timer/watch control block is, and always was, passed. The documentation has been corrected. - The INT 15 wait/post handler could be overrun by fast disk controllers, resulting in disk timeouts. - When compiling for embedded systems, i.e. with GROUPS, DOS, and IBM disabled, some statements would not compile, since they referenced undefined field names. - The prototype for c_schedule was missing. Ctask Manual - Version 2.2 - 90-10-12 - Page 112 - The resource for INT 10 could be released prematurely if the video routines used recursive calls. The request_cresource is now used to catch this. The routine get_priority now returns the initial, not the current priority. With variable priority enabled, saving and restoring the priority could lead to a tasks priority gradually increasing. The keyboard handler now supports the extended INT 16 functions. The t_read_key, t_wait_key, and t_keyhit routines use the extended functions if available. The timer interrupt now checks the BIOS keyboard buffer, and sets the key_avail flag to wake up tasks waiting for the keyboard. This supports keyboard stuffers putting characters directly into the buffer. The TURBOC and MSC defines caused conflicts with other libraries. They were renamed to TSK_TURBOC and TSK_MSC. Resources, flags, counters, mailboxes, and pipes can now be initialized statically, i.e. at compile time. This eliminates the need to call the create_xxx routine. The only restriction is that such events are not automatically linked into the name chain. A new function, add_event_name, was created for this purpose. Version 2.1 introduces keyboard hotkeys, which are similar to the timer control blocks and the memory/port watches. Keyboard hotkeys are trapped in the keyboard interrupt handler, and can activate tasks or functions, or set flags, whenever a particular key/shift-key combination is hit. Timer control blocks, watchpoints, and keyboard hotkeys can now specify counter decrementing in addition to counter incrementing. A dec_counter function was added to explicitly decrement a counter. Support for EMS and 80x87 numeric coprocessors was added. The EMS support saves and restores the EMS page map state on every task switch to avoid problems with resident utilities, especially EMS- based disk cachers. The 80x87 support saves and restores the state of the coprocessor on a task switch. The scheduler module was revisited, and interrupts are now enabled most of the time. This should help to reduce interrupt latency. In this context, checks for operations which are illegal in interrupt handlers (task wait, kill current task) were added to help diagnosing problems. Previous versions would usually crash silently in those situations. The task switch save/restore functions are now entered with interrupts enabled, and with DS set to the data segment of the active task control block. A replacement printf module was added. This assembler printf replacement is faster than the standard C printf, and is not model dependent. It can also output to the secondary screen in a Ctask Manual - Version 2.2 - 90-10-12 - Page 113 dual-monitor system. This printf is used in the tsksnap module, which is now model independent except for the snapshot() routine, which uses two C runtime routines (flush and fileno). tsksnap also was fixed to work with small model (some pointers had to be explicitly forced to FAR). Some calls to the snapshot dump routines now need different parameters. A debugging mode provides real-time active task display, and on- screen counters for the scheduler, plus counters for timer and keyboard interrupts and internal interrupt stack usage. The precompiled libraries do not provide debugging, you will have to recompile with the DEBUG option in tskdeb.h changed. The attributes for internal and external functions are now #defined, and can thus easily be changed. This should ease porting to other compilers that require different keywords. Also, the