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Text File | 1986-02-06 | 52.8 KB | 971 lines

Handling Interrupts using the Macro Assembler! This is the script from the Jerry Stuckle ASM Conference on Interrupts which was held during the regular 8PM Conference on Sunday, 3 February 1985 and refers to the ASM program ASYNCH.ASM in DL4. The script has been slightly edited to conform to the 80 character line. Thanks to Jerry and all who participated to make this a very well organized and informative Conference on Assembly Language. Jerry is constantly on the lookout for suggestions for new topics to cover in future Conferences. Leave Jerry a message or send him Email to his PIN, 72205,234! (30,Jerry S) I think this one is going to run a while! ga (30,Jerry S) Mike --> I'm ready any time, but let's let a few get here first. I do have... introductory text written for each section we will be covering. ga (30,Frank O'D.) Hi! Jerry > Do you intend to cover all of Async, or certain sections? ga (30,Jerry S) Mike -->OK, this is popular, from the number of DOWnloads on the files! ga (30,Jerry S) Frank ->Hi! We'll be going through all of it (if it doesn't get too long). If it (30,STEVE HULL) ?? (30,Jerry S) John --> As long as it's quick, I think we're about ready. ga (30,John Stidd) Is there a good book that explains the file formats of OBJ and LBR? (30,Avi S.) about how long is the CO? Recognize your question Steve. Guess We'll get started. Everyone use ?? for ... Questions O.K.?? ga (30,Jerry S) John --> Nope. That's Microsoft's secret. ga (30,Craig Derouen ) ?? (30,STEVE HULL) HOW CAN I GET THE ENTIRE LINE TO DISPLAY ? Avi <== CO is usually one to one and a half hours. ga (30,Jerry S) Steve --. If you are using an emulator (i.e. VT100),turn it off. ga (30,Julian Thomas ) ?? I have a simple tip for beginning ASM users - ga Question Craig ga (30,Jerry S) Julian -> This CO is for advanced users. Beginning was last week on 129. ga Mike --. We all ready to go? ga Let's hit it, Jerry. How about an Intro? ga (30,Jerry S) OK, all. Just a couple of notes. I will have prepared text before each section of code. At the end of the text, I will ask for questions. Please hold your questions to then, and use the '??' to indicate you have one. If you have a comment which is relative th *THE TOPIC AT HAND*, use '!!' to indicate the comment. Please, let's not get too far off the subject tonight, we have a lot to cover, and not much time to do int in! We will not be looking at specific instructions, rather we will be looking at the code. So, here comes the first introductory prepared text. Good evening all, and welcome to the next in a series of MASM conferences! It has been a long time since we've had one, but I hope we can get them going on a more regular basis. The documentation for tonight is the file ASYNC.ASM on the DL4 database. I hope everyone has DOWnloaded it, we will not have enough time to go over the instructions. Rather, tonight I would like to discuss the use of some simple macros, how to handle hardware and software interrupts, and writing structured code in ASM. Before we get started, there is a bug in the V1.0 assembler which has reared its ugly head (again). This bug is fixed in the V2.0 MASM, so you won't have the problem if you use the V2.0 assembler. The bug is in the LEA instruction, when referencing a FAR procedure. The V1.0 assembler tries to set up a OFFSET:SEGMENT address in the instruction, which is, of course, invalid. To correct the problem you can simply change INT14 PROC FAR to INT14 PROC NEAR Since the entry and exit points to this procedure are via interrupts, it won't make any difference if it is a NEAR or a FAR call. If you DOWnloaded the file after Jan 28, you have a corrected copy of the routine. I will have some prepared text (like this one) on each of several topics in the program. At the end of the text, I will ask for questions. Please limit you questions to the code at hand; we have a lot to cover tonight, and can't stray too far, or we won't get everything in. So, before we get started, are there any questions? ga P.S. please ignore any typos in the text. I don't type so well! ga Fine. Let's get started then. Before we get into the code itself, lets take a look at the program in general. There are some coding conventions I follow which make it easier for me to read Mike, ga and pick up John. ga (30,John Stidd) Would like more info on ASM release 2.0 (30,Jerry S) John, that is available from IBM. You get an updated copy for $75 plus the cover from your old MASM V1.0 manual. Contact your nearest IBM dealer for more info. OK? ga (30,E.J. Tejera ) !! GA E.J. ga (30,E.J. Tejera ) It is not so easy, I tried to exchange V1 and IBM Center here had NO .. knowledge....ga (30,Jerry S) EJ, they should by now. They need to contact their suppliers for more info, if they don't know. ga (30,E.J. Tejera ) I'll keep triyng...ga (30,Julian Thomas ) !! (30,Jerry S) EJ, you do have to send in form. The exchange is not available at the store. ga GA Julian. ga (30,E.J. Tejera ) OK ga (30,Julian Thomas ) Jerry S just said it. Most dealers "should" have the upgrade form... ga (30,Jerry S) OK, any other questions? ga Fine. Let's get started then. Before we get into the code itself, lets take a look at the program in general. There are some coding conventions I follow which make it easier for me to read the output. By no means are they required, and other people have different ideas, but this is the way I do things, anyway, for better or worse. Macros should be placed (or Included) at the start of the file. Normally I will use the IF1/ENDIF around the macros, so they don't print in the final copy. I did not use them here so that you can see the output of the macros. The use of IF1/ENDIF around the macro definitions will not affect the code generation, but will prevent them from being printed. Labels, commands and variables I capitalize. I used to use all upper case letters, but that gets a bit glaring. Also, it helps set off the variable names in an instruction, and I find it easier to read. All lower case seems to get lost in the shuffle. Note that the only times case are important are in the Ifidn and Ifdif psuedo ops. That is, Ifidn <A>,<a> will not compare. Otherwise, case does not matter. Registers I code in upper case. Since all the registers have 2 character Id's, it doesn't glare, and you can spot them easily in the code. A base identifier (i.e. 