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How To Set Up !STem ===================== The text in this file contains useful information about how to configure and use STem. I would advise first time users to read as much of it as possible, since it explains some of the problems that may be encountered, and also the limitations of the emulator. What Is STem ============ STem is an Atari ST emulator for Acorn RISC OS computers. It consists of two separate, but related programs. There is the configuration program which is multi-tasking and runs on the desktop, and there is the emulator which is single-tasking and does not run on the desktop. In fact, the emulator can run without the configuration program, but then the configuration has to be specified as a series of command line options, which is not very user friendly. It is hoped that eventually, the configuration program will be incorporated into the emulator. This will bring a number of benefits, but mainly the possibility that the emulator will become multi-tasking as well. Minimum Requirements ==================== In order to be able to run STem you will need: • A computer with at least an ARM610 processor (StrongARM recommended) • RISC OS version 3.50 or greater • 1 to 5 Mbytes of free memory • 1Mbyte of video ram (optional, but strongly recommended) • A TOS image (see the 'TOS Images' section) • Some disk images (see the 'Disk Images' section) • Shared C Library module (version 3.75 or greater) I cannot understate the importance of using a StrongARM processor when using STem. I'm afraid it really does need a top-end Acorn machine to do the program any justice. Installation ============ Copy the !STem application to a directory on a hard disk (it will probably run from a floppy disk, but this is not recommended). The directory should not be too far from the root directory, due to a limitation of 256 characters for path names. !STem can operate from read-only filing systems, such as locked hard disks, or even CD-ROMS, although you will need to place writable disk images in a different location (see the 'Disk Images' section). Configuring & Running STem ========================== To run STem double click on the !STem application in a filer window. Provided that there is enough free memory (48K is sufficient), and the necessary modules are present, the STem configuration program will load onto the icon bar. Just about everything in this configuration program is able to provide interactive help. To make use of this feature you will need to have a program such as !Help or !BubbleHlp loaded as well. Clicking with the middle mouse button on the STem icon on the icon bar will cause a menu to be opened. The menu has the options 'Info' and 'Quit'. These should be self explanatory, so I won't explain them any further. Incidentally, if you have web access, clicking on the name field in the info window will *hopefully* take you to the STem web site. Clicking with the left mouse button on the STem icon will cause the configuration window to open. The configuration window is split into four parts: The pane at the top allows several groups of settings to be maintained at once. New groups can be added, and old groups deleted using the 'New' and 'Delete' buttons. A minimum of 1, and a maximum of 8 settings groups can exist at any one time. The name of the currently selected group is shown, and can be edited by clicking on it. The name is limited to a maximum of 11 characters. Next to the name is a button, which when clicked on, will display a complete list of all the currently defined settings groups. Choosing an item from the list will cause that group to be displayed. The pane on the left, which lists the various parts of the emulator which can be configured. Selecting one of these options will cause the contents of the pane on the right to change. The pane on the right (as mentioned above) expands on a single topic, and lists either a series of option buttons or a series of radio buttons. Click on a radio or option button to change the configuration for the current settings group. Finally, there are a series of buttons at the bottom of the window. Clicking on the 'Save' button will cause all the currently defined settings groups to be saved (inside the !STem application). The 'Cancel' button will close the configuration window, and the previously saved settings groups will be restored. The 'Start' button will start the emulator using the currently selected settings group. Command Line Options ==================== The emulator can be run from the command line, provided that the !STem application has been seen (i.e. booted) by the filer. Just type 'STem' at the star prompt, proceeded by any of the following command options: -blitter This will enable blitter chip emulation, and by default it is not selected. See the 'Blitter Chip' section for further details. -clock This will enable emulation of the Mega-ST real-time clock, and by default it is not selected. See the 'Real-Time Clock' section for further details. -colour The Atari ST has hardware for detecting the monitor type. This option (which is the default) will cause a colour monitor to be detected. See the 'Graphics Systems' section for further details. -dma This option will enable emulation of the STe dma chip, which allows the playback of sampled sound without using the YM2149 chip (and hence without using very much processor time). By default, dma playback is disabled. Note: STem cannot output any sound yet, so this option is not very useful. -debug This option will enable the production of a text file called '<STem$Dir>.debug' when the emulator is quit. The file contains details about the internal status of the emulator, and I may ask you to send it to me if there is a problem. By default this option is not selected, and you should not normally need to enable it. -ecolour This is the same as '-colour', except that the graphics system will be based on the Atari STe, rather than the Atari ST. See the 'Graphics Systems' section for further details. -emono This is the same as '-mono', except that the graphics system will be based on the Atari STe, rather than the Atari ST. See the 'Graphics Systems' section for further details. -help This will display a help page showing all the command options available, and the current version number of the emulator. The emulator will stop when this option is used. -joysticks This will enable the detection and use of up to 2 joysticks. It is disabled by default. See the 'Joysticks' section for further details. -mc##### This will allow emulation of different processors, but is rather redundant at the moment, as only the Motorola 68000 is fully supported. Some features of the 68010 and 68020 are partially implemented, but it will