attributes can now be defined for near code, allowing all CTask functions to be compiled in small model if desired. Data pointers still have to be far. All calls from Assembler routines have been converted to macro calls, to allow customizing the calling sequence. Several customization options have been added to better support code-sharing and mixed model compilation and assembly. Secondary kernels now can share the CTask code with the primary invocation. A jump-table linking external modules to installed CTask code can be created, so that foreground programs communicating with background CTask TSRs do not have to link in the full CTask kernel code. A new function, "link_ctask", has been added to check for code sharing installed in a primary kernel. Several changes were necessary to allow access to functions and variables local to a group from shared code. The change also allows applications to call CTask functions from a primary kernel without installing their own secondary kernel. The mechanism for removing interrupt handlers upon group/kernel termination was generalized. Previously, only two "remove" routines (for the SIO and printer handlers) could be set. Version 2.1 introduces the "chain_removefunc" and "unchain_removefunc" functions to allow multiple clean-up routines. Some modules were split up, and IFDEF's added to TSKMAIN to allow "secondary-only" programs. This change is intended for programs that communicate with a background copy of CTask, and don't intend to install the Kernel if that background copy does not exist. The make-files create a "secondary" tskmain, "stskmain.obj", which is not included in the library. Linking with this stripped-down TSKMAIN saves 6-7k of program code. A few other modules also were split up, and routines were shuffled around, to avoid linking unreferenced routines. The tsk.h and tsklocal.h files were amended to include the module name defining the routine to make it easier to locate routines. Ctask Manual - Version 2.2 - 90-10-12 - Page 114 Name pointers for tasks and structures may now be NULL. Structures with NULL name pointers are not linked into the name chain. This is useful for applications linking into CTask without creating their own task group. Name parameters are now specified using the #defined macro "TN". This eliminates the need for explicit #if statements on each and every name parameter. This change makes the code a lot more readable. Minor changes, mostly type-casts, were done in several modules to eliminate compiler warnings. The make-files for the support routines were changed to add the model-letter to the filename for both object and library files. This avoids confusion when you use more than one model. The Turbo-Make files for the support routines and the sample applications were updated to allow model modification from the command line. The special ctsuph.tc make-file is no longer needed. Version 2.1 Interface Changes The interface to the global kernel functions has not changed in version 2.1. Note, however, that the v24_remove_func and prt_remove_func entries have been replaced by the new remove chaining, so this will require changes if you used one of those entries to enter your own remove processing. The global variable "ticks_per_sec" was moved to the global variable block. Since this variable is no longer directly accessible, the "ticks_per_sec" function was added. If you were using task save/restore routines, or timer/watch functions, please note the different handling of DS. DS is now set to the data segment of the associated control block, which normally, but not always, is equal to the segment created by the file the block was defined in. See the "Advanced topics" chapter in the manual for more information. For timer/watch/hotkey functions, the parameter passed is a pointer to the timer element, not the user parameter, as erroneously specified in previous versions of the manual. Interrupts are