'H' for Hexadecimal) is in lower case. This way the base doesn't get mixed up with the number. This is especially true when a 'D' can look like a '0' at a quick glance. You will also note I don't place labels on statements. I use the 'Label' psuedo op instead. I find this helpful when writing code. How many times have you had to add a statement after a label, but before the statement the label is on? This way, just insert the line of code. And, it goes without saying that good use of Subttl and Page psuedo ops will make the listing a lot easier to read, and later debugging much faster. It also looks better when showing it to others. I find these general guidelines make the final output look more professional. Again, these are just my ideas, what you want to do may be different. So, are there any questions? ga. Ok, lets take a look at the macros we will be using here. Note that these macros are all general in nature, and came from a macro library I have built up over the years. I have found if you have to execute similiar code more than one place in the program, a macro can be helpful. The first macro is actually a pair - Save and Restore. Save will PUSH the requested regs (up to 10) into the stack. Restore is used without registers, and will pop the regs from the stack. This works because of a not-well documented fact in MASM - if macros are nested, the inner macro can access the paramaters and local variables of the outer macro. The inner macro will not expand when the outer macro is called. The Setint macro is used to set up interrupt vectors. This macro is handy because you don't have to remember the DOS function to use, what registers need to be set, etc. The only restriction here is DS must point to the segment of the vector (preset by DOS for .COM programs.) The Incbuf is used to increment a circular buffer pointer. It is also called from the Putbuf (place a character in the buffer) and Getbuf (get a character from the buffer) routines Bufinit and Flush are used to initialize the buffer and clear the buffer, respectively. All the buffer macros are dependant on the buffer being defined with the BUFFER structure, shown next. This structure defines the size of the circular buffer, and makes room for the data start and end pointers in the buffer. This is a quick overview of the macros. Are there any questions about these macros before we go on? (30,John Stidd) ?? GA John. ga (30,Roy T.) ca << 24 (30,John Stidd) Are the parameters in a Record available even if the Record is never invoked... Initial is nev+sed in the OpCode field in this program. ga correction "never used"(in Op...)ga (30,Jerry S) John, yes they are. This will define the fields. In this case, I am using the Initial record to define some fields. Equates could also be used, but I wnated to show a record. The advantage to using the Record name in an opcode is you can define the record to be any number of bits long; the final length of the variable will be the minimum number of bytes required to hold those bits. ga Any other questions? ga (30,Jerry S) We're moving right along! The next few statements are EQUates for some of the bits we will be using later. An advantage of using EQUates is, if we need to change something later, we only need to change it one place (in the EQU), and reassemble the program. Next we come to the segment header, and initialize our segment to start at 100h. You will notice the first statement is a JMP to Start. This is handy in a .COM program, as you can define the data right at the beginning, where the attributes are known the first pass of the assembler. This can save a lot of problems later with the feared 'Phase error between passes' message. The routine we are JMPing to is at the end. Let's go to label Start. Down here, we initialize the buffer pointers (Bufinit macro), set up the interrupt handlers for INT 0C and INT 14, and execute DOS interrupt 27h. This is the old DOS 1.x terminate but stay resident interrupt. I used INT 27 instead of the newer version in DOS 2.x for compatability reasons - some of the people here may not be using DOS 2.x yet. Note that before we terminate the program, we load the address of RESEND into DX. This is before the routine we are currently executing. This is possible in this case, because this code is executed once (this time), and never again. This is also why we place this code at the end of the routine. While we only save a few bytes here, in programs with larger initialization routines, the savings may be considerable. Now, are there any questions? ga We're doing great, here! Lets move on then. We will skip over the data areas right now, and mention them as we go along. Let's go to the INT 14 procedure. From now on, the updates will be shorter, and we will take the code one procedure at a time. The first proc is INT 14. Note that this is a large procedure, containing several other procedures. The first thing we do coming in is enable interrupts again, save the regs and verify paramaters. If any parm is bad, we return with 0FFh in AL. If the parms are ok, we move the function code to BX, multiply by 2, and call the correct routine to handle the request, via a table (Functbl). The advantage of using a table here is, you don't have to check for each possible function type, and (as in this case), we defined FUNCNT (function count) to be the size of the table/2 (2 bytes per entry). To add a function, copy in your new procedure, and add a pointer to Functbl and you're ready to go. Also, to change the pointer to a routine, just change the Functbl pointer. When we return, we just restore the regs and execute an IRET. The interrupt return is required as we entered the routine via an interrupt. Any questions about this routine? ga (30,Zhahai) ?? GA Zhahai. ga (30,Zhahai) When is the value of an EQU evaluated? ga (30,Jerry S) Hi, Zhahai! The EQU is evaluated whenever the assembler can set it up - that is, if everything is known at pass 1 (like here), it will be set up on pass 1. If something is not known, it may be set up on pass 2. The real value of an equate is to be able to use a meaningful name in an instruction, instead of the value. That is, the statement: Or AH,Timeout is a lot more meaningful then the instruction: Or AH,80h If Timeout is Equated to 80h, the two statements are identical. Just the first one means something, the second may not. OK? ga (30,Julian Thomas ) !! It sin't particularly useful dynamically used! ga (30,Zhahai) A recent thread gave an example wherein an EQU with $... did not evaulate the $ where it was defined (as here), but when... later used. Worried