be some time before they are complete. See the 'Microprocessor' section for further details. -mono The Atari ST has hardware for detecting the monitor type. This option will cause a monochrome monitor to be detected. See the 'Graphics Systems' section for further details. -ram#### See the 'Memory' section for further details. -savescreen Enabling this will cause the screen to be saved as a sprite when the emulator is quit. It is disabled by default. The sprite will be called 'screendump' and the file will be saved as 'screen' in the currently selected directory. The sprite will be the same size as the entire Acorn screen, which may be larger than the Atari screen. The implementation of this feature is likely to change in future. -tos### See the 'TOS Images' section for further details. -ym2149 This will enable the production of sound using the YM2149 sound chip. Sound production is disabled by default. Note: STem cannot output any sound yet, so this option will have no effect. Invalid command line options will produce an error message, and the help page will be displayed. The emulator will then stop. TOS Images ========== The Atari operating system is known as 'TOS', and STem will not run without a copy of it. If you own a real Atari ST you can make a legal copy of it's operating system, using one of the many programs available on the Internet. Alternatively, you can down-load an illegal TOS image, also from the Internet. There are various different versions of TOS available, but not all of them will work with STem. The following table provides a summary of the current situation: Version Size Status DMA Playback Required ========= ====== ================= ======================= 1.00 192K works optional 1.02 192K works optional 1.04 192K works optional 1.06 256K works yes 1.62 256K works yes 2.05 256K sometimes works yes 2.06 256K works optional 4.04 256K doesn't work unknown Any versions not listed here will definitely not work. The size of TOS images must exactly match the value given above, otherwise STem will not load it. Once you have obtained a TOS image, copy the file to a suitable place on your hard disk - the suggested location is inside the 'TOSImages' directory in the !STem application (SHIFT double-click on the !STem application to open it). The filetype is not important, and only read access is required. You will then need to tell STem the location of the TOS image, and this can be done from the configuration program by selecting the 'TOS Image' section. A box will then appear, into which you can type the path. You can also drag the icon from a filer window into the box, to automatically set it's path. Alternatively, the path of the TOS image can be set from the command line by entering the following: *Set STem$TOSImage [path] where [path] is replaced with the location of the TOS image. The directory of the STem application can be referred to by using <STem$Dir>, so a complete example would be: *Set STem$TOSImage <STem$Dir>.TOSImages.TOS100 Note: when using the configuration program, any path set from the command line will be lost when the 'Start' button is clicked on. The table above also shows whether 'DMA Playback' needs to be enabled. TOS versions 1.06, 1.62 and 2.05 *must* have the 'DMA Playback' option enabled, otherwise they will fail during the boot sequence. In all other TOS versions 'DMA Playback' is optional, and can be enabled if a particular piece of software requires it. See the 'DMA Playback' section for further details. Note: there is an unknown problem with TOS 2.05 which means that it hardly ever manages to complete it's boot procedure. For this reason I do not recommend the use of this version of the operating system at the moment. Note: due to certain timing restrictions imposed by the emulator, TOS 2.06 needs a minimum of 2 minutes to boot to the GEM desktop (this is regardless of the speed of the host computer). During the boot procedure the operating system will perform a memory check, as indicated by the words 'Memory Test:' appearing on the screen. Once this message has been displayed you *must* press the SPACE bar on the keyboard to abort the test. After about 120 seconds the GEM desktop should appear. Floppy Disk Images ================== Floppy disk images are just direct copies of Atari/DOS format floppy disks, and provide the most convenient method of loading/saving programs and data in the emulator. You can create floppy disk images using the FDImage application (available from the STem web site). On RISC OS 3.00 or greater, it is possible to access the contents of disk images just like a normal directory, provided that the type of the image file has been set to DOSDisc (&fc8). To map in a floppy disk image using the configuration program, select the 'Disk Images' section, and enter the path and filename of the image file into either of the first two text boxes (these map to drives A and B - see note below). You can avoid typing in the path by dragging the file from a filer window into the appropriate text box. Alternatively, the mapping can be set from the command line, using something like: *Set STem$DriveAImage [path] or *Set STem$DriveBImage [path] where [path] is replaced with the path and filename of the image file. The suggested location for disk images is inside the 'DiskImages' directory, within the STem application (SHIFT double-click on the !STem application to open it). In this case you can use the system variable <STem$Dir> to refer to the STem directory, e.g.: *Set STem$DriveAImage <STem$Dir>.DiskImages.[filename] It is also possible to for STem to access the real floppy disk drive attached to the host computer. To do this you must set the path to 'ADFS::0.$', where the 0 can be replaced with any valid floppy drive number. When using this you MUST ensure that the floppy drive only contains a DOS/Atari format disk. Acorn format disks will not work, and leaving them in the drive could lead to them being corrupted! The emulator cannot detect disk changes, so once it has been started you should not attempt to change the floppy disk, as this could also lead to disk corruption. Note: on the Atari ST, up to 2 floppy drives can be connected, and these always occupy drive letters A and B. Thus you should only attempt to map floppy disks and images onto these drive letters. Even if you only map single disk or image, there will still be two drives A and B available, but they will both refer to the same device. Whatever the source of the drive mapping, STem only permits sector based read and writes to take place. If a program attempts to read/write/format a track the result is undefined. The read/write status of each drive mapping is determined when the emulator is first started, and cannot subsequently be changed. Disk