enabled on entry to all functions, including task save/restore functions. The "screensnap" function in the support module "tsksnap.c" was changed. Previously, you had to specify the screen buffer address and dimensions with the call to screensnap. The new version requires initialising the screen driver with a call to tsk_set_regen or tsk_set_dualdis before calling screensnap, which now only accepts a screen length parameter. The function "csnapshot" has been added to output to the screen using standard Ctask Manual - Version 2.2 - 90-10-12 - Page 115 INT 10 calls. The "snapshot" function still takes a FILE * parameter, but should preferably no longer be used to output the snapshot dump to the screen, since it is significantly slower, and requires DOS access. It should only be used to write the dump to a file or a different device. Changes for CTask 1.2 to 2.0 CTask 2.0 unifies the queue concept, and uses doubly-linked lists for all queues, including the task and timer queues. Although the overhead is slightly higher when inserting elements, the overall logic is greatly simplified, and removing elements from arbitrary points in a queue is a snap. To avoid a timing penalty for the new functionality, all low-level queue handling code was implemented in assembler. The new concept allows better support for the yield() operation, and it also allows an improved handling of timeout elements. With the 1.1/1.2 algorithm, it was not completely safe to process the timeout queue with interrupts enabled, and changes to the queue required great care. The new handling of the timeout queue, which is now sorted, and stores the tick difference to the previous element instead of an absolute count, decreases the amount of time spent in the timeout loop. Watch elements, which still require stepping through all queue elements, have been separated from timeouts. While the processing of the queue still has to be done with interrupts disabled, the timeout/watch action now is completely uncritical. The changes to the queue structures required changes in nearly all modules. The main changes were in the tsksub, tsktimer, and tskasm modules, the tskque module was added. Minor corrections were added 89-12-29 to fix a bug in tsk_remove_int17 (file TSKINT17.ASM), and minor typos in the documentation. The documentation was again fixed 90-01-02, and a warning about TASM 1.0 incompatibilities was added to READ.ME. Version 2.0 Interface Changes Version 2.0 introduces some changes in the interface. Since the changes only affect installation and previously unavailable functions, the impact on your programs should be minimal. If you're using a 1.2 pre-release, watch out for the changes in the name search and ticker functions. The affected routines are install_tasker Two new parameters added. Late 1.2 pre-releases implemented but ignored the "flags" parameter, and recommended setting it to zero. This is no longer true. Ctask Manual - Version 2.2 - 90-10-12 - Page 116 ctask_resident New routine to check if CTask is already resident. find_name Name changed from tsk_find_name, values for "kind" parameter changed. find_group_name New routine for 1.1, in 1.2 this was called tsk_find_group_name. Searches names within a group. The "kind" parameter values changed. yield New routine, schedules with minimal priority. Version 1.2 also had this, but using it could lead to task starvation under certain conditions. get_priority set_funcs set_user_ptr get_user_ptr New routines to access fields in the TCB. create_ticker delete_ticker set_ticker get_ticker New routines for a simplistic time counter. Late versions of 1.2 had similar functions with different names, and different parameters. create_timer New optional parameter. create_memory_watch create_port_watch New routines to create memory/port watch entries. Some pre-release versions of 1.2 don't support the last, optional, user pointer parameter. wait_memory wait_port New routines