me. I have only used constant EQUs. ga (30,Jerry S) Zhahai, If you look at the output of an EQU, it will have a value associated with it, although it takes up no memory. In your case, the statement: Current_Location Equ $ should set the constant Current_Location to the value in the location counter at this point. If used later, it will point back to where Current_Location was set up. Resend is a good example of that. ga (30,John Stidd) !! Symbol Equ $ doesn't work. Needs Offset $. ga (30,Zhahai) OK, I will ask some more offline. ga (30,Jerry S) No problem... All --. When using the '!!', please wait to be recognized. GA John. ga John, it sure seems to work every place I use it. Note that the location counter is NOT a constant, where 'Offset $' is - that is, there is a difference, (30,John Stidd) ?? and some of the things you do with one cannot be done with another. I would prefer not to get too deep into the difference, but when working with offsets, you should be able to use the 'Equ $'. ga (30,GREG NOLL ) NANOO<NANOO< Is that a question, Greg? ga (30,Jerry S) Mike --. John had a question. ga (30,John Stidd) ?? (30,GREG NOLL ) NO JUST A GREETING I thought you answered John's. If not, GA John. ga (30,John Stidd) I can't remember specifics, but once tore my hair out with a problem... that I finally fixed with Offset $. Is this another 1.00 vs. 2.00 dif? ga (30,Jerry S) John, not really. However, as I said, there are differences. I.E. if you want to find the length of a routine, you may need to use Routine_Length Equ Offset $ - Offset Routine_Start Using: Routine_Length Equ $ - Offset Routine_Start is different, and may cause problems. ga (30,John Stidd) ?? GA John. ga (30,John Stidd) Is there anything published that explains this nitty stuff really well? ga (30,Jerry S) John, the best I can recommend is to hit your nearest large book store. This area is not well documented any place I have found, and most of what I have learned was by trial and error. If you get strange results, look at what the EQU inserted for a value (on the left of the listing). This is the value which will be inserted when the constant is later used. Also, you should be able to see the value in the statement which uses the constant. ga (30,Jerry S) Any other questions? ga Great! Let's continue then. The next procedure, Copen, is used to initialize the port. It sets the speed, parity, number of stop bits, and number of data bits. The only thing here which is a little unusual is the DIVISOR table. We get the speed from the passed request, and convert (via MASK and SHR) to an offset into the DIVISOR table. The value pointed to is picked up and placed into the divisor latch on the Async board, therefore setting thebaud rate. Next we set the Line control register (by the way, we are taking a shortcut and also turning off the DLAB bit, so that we are not using the divisor latch registers any more. Noext we have to save things for a minute and enable the system for interrupts from the async board. This MUST be done before enabling the interrupts at the async board. Otherwise, a pending interrupt from the async board may 'hang' all future interrupts. Note that the STI instruction does not disable the hardware interrupt, just the software processing of the interrupt. After we enable the system for interrupts, we enable the async card. Any time after this, our interrupt routine may get control. We disable interrupts while working with the buffers, and flush both transmit and receive buffers. We get the current status, set the line and modem status bytes, call the status routine (Cstat), and return to caller. This is about the most complex routine in the INT 14 procedure, and I'm sure we have some questions. Ga. (30,DaveA) !! GA DaveA. ga (30,DaveA) Jerry, A typo above. CLI disables interrupts, not STI. ga (30,Jerry S) You're correct, Dave! I saw that this time, but not the other times I proofed it! The code is correct, we have a CLI before and a STI after. ga (30,DaveA) Jerry, just keeping you on your toes (grin). BTW, Wes said to say hi. ga (30,Jerry S) Thanks, Dave. Any other comments/questions? ga (30,Zhahai) ?? GA Zhahai. ga (30,Zhahai) Why the "nop ;allow dummy machine cycle" ? (30,Jerry S) Zhahai, That is to allow any interrupts pending from the async port to be processed. We have to take a machine cycle for the hardware to detect/set up the interrupts. If we have the CLI immediately after inabling interrupts, (30,STEVE HULL) ?? (30,Jerry S) anything pending may or may not be handled right now. This way, anything (30,DaveA) !! (30,Jerry S) pending will be handled immediately by the INT0C routine. ga GA Steve. ga (30,STEVE HULL) Why do you raise RTS during initialization? (30,Jerry S) Steve, in order to send data to the port, we want RTS to come up. The modem should respond with CTS, when it can accept data. Some modems do not care, others may require RTS to be up before data can be sent. Note that this routine assumes full duplex; if you were to write a routine for a half-duplex system, you would not want to bring up RTS immediately. OK? ga (STEVE HULL) thanks GA DaveA. ga (30,DaveA) Jerry, On a Z80, the EI execution is actually delayed for one instruction ... ... time in order to allow a RET to occur, and avoid indefinite nesting. ... ... Is this also true for STI on the 8086? I always use two NOP's just ... ....to be sure. ga (30,Jerry S) Dave, as far as I can tell, the 8088 also can delay the interrupt. One Nop should be sufficient, as the interrupt should occur no later than the end of the next instruction. I this case, it should be handled no later than between the NOP and the CLI. Although 2 NOP's are nice, especially since they are only 1-byte instructions, I have not run into problems using only 1. ga (30,KevinR) !! GA KevinR. ga (30,KevinR) One should note the havoc back to back I/O play on an 80286 chip ... such as in ;Get the status : Again to clear ga. (30,Jerry S) Kevin, that should not cause a problem here. The first status request will pick up any change (delta lines) from the port. The delta lines will be reset by the first request, and the second will only get the lines which were changed after the first request. Otherwise, we might get old status (30,DaveA) !! from a line which changed before the open request was started. This is not really an I/O request, just a read from a port. ga (30,KevinR) !! GA DaveA. ga (30,DaveA) Likewise, don't issue an STI on a 286 for several instruction times after ... ... inhibiting a channel on an 8259. The pipelining on a 286 causes many ... ... new problems. ga GA KevinR. ga (30,Jerry S) Dave, that could be true. I (unfortunately) don't have an 80286. ga (30,KevinR) Jerry, Have you tried running ASYNC.ASM on an IBM AT ?? ..... (30,Jerry S) Kevin, no I haven't, but then I didn't write it for an AT. As I said before, (30,KevinR) The second In opcode is never even seen by the async board ga. (30,Jerry S) this is an example, and not really a ready-to-run routine. It may require modification for your particular system. ga Any other questions? ga (30,John Stidd) |?? GA John. ga (30,John Stidd) In my listing there is a Cli at the beginning, another Cli at end of page... (30,DaveA) !! (30,John Stidd) and no intervening Sti. Is this right? ga (30,Jerry S) True, John. The first CLI should have been removed, it was from an early version. Chalk another one up for Murphy! ga DaveA. ga (30,DaveA) General advice for anyone coding I/O on a 286: Include a jump after every ... ... IN or OUT instruction. this flushes the queue, and provides enough ... ... delay for both the 286 pipelining difficulties, and most external ... ... hardware glitches (like on the AT). ga (30,Jerry S) Dave, good advice, but can we stay with the current routine (on the 8088)? ga (30,DaveA) Yup, sorry. No more on 286, I promise. ga (30,Jerry S) Thanks. Any other questions? ga Well, if you're still with us, we're past the hardest part in the INT14 procedure! The next procedure is the Csend routine. This is fairly simple. First we place a byte from AL into the buffer. Note that, if the buffer is full, the Putbuf macro sets the carry bit on return. If not, the carry bit is cleared. If the buffer is full, we get the status (from Cstat again), make sure the timeout bit is set (indicating buffer full) and return to the caller. If the buffer is not full, we check to see if transmit holding register interrupt is already enabled. If so, we return. If not, the interrupt is enabled, allowing the INT0C routine to pick up the new data and transmit it. As you will see later, the transmit holding register empty interrupt is disabled when there is no more data in the buffer to transmit. Restoring the system interrupt pending is not necessary at this point, and has been deleted from a later version of the program. It actually should have no effect on the program operation, although it is possible that a *very* critical timing condition exists with this code installed. Any questions? Well, let's continue then. The next routine is even easier. The Crcve procedure takes a byte from the receive buffer and returns it in AL. If the buffer is empty, an 0FFh is returned instead. Again, we are using the carry flag to inticate buffer empty. If the buffer is not empty, we return the status (AHSTAT), with the non-error bits turned off. This is for compatability with the existing INT 14 routine in BIOS. Any questions on the Crcve procedure? ga Well, we're getting down to the end of the INT 14 procedure! The next two procedures are going to be talked about together. They are the CSTAT and AHSTAT procedures. Cstat first calls AHstat to set AH with the current status, and then moves the modem status into AL. Ths modem status byte will be set in the INT 0C routine. AHstat is also called by several internal routines. It first gets the line status into AH. It then turns off some bits which relate to the buffer, and gets the buffer status. The Transmit buffer is first. We check two things: Is the transmit buffer not full, and is the buffer not empty; setting the respective bits as necessary. We then check if the receive buffer is empty, and set the receive data ready bit if not. In either case, we return to the caller. The logic depends on the circular buffers: If start of data = end of data, then the buffer is empty. If start of data = end of data + 1, the buffer is full, and nothing more can be inserted into it. Any questions on setting the status bits? Well, I hope everybody's not lost! Let's continue then... OK, the last routine in the INT 14 procedure is Cclos. This routine will disable interrupts from the COM port, then from the system (this must be done after the COM port for the same reasons as above - if the system interrupt is disabled, and the COM port interrupt enabled, interrupts may not get processed later. We also turn off all the modem bits (i.e. Data Terminal Ready, Request to Send, etc.) and flush the transmit and receive buffers. While the last part is not necessary, it cleans up after itself. Any get data request processed after the close will be returned with no data set. Note that a put data will still be processed (if the buffer does not fill up), but the data will never be sent. Any questions about the Clos procedure? Guess not.... OK, we are through with the INT14 procedure. Before we get into the INT0C procedure, are there any questions about what we have covered so far? ga (30,Zhahai) ?? You just make it all look so simple, Jerry. GA Zhahai. ga (30,Zhahai) I'm not clear about the (original) purpose for resetting the... system interrupt in Csend? ga (30,Jerry S) Well, Zhahai, that was to make sure any pending interrupts were handled during developement of the program. I did not have all the routines set up at that time, so I had to make sure any pending interrupts were disabled. That code has been removed (just last week, in another revision). Basically, it was one bit of code which I had in there that didn't get removed when it should have! So much for test code! ga (30,John Stidd) ?? (30,Zhahai) OK ga John. ga (30,John Stidd) Is the most up to date version of ASYNC.ASM now on DL4? ga (30,Jerry S) John, no it isn't. I will be UPLoading a slightly later version this week. I waited as that change was minor, and I didn't want to get too many versions Jerry <== I'll make a note in a bulletin when it is up. O.K. ? ga out there before the CO. Also, I just knew you people would catch something else (like the CLI)! ga And thanks, Mike, I will let you know when it is ready. ga Anything more before Jerry goes on to the next section? ga (30,Jerry S) Now that we're through with the software interface to the routines, let's take a look at the hardware interface. The INT0C procedure should not be called directly by software. It is the hardware's interface to the async board. When the async port requests an interrupt, it is processed by the system. Depending on the state of the interrupt mask bit, an interrupt may be taken now, or held for later processing. It is important that the