to wait for memory/port changes. delete_watch New routine to delete watch element. Pre-release versions of 1.2 equated this to delete_timer, version 2.0 requires delete_watch to be different. set_counter New routine to set counter to given value. Ctask Manual - Version 2.2 - 90-10-12 - Page 117 v24_flush_transmit New routine in serial handler to flush transmit pipe. prt_flush New routine in printer handler to flush output pipe. timout functions The timeout function now is passed a parameter, and is called with interrupts enabled. assembler interface All entry points now start with the usual underline, since the extended language-specific procedure definitions are used. The "scheduler" entry was renamed to _tsk_scheduler to avoid catastrophic results of typos. internal functions Previous versions defined most internal CTask functions as far. This allowed calling them from outside the CTask kernel (although that was never recommended). The new version no longer allows this, since internal functions are near relative to the common CTask code segment. Changes for CTask 1.1b to 1.2 The never released version 1.2 added the concept of task groups, and the save/restore of internal DOS variables, to support spawning and TSR'ing CTask programs. The TSKDOS module went through several changes in the pre-release copies. All relevant global variables of CTask were grouped into a single structure, and are indirectly accessed through a pointer. This allows linkage between multiple copies of CTask, with automatic detection of other copies. This change required adding new structures, and changing the task control block to accommodate the new group linkage and the space for the DOS variable swap. Also new in 1.2 was the addition of a stack switch on entry to all interrupt handlers. This change was required to eliminate problems with TSR's, especially networks, and to support spawned programs that supply only a minimal amount of stack. CTask now allocates local stacks from a stack pool to hardware and software interrupt handlers. On entry to the scheduler, the task registers are no longer pushed on the stack, but instead are stored in the task control block. This again mandated a change to the TCB. Ctask Manual - Version 2.2 - 90-10-12 - Page 118 Support for memory and port watches that check the state of a memory location or an I/O port on every tick was added. A "ticker" structure that allows simple timeouts in polling tasks was introduced. Task switch save/restore functions were added. The printer output driver was reworked, an an INT 17 interface driver has been added. The INT 15 printer output support was dropped. Resources to protect concurrent access to INT 10 and INT 13 were added in the TSKDOS module. The timer tick interrupt now supports both early and late INT 8 chaining (and the INT9 stuff has finally been renamed to INT8). This change was required to support network software that would time out without really having waited long enough if the INT 8 task was postponed, and ticked a number of ticks at once. It can also avoid incompatibilities with other software that does strange things in the timer interrupt. Installation of the new INT 8 handling is optional. Installation flags now allow on-line customization of some functions, especially the installation of some of the BIOS interrupts, and the INT 8 algorithm. The name-searching functions were augmented to better support searching local to groups, and searching groups. The make-files were cleaned up, and the Turbo C make-files changed to work with Borland's make. Support for the Turbo C Huge model was added, assembler files now load the DS register when necessary. The placement of external definitions in the assembler files was changed to avoid the fixup errors that appeared when assembling with TASM instead of MASM (thanks for H.J. Haug for pointing this out). All CTask routines are now allocated in a common code segment. This