interrupts be disabled for as short a time as possible (especially at high speeds), or the data coming in may not be handled as quickly as it gets here. Since the transmit is under our control, we can wait (forever, if necessary) for outgoing data, but incoming data must be processed as quickly as possible. When the interrupts are enabled, an interrupt request from the async card will generate an interrupt 0Ch. Our Start routine set up the interrupt to point to this code, where it will be handled. Before we go into the actual code in the INT 0C routine, are there any questions on how the hardware handles the interrupt? ga Let's continue with the software involved, then. The main part of the code re-enables interrupts (disabled when the interrupt was processed by the hardware), saves the registers and tells the system we are available for another interrupt from the COM port. This is done before the current interrupt is handled as the code can handle another interrupt while processing the current one in most cases. We will disable interrupts in the areas which cannot be interrupted. We then look at the Interrupt ID Register to determine what kind of interrupt is to be handled. If the register has the low order bit on (01h), there are no more interrupts to be processed. While this will not occur on the first call (after all, how did we get here?), this is the exit code from a a loop. Also, if a mistake was made and the software calls this routine (by executing an INT 0Ch), it will return with no action performed. If the Interrupt ID register contains other than 01h, an interrupt is pending. These interrupt ID's have the values of 00h, 02h, 04h, and 06h, which works out real nicely for another table. We move the value into BL, clear BH and index into a table from BX to call the appropriate routine to handle the type of interrupt. When thay type of interrupt is handled, we return to here and JMP back to check the Interrupt ID reg again. This is because one interrupt may have multiple functions stacked (i.e. bad parity will set receiver line status and received data available). It is important to handle all interrupt ID's before exiting the routine, or lower priority interrupts will hang. Also notice this is the only backward JMP in the code. These should be avoided if at all possible, as they can cause hard-to-find loops. We could have gotten around it, but I didn't for clarity sake. Now, any questions on the INT0C routine? ga (30,Zhahai) ?? GA Zhahai. ga (30,Zhahai) How well defined is the prioritizing of the Int ID register... Like, what if a recieve comes in while in the loop. ga (30,Jerry S) Zhahai, the hardware is VERY well defined. If an interrupt comes in while processing a higher-priority interrupt, it will be held. If it comes in while processing a lower-priority interrupt, it will be handled immediately. The priority is : Receiver line status (highest) Receive data available Transmit holding reg empty Modem status (lowest). Most of the time, this would come into play as receive data available while setting up to transmit a character. In this case, we have already reset the transmit interrupt (we read the Interrupt ID reg), and the character is being set up to be sent. The receive data can come in at this time. Note also that at speeds below about 48k baud, we should be in and out of our receive routine before the next character comes in. The only delay would be a timer interrupt, which has been accounted for in the calculations of max speed. ga (30,Zhahai) Thanks ga (30,Jerry S) Any other questions? ga Good. Now the next routine is pretty short, and so will be the description. The lowest priority interrupt type is the modem status. Note that the priority of various types is determined by hardware, and cannot be changed. To reset a modem status interrupt, all we have to do is read the modem status register. We go out and get the port, then place the value found into the Mstatus byte so the INT14 routine has the last value in the port. This also minimizes the need for the INT14 routine to access the chip directly. Any questions? ga ?? GA Mike. ga <grin> With the Modem status being the lowest... (30,KevinR) ?? interrupt vector, would it be possible to get the status out of synch? ga (30,Jerry S) Theoretically, but not pratically, Mike. The modem status would come into play when something like carrier dropping, etc. So, for the hardware it should not - the interrupt would be handled before a return to whatever was running.... As for the software, it is possible. The modem status byte reflects the current value, where the receive and transmit buffers may reflect up to 256 characters earlier. So, yes it is possible. However, it is very complex to keep all the buffers in sync (you almost need another buffer to keep the modem status, for instance), which is beyond what I wanted to do here. ga KevinR. ga (30,KevinR) You justed asked it Thanks! ga. (30,Jerry S) Good, two at once! Any other questions? ga The next higher level request is the transmit holding register empty interrupt. (30,Zhahai) !! (30,Jerry S) This means that a byte has been transferred from the holding reg to the shift reg for transmission. The chip now has room for the next character. Note that the chip holds two bytes for transmit at one time - the one being transmitted, and the next one to be transmitted. When we receive this interrupt, we get a byte from the transmit buffer. If a byte is available, we place it into the transmit holding reg and return. If not, we disable the transmit holding register interrupt, as we have nothing more to send at this time. In either case, we return to the caller for processing of any further requests. Any questions? ga Zhahai. ga (30,Zhahai) Just a comment. Ints from this can be stacked 4 deep, no, ga (30,Jerry S) True, Zhahai. But I want to make one thing clear here - interrupts from the system are not the same as interrupt ID's from the port. If, for instance, you receive a character with bad parity, two levels will be set - the Receiver Line Status (for the parity check) and the Receive Data Ready (for the character). If, at this time, the transmit holding register also goes empty, and you lose the carrier, you will have 4 levels of interrupts on the async card, but it will generate only 1 int 0C to the system. All levels must be processed, or a lower-level interrupt will not trip the INT 0C again. ga (30,Zhahai) ?? GA Zhahai. ga (30,Zhahai) How do we keep a critical window from happening after the last... 8250 Int ID was serviced and the return from int? ga (30,Jerry S) Well, Zhahai, that takes a little careful programming. For the most part, you could get by without the STI instruction at entry. Then the IRET will reset the interrupt flag. However, in this case, the code is (almost) entirely quasi-reentrant: that is, it can (in most places) be interrupted while processing. In cases like this it is important to use the stack and registers for saving values, instead of a location in memory which may be changed by another interrupt being processed before this one completes. Also, be thankful for the stack - try an assembler language (like IBM 370 for big systems) which doesn't have a stack. It makes re-entrancy very interesting! ga (30,Zhahai) Understand. But what would the scenario wherein "a lower level int... (30,KevinR) ?? (30,Zhahai) would never trip the 0c int again" ? ga (30,Jerry S) That is why we need to process all pending interrupts. For instance, if we just processed the first one, if a character came in with bad parity the line status and receive data available would be set. The first one we look at would be the receive line status. After that is reset, the Interrupt ID reg will indicate the next (receive data available) is to be processed. If we don't handle it at this time, the receive line status, transmit holding ready and modem status interrupt ID's will not generate an INT 0C, since a higher (or equal) level is waiting to be processed. ga KevinR. ga (30,KevinR) Jerry, will the int0c rtn ever run for more than one char??? ga. (30,Jerry S) Nope, Kevin, as the async port is a character device. You will receive or send one character at a time, and the hardware has no way to handle a second (or third...) character. Remember, we are working with a straight character device, so everything is handled one character at a time. ga Any other questions? ga Let's look at the next routine then. This is the next to highest interrupt type, receive data available. We get the character from the port and place it in the receive buffer. If the buffer is full, the character is not placed in the buffer. Rather, the receiver overrun bit is set in the line status byte, so the next time the program looks at the status, it will find out data has been lost. Any questions? ga Now for the last procedure in our program. The Rcvrlst routine handles the highest priority interrupt type, the Receiver Line Status. This usually indicates an error (i.e. parity check, overrun, etc.) has occurred. Like the modem status, all we are going to do here is take the byte and place it in the line status byte, Lstatus. After this, we return to the caller. Any questions? ga (30,Zhahai) ?? GA Zhahai. ga (30,Zhahai) (sorry to be so inquisitive) Won't this overwrite the rcv overflow? ga (30,Jerry S) That's true, Zhahai. That is something else I want to change in a later release of the code. The most common error would be to get a parity check. The routine is quick enough that the overrun here should not be set. The next version will do two things: Not overlay the overrun bit, and if the character comes in with bad parity (only possible for 5-7 bit transfers), the high-order bit will be set when we receive the character. This way, the program will know which character has bad parity, not just that it occurred. ga Any other questions? ga And Zhahai, don't worry - we're having the CO just to get questions asked! ga Let's continue then.... Now that we're all done with the INT0C routine, are there any questions on the operation of this routine? ga Well, we're finally done! As mentioned in the doc, this is by no means a complete routine. There are many things which can be improved upon. I did not go any deeper, as it is fairly complex as it is, and I felt no need to make it even more so. Rather this routine should be considered a 'learning' program, and can be used as a base for other interrupt drivers for the async port. I hope you all enjoyed the CO as much as I did. I am soliciting ideas for future CO's on advanced programming in assembler language. One of the requests we have had is for Device Drivers. This is a good possiblilty for a future CO. We are also looking for other ideas, though, and all are appreciated. Also please note there are Conferences on the IBM Novice Forum (PCS-129) for beginning assembler language. Watch for bulletins on both SIG's for future CO's. Thanks again, and see you soon! (30,STEVE HULL) !! (30,Jerry S) P.S. Look for a bulletin on the new version later this week. I will also (30,David Watson ) Hear, hear for the Device Drivers CO!! (30,Avi S.) Mike--> can I ask u a question? Jerry, I would like to thank you for everyone. and hope that we get some... (30,Jerry S) have updated the DOC file with the changes that are made. ga More comments for future topics. ... Steve. ga with your question. ga Avi <== Hold just a few more minutes. ga (30,Avi S.) ok (30,STEVE HULL) can you comment in general on some of the more advanced SIO's ? Jerry? Comment on Steve's question? ga (30,Jerry S) Steve, can you give me a better idea of what you're looking for?... I can comment on a lot, most of it not too interesting! <grin> ga (30,STEVE HULL) I'm working with an 8530 and need some help with initializing the sucker!! (30,Jerry S) Steve, I'll byte. which is the 8530? (I don't know numbers, just functions). ga (30,STEVE HULL) if youi have any experience with DMA, I'd be interested. ga Steve <== Why an 8530? ga (30,STEVE HULL) The 8530 is a zilog chip capable of handleing NRZI (30,Zhahai) Thanks, Jerry and Mike. This has been very useful ! ga Jerry <== Want to open up for free-for-all (Read Between the Lines)??? ga (30,STEVE HULL) encoding for SNA. ga (30,Jerry S) Glad you liked it, Zhahai! ga OK, all, let's throw this wide open. The formal part of the Co is over, thanks a lot for you interest and *very* good questions! You also pointed out some of the code I messed up, and as I said, I hope to have a later version in the DL4 lib later this week (oh, my poor CIS bill!). Thanks again, and have a good eveing! ga (30,Zhahai) Jerry <= there is a small flaw in the documentation, point #5... Let me chime in that Jerry needs topics for future CO's. *HIT* hit now!!! ga (30,Jerry S) Steve, I haven't worked with SNA yet. The DMA subject can be touchy, though. (30,Zhahai) Jerry, under changes from ROM int14, bit 1. ga (30,Jerry S) I have done some DMA with the disk adapter, with a fair amount of success, but mostly end up overlaying something and hitting the 'big red