allows calling local functions with a near call. All files were polished a bit, with a version number and change date at the top. Comments have again been added. No warnings remain for Turbo and Microsoft with all warnings enabled. All files were affected, and some new files were added. Ctask Manual - Version 2.2 - 90-10-12 - Page 119 Changes for CTask 1.1 to 1.1b Release 1.1b fixed a minor bug in tskmain.c which prevented the main task from being delayed. Thanks to Kent J. Quirk for reporting the bug. Release 1.1a was necessary to fix three severe and some minor bugs in release 1.1. The bugs corrected in 1.1a were - tskasm.asm: Interrupts enabled too early in the scheduler - tskdos.asm: Registers swapped in DOS version test - tsksio.c: Incorrect loop variable in v24_sio_initialise - tskmain.c: Function tsk_dis_preempt missing - tsksnap.c: Incorrect format specification for continuation line - tskasm.asm: Task state incorrect for eligible tasks Also some minor changes to eliminate warnings, and changes to the test files so they no longer use concurrent console output. A console output task was added ("conout.c" and "conout.h") as a sample for channeling console output through a single task. Some changes suggested by Stephen Worthington were incorporated (pipe flush functions, better SIO transmit interrupt handling). Thanks to Peter Heinrich, Stephen Worthington, and Burt Bicksler for reporting the bugs. Changes for CTask 0.1 to 1.1 Thanks to Peter Heinrich, Tron Hvaring, and Dave Goodwin for their suggestions and the bug reports. The main changes, apart from bug fixes, were - Support for named control blocks - Support for dynamic allocation of control blocks and buffers - Task state display support (snapshot dump) - More flexible timer handling, interrupt disable times reduced - SIO support extended for shared IRQ's and on-line definition of ports; save and restore of control registers Ctask Manual - Version 2.2 - 90-10-12 - Page 120 Index add_event_name 58 alloc_resource 96 AT_BIOS 19 BIOS 25 buffer 52 bufferptr 52 byte 36 byteptr 36 CALL_PASCAL 16 chain_removefunc 58 change_timer 68 CHECKING 20 check_buffer 87 check_counter 81 check_flag 79 check_mailbox 83 check_pipe 85 check_resource 77 check_wpipe 85 clear_counter 80 clear_flag 78 clear_flag_wait_set 79 CLOCK_MSEC 18 CLOCK_MSEC 64 code sharing 102 code sharing 103 CODE_SHARING 15 CODE_SHARING 102 console 25 counter 50 counterptr 50 create_buffer 86 create_counter 79 create_flag 77 create_hotkey_elem 72 create_hotkey_entry 74 create_mailbox 82 create_memory_watch 69 create_memory_watch_elem 68 create_pipe 83 create_port_watch 71 create_port_watch_elem 70 create_resource 75 create_task 62 create_ticker 65 create_timer 67 create_timer_elem 67 create_wpipe 83 CRITICAL 61 ctask_active 54 Ctask Manual - Version 2.2 - 90-10-12 - Index 1 ctask_resident 56 ctask_resident 102 curr_task 64 C_ENTER 61 C_LEAVE 61 c_read_buffer 87 c_read_pipe 84 c_read_wpipe 84 c_request_resource 77 c_schedule 60 c_wait_mail 83 c_write_buffer 87 c_write_pipe 85 c_write_wpipe 85 dec_counter 81 DEF_COUNTER 80 DEF_FLAG 78 DEF_MAILBOX 82 DEF_PIPE 84 DEF_RESOURCE 76 DEF_WPIPE 84 DEF_xxx 36 delete_buffer 86 delete_counter 80 delete_flag 78 delete_hotkey 74 delete_mailbox 82 delete_pipe 84 delete_resource 76 delete_ticker 65 delete_timer 68 delete_watch 72 delete_wpipe 84 disable_hotkey 74 disable_timer 68 disable_watch 72 DOS 19 DOS 25 DOS 103 dword 36 EMS 20 EMS 103 EMS_SAVE_SIZE 20 enable_hotkey 74 enable_timer 68 enable_watch 72 entry table 102 farptr 36 FAR_STACK 17 find_group_name 58 find_name 57 flag 50 flagptr 50 Ctask Manual - Version 2.2 - 90-10-12 - Index 2 flush_pipe 85 flush_wpipe 85 funcptr 36 funcptr_dword 36 funcptr_int 36 funcptr_void 36 F_CRIT 48 F_STTEMP 47 F_TEMP 47 F_USES_NDP 48 GEN_JTAB 102 get_priority 63 get_ticker 65 get_user_ptr 64 group control block 101 GROUPS 18 GROUPS 103 group_rec 49 Hotkey functions 105 HOTKEYS 20 HOTKEYS 