switch'! (30,Zhahai) Jerry, Mike, I would love a DMA conf. ga (30,Jerry S) The SNA controller can do DMA, what I would suggest is getting a data sheet ont he chip from one of the manufacturers. ga Jerry, Know anyone comfortable with DMA?? ga (30,Jerry S) Zhahai --> OK, I'll look at it... I don't have a copy of the DOC handy, but (30,STEVE HULL) I'll second the request for a DMA co. gaa (30,Jerry S) I have made a note of it. ga (30,Zhahai) Jerry - just change 'transmit overrun' to 'recieve overrun'. ga (30,Jerry S) Mike, not really any more than I am. I'll check around and see if some of my friends who work with SNA know a little more. Being at a plant site with Jerry <== I wasn't meaning you couldn't handle it, you just sounded shy! ga (30,Jerry S) people working on the PC is a help! ga Mike, I really don't feel comfortable enough to do it, quite frankly... If I had my hands on the chip, I would feel a lot better! I know the theory,.. and had some pratical experience, but not enough for a CO! ga (30,Zhahai) How about disk DMA COnf? ga (30,Jerry S) Zhahai, thanks a lot. Looks like my transmitter doesn't know what... Zhahai --> my receiver is doing! ga Jerry <== Anyone there interested in expanding their capabilities? ga (30,STEVE HULL) yes (30,Jerry S) Zhahai, I don't think we really need one on that; BIOS does it so well! ga Steve <== We'll work on your DMA problem and see what we can drum up! ga (30,Zhahai) Jerry - I fantasize about an asynchronous disk read/write, sets flag when... (30,Jerry S) Steve, want to expand your capabilities? You should hold a CO! Nothing like (30,Jerry S) holding your own to learn the subject! ga (30,Zhahai) Jerry <- done, rather than waiting like BIOS does. ga (30,David Watson ) Mike ==< Thanx (30,Jerry S) Zhahai, I agree. But most programs need to wait for the data anyway, (30,Rick K.) Whats new and exciting tonite? ga (30,Jerry S) Zhahai --. so the time savings would not be too great. ga (30,Zhahai) Mike <- glad you are back and presumabley better. ga (30,Jerry S) Zhahai --> Also, DOS isn't made to handle the interrupts asynchronously, ... Zhahai --> although I've dreamed about it, too! ga Rick <== Just finished Jerry's CO on ASM INT 14 ASYNCH program in DL4. ga (30,Zhahai) Jerry -> It could help a lot for a "type" style program, which otherwise... (30,Jerry S) Good evening, Rick! ga (30,Edward Huang ) DL4 (30,Jerry S) Mike-->I'm surprised how well this went! Some good questions, which indicates... Zhahai <== Just holding on to the edges. Can hardly wait for bedtime! ga (30,Zhahai) Jerry -> has to "lurch" now and then while it awaits disk i/o. ga (30,Jerry S) Mike --> the people kept up, and over at an early time. Last weeks on the... mike --> Novice Forum lasted until almost midnight EST! ga Jerry, You aren't disappointedare you? <grin> ga (30,David Watson ) {_}iMike, I have 2 questions for you? (30,Avi S.) mike-> I do Ave <== You've been waiting all evening! You first and then David. O.K. ? ga I mean Avi (Sorry!) ga (30,Jerry S) Zhahai --> I agree, but then who would rewrite DOS? Otherwise we'd have Zhahai --> kinds of problems! ga Speaking of DOS... JERRY ... When is 3.1??? ga (30,Avi S.) Before I installed my hard disk UI removed the B floppy... (30,STEVE HULL) Thanks for taking the time to put the conference together. See you! (30,Jerry S) Mike --> Don't hit ^B in the CO! ga (30,Zhahai) Jerry <- sigh, too true. I was considering NOT calling DOS during such... (30,Avi S.) but I just left the cable hanging from the floppy controller Good Night, Steve. Have a *GREAT* Week!!! ga (30,Jerry S) Mike, DOS 3.1 should be ready shortly, from the announcement. I'm more Mike --. waiting for my copy of TOPVIEW though. ga (30,Zhahai) Jerry <- I/O, and just unravaeling the FAT myself. (fantasy, remember) ga (30,Avi S.) could this be a cause for the computer not to recognize the hard disk? (30,Jerry S) No problem, Steve, and thanks for coming! ga (30,Jerry S) Zhahai --> I know, I know..... I might recommend you look at the BIOS listing Zhahai --> the disk interrupts. You'll find the loop there, and should be Avi <== Did you reset the System board switches? Who's HD and driver??? ga (30,Jerry S) able to get the DMA you need. ga Mike --. If you don't mind my asking, what were you in the hospital for? ... (30,Zhahai) Jerry -> well, someday. I would almost get a copy of WINDRIVE from... (30,Jerry S) Mike --> nothing serious, I hope (we NEED you!) ga (30,Avi S.) Mike-> its Everex and they claim its not necessary to change any swithches Jerry <== Gastroenteritis that ended up with a tear in the stomach lining!!! (30,Avi S.) but Itried changing them but it still did not help ga (30,Zhahai) Jerry -> from TallTree just for the driver source (Installable). ga Avi <== Did you create the CONFIG.SYS file and have it on your BOOT disk? ga (30,Jerry S) Mike --. Ooo, I'll bet that hurt! I hope you feel better now, though! ga (30,Avi S.) what has to be in the config.sys? (30,Jerry S) Zhahai --. Just do what I do - use a virtual disk. Saves gobs of time,... (30,Jerry S) Zhahai --> and is completely compatable! ga (30,Avi S.) they didn't say anything about it. ga Jerry <== Everything is coming out better now!!! <grin> ga (30,Jerry S) Mike --> I wouldn't complain it it were! ga P.S. <grin> ga (30,mitch jones ) Hello (30,Jerry S) Hi, Mitch! ga (30,Zhahai) Jerry - that was another thought. Could pseudo-DMA, no ints or anything. ga (30,Avi S.) mike-> but they didnt give me a device driver (30,Jerry S) Zhahai --> If you've never used a virtual disk, you're in for a treat! I... Zhahai --> run 320K right now, with occasional 400K as necessary. ga (30,mitch jones ) Thanks, just dropped in to see what's up ga (30,Jerry S) Avi --> When you took out the 'B' drive, did you reset the switches for one... (30,Zhahai) Jerry -> see my disk timing msg, recent. Can copy 1MB from HD to NUL in 9 sec. Jerry <== Anytime, It's a *REAL* pleasure having you here!!! ga (30,Avi S.) They said it wasn't necessary but I tried and it didn't help Avi <== I think you'd better check with your dealer. I don't know of any... (30,Jerry S) Avi --> drive? And is your disk compatable with the IBM XT disk? ga (30,Zhahai) Jerry ->, how much would a ramdisk help? HD is usually fast enuff. ga Avi <== hard disk installation other than for DOS 2.0 and 2.1 and the XT ... (30,Jerry S) Zhahai --> About the same as copying from hard disk... Avi <== that does not require a device driver! GA (30,Jerry S) Zhahai --> For instance, BASICA comes up when you hit the return key, almost... (30,Avi S.) jerry->yes.Its Everex (30,Jerry S) Zhahai --> no delay at all! (If you blink, you miss it!) ga (30,Jerry S) Avi --> I don't have much experience with Everex, but if it is supposed to be... (30,Zhahai) Jerry, Yep, HD is similar. Only reason I see for RamDisk is to save... Zhahai <== My bernoulli drives are almost that fast too!!! ga (30,Jerry S) Avi --> completely compatable, you should be able to format it from the... Avi --> the FDISK program. ga (30,Zhahai) Jerry, wear'n'tear. Or to have a special driver ga (30,Zhahai) Mike -> are they back from the hospital too? ga Zhahai <== I just installed JRAM2 on my PC and can have up to 16 MB RAM disk... (30,Jerry S) Zhahai --> Well, I haven't played with an AT yet (dream), but the Xt... (30,Avi S.) Jerry-> I cant even get it to spin much less format it Zhahai <== If I wanted to install all 8 boards!!! ga (30,Jerry S) Zhahai --> is still noticeably slower. ga Zhahai <== The bernoulli's are on the way. I expect Monday or Tuesday!!! ga (30,Jerry S) Avi --> Hmmm Looks like you have a basic hardware problem there. I (30,Zhahai) Mike, would you use UNenhanced AT + Bernoullis? ga (30,Jerry S) Avi --> would suggest you check the voltages coming into the disk. ga Avi <== Have you addressed drives B, C, D, and on to see if DOS put it ... (30,David Watson ) ~r/ust (30,Jerry S) Mike --. Anything interesting new on the DL files? ga (30,Zhahai) Jerry, I have external Pegasus 23 M, faster than XT disk (what isn't). ga Avi <== some place out in left field? Avi <== That can happen based on switch settings. ga (30,Avi S.) jerry->well what I said is not quite correct... Jerry <== IBM UGE disk for January. I have FileExpress V. 3.0 ready but... (30,Avi S.) the green ready light comes on but I cant get the the red one to come on Jerry <== not up on the SIG yet (drat!!!). ga (30,Jerry S) Mike --. Anything new on the DL databases of interest? ga (30,Avi S.) mik3-> yes I tried all the way up to z! (30,Jerry S) Mike --> What's FileExpress? ga (30,Zhahai) Mike - I started a modified UGE disk, consisting of just the technical... (30,Jerry S) Avi --. Hmmm does the disk spin at all? ga Avi <== Sounds like a trip back to the dealer is the only cure!!! ga (30,mitch jones ) can I jump in with a software question ga Jerry <== Did you get my (drat!!!) ga (30,Zhahai) Mike- extracts, same menu program. Do you think anyone else would like... GA mitch!!! ga (30,Jerry S) Go ahead, Mitch. This is the 'free for all' ga! (30,Jerry S) Got it, Mike... Didn't know if you had gotten mine! ga (30,mitch jones ) Anybody there use Word Star/... (30,Avi S.) jerry->for a split second on cold start (30,Zhahai) Mike - such a thing? I hate to download all the chaff. ga (30,Avi S.) ga (30,mitch jones ) I have a set up problem ga (30,Jerry S) Mike --> Where is the UGE disk? ga (30,Jerry S) What's wrong, Mike? ga (30,Jerry S) OOOps, Make that MITCH! ga Zhahai <== The offer stands for anyone to send a disk in the mail Zhahai <== if they want! ga (30,mitch jones ) I can't get it to install... (30,mitch jones ) into my PC but it works... Jerry <== The UGE disks are in DL0. ga (30,mitch jones ) fine on the office XT ga (30,Jerry S) Avi --. Perhaps you are overloading the power supply, and one of the voltages is going away (although I thought the whole thing would go) ga Thanks, Mike. ga (30,Zhahai) Well, later folks... 's been fun. ga o-o (30,CHARLES ANDERSON ) Hello there ga (30,Avi S.) I guess I'll have to go back to the store mitch <== do you have the WINSTALL program with the WordStar? ga (30,Jerry S) Mitch --. What do you get for messages? ga (30,mitch jones ) Mike, yes... Good night Zhahai. Be 'seein' you later... Mike(30,Jerry S) Hi, Charles! ga (30,mitch jones ) but when I use it... Hi, Charles. Help you with anything? ga (30,Jerry S) 'Night, Zhahai, and thanks again for all your good questions! ga (30,mitch jones ) on the PC set up it wont make a Dir ga (30,CHARLES ANDERSON ) Hi gerry - was someone having voltage problems? ga Avi <== Sorry we couldn't get past the hardware problem!!! ga (30,Jerry S) Charles --. Don't know, almost soundsl like Avi might. ga (30,mitch jones ) Jerry, Error E44 ga (30,Jerry S) Avi --> I suspect something in the hardware. The disk should spin when... (30,CHARLES ANDERSON ) I missed eearlier - but had some which I solved ga (30,Jerry S) Avi --. power is applied. ga (30,David Watson ) {Mike, can you point me to a CO etiquette manual?? ga (30,Jerry S) Mitch --. Hmmm that doesn't ring a bell, and I don't have mu... (30,Jerry S) mitch --> doc handy... What is an E44? ga (30,mitch jones ) Jerry s I don't know... Mitch <== What do you have the default drive set to? C: ??? ga (30,Avi S.) jerry-. it does sound like it's on when I power up and as I said the green... ready light is on but when I try to access it the computer hangs and then... gives the disk not ready error. ga (30,CHARLES ANDERSON ) Avi do I gather you're having some hard disk problems? ga (30,mitch jones ) Mike, no protocol ga (30,Avi S.) It's as if it's looking at the end of the cable of the floppy controller... (30,Avi S.) and not finding anything there. ga Mitch <== No I mean maybe the WS program is trying to access drive C: which... (30,Avi S.) charles-> yup Mitch <== may not be available on your PC? ga (30,CHARLES ANDERSON ) I've had a Davong for two years and been ... (30,mitch jones ) Mike I don't think so... (30,CHARLES ANDERSON ) through a lot - anything I can help on? ga (30,Jerry S) Avi --. Well, if you get a 'disk not ready', the system knows it's there... (30,mitch jones ) to install on the PC and that... (30,mitch jones ) was set to PC. ga Well everyone, since my Doctor doe not know I'm up doing this and I'm ... (30,Avi S.) jerry->I'm not sure if that was the exact error Supposed to be in bed for the next seven days, Guess I'd better head out... (30,Jerry S) Avi --> So your problem seems to be in the access. If you can't format it with Fdisk, you need to take it back to your dealer. ga Anything only the SysOp can answer or take care of??? ga (30,mitch jones ) Mike go to bed and rest ga (30,Avi S.) even just a dir just makes it hang ga Thanks, mitch. See you next week. ga (30,Jerry S) Mike, although it will be hard, I think we can make it by... (30,David Watson ) {Mike, best wishes, get healthy!! ga Jerry <grinning> Thanks to you again!!! ga (30,Jerry S) Mike --> Go to bed, get plenty of rest, and we'll see you next week! ga My pleasure, Mike. 'Night! ga Thanks David and everyone else. Good night and have a good week!!! Bye