103 IBM 19 IBM 103 IFL_DISK 55 IFL_INT15 56 IFL_INT8_DIR 55 IFL_NODOSVARS 56 IFL_NOEXITCHECK 56 IFL_PRINTER 56 IFL_VIDEO 55 inc_counter 81 installation flags 55 install_tasker 54 INT8_EARLY 19 INT8_LATE 19 intprocptr 36 kbflag 42 keyboard 25 kill_task 62 link_ctask 57 link_ctask 103 LNULL 35 LOAD_DS 16 LOAD_DS 102 LOCALS_FAR 16 mailbox 51 mailboxptr 51 msgptr 51 msg_header 51 NAMELENGTH 43 nameptr 43 namerec 43 NDP 20 Ctask Manual - Version 2.2 - 90-10-12 - Index 3 NDP 103 NEAR_CODE 16 NEAR_CODE 103 pipe 52 pipeptr 52 pipe_free 85 preempt_off 59 preempt_on 59 primary 101 primary kernel 101 PRI_INT8 19 PRI_STD 18 PRI_TIMER 18 prt_change_control 95 prt_complete 95 prt_flush 95 prt_install 94 prt_remove 94 prt_remove_all 95 prt_status 95 prt_wait_complete 95 prt_write 95 qelem_pri 37 queheadptr 38 queptr 37 queue 38 queue_head 38 read_buffer 87 read_pipe 84 read_wpipe 84 release_resource 76 remove function 105 remove routine 59 remove_tasker 56 request_cresource 77 request_resource 76 resource 51 resourceptr 51 restore function 44 restore function 105 ROM_CODE 17 save function 44 save function 105 schedule 60 sched_int 60 secondary 101 SECONDARY 102 secondary kernel 101 send_mail 82 set_counter 81 set_flag 78 set_funcs 64 set_priority 63 Ctask Manual - Version 2.2 - 90-10-12 - Index 4 set_task_flags 63 set_ticker 65 set_user_ptr 64 SINGLE_DATA 20 spawn 26 start_task 62 stop_task 63 stub table 102 ST_DELAYED 46 ST_ELIGIBLE 46 ST_KILLED 46 ST_RUNNING 46 ST_STOPPED 46 ST_WAITING 46 tcb 46 tcbptr 45 tcb_rec 45 TCMP_CHG 40 TCMP_EQ 40 TCMP_GE 40 TCMP_GES 40 TCMP_LE 40 TCMP_LES 40 TCMP_NE 40 TC_HUGE 16 TC_HUGE 102 TELEM_HOTKEY 40 telem_hotkey 42 TELEM_MEM 39 telem_memwatch 42 TELEM_PORT 39 telem_portwatch 42 telem_timeout 42 TELEM_TIMER 39 TFLAG_BUSY 41 TFLAG_ENQUEUE 41 TFLAG_REMOVE 41 TFLAG_REPEAT 41 TFLAG_TEMP 41 TFLAG_UNQUEUE 41 TFP_OFF 35 TFP_SEG 35 ticker 50 ticker 65 ticks_per_sec 64 tick_ptr 50 TIMEOUT 37 Timeout/watch functions 105 Timeouts 64 TKIND_COUNTDEC 39 TKIND_COUNTER 39 TKIND_FLAG 39 TKIND_PROC 39 Ctask Manual - Version 2.2 - 90-10-12 - Index 5 TKIND_TASK 39 TKIND_WAKE 39 tlink 42 tlinkptr 42 TMK_FP 35 TN 36 tsk_alloc 96 tsk_calloc 96 tsk_cli 61 tsk_disport 99 tsk_dis_int 60 tsk_dis_preempt 59 TSK_DYNAMIC 17 TSK_DYNAMIC 103 TSK_DYNLOAD 17 tsk_ena_int 61 tsk_ena_preempt 59 tsk_fprintf 97 tsk_free 96 tsk_inp 61 TSK_NAMED 18 TSK_NAMED 103 TSK_NAMEPAR 17 TSK_OFFSETOF 35 tsk_outp 61 tsk_printf 97 tsk_putc 97 tsk_puts 98 tsk_realloc 96 tsk_regen 99 tsk_regen_o 99 tsk_regen_s 99 tsk_rprintf 97 tsk_rputc 98 tsk_rputs 98 tsk_scheduler 60 tsk_setpos 99 tsk_set_attr 99 tsk_set_colour 98 tsk_set_currdis 98 tsk_set_dualdis 98 tsk_set_mono 98 tsk_set_regen 99 tsk_sprintf 97 tsk_sti 61 TSK_STRUCTOP 35 tsk_use_ndp 54 tsk_vfprintf 97 tsk_vprintf 97 tsk_vrprintf 97 tsk_vsprintf 97 TSR 26 TTIMEOUT 37 Ctask Manual - Version 2.2 - 90-10-12 - Index 6 TWAKE 37 TWATCH 37 TYP_BUFFER 43 TYP_COUNTER 43 TYP_FLAG 43 TYP_GROUP 43 TYP_HOTKEY 43 TYP_MAILBOX 43 TYP_PIPE 43 TYP_RESOURCE 43 TYP_TCB 43 TYP_TIMER 43 TYP_WATCH 43 TYP_WPIPE 43 t_delay 66 t_keyhit 88 t_read_key 88 t_wait_key 88 unchain_removefunc 59 user pointer 44 v24_change_baud 90 v24_change_dtr 90 v24_change_parity 91 v24_change_rts 90 v24_change_stopbits 91 v24_change_wordlength 91 v24_check 92 v24_complete 93 v24_define_port 88 v24_flush_receive 93 v24_flush_transmit 93 v24_install 89 v24_modem_status 93 v24_overrun 93 v24_protocol 92 v24_receive 92 v24_remove 90 v24_remove_all 90 v24_send 92 v24_wait_complete 93 v24_watch_modem 91 wait_counter_clear 80 wait_counter_set 80 wait_flag_clear 78 wait_flag_set 78 wait_hotkey 74 wait_mail 82 wait_memory 70 wait_pipe_empty 85 wait_port 72 wait_wpipe_empty 85 WAKE 37 wake_task 63 Ctask Manual - Version 2.2 - 90-10-12 - Index 7 WATCH 37 word 36 wordptr 36 wpipe 52 wpipeptr 52 wpipe_free 85 write_buffer 87 write_pipe 85 write_wpipe 85 yield 60 Ctask Manual - Version 2.2 - 90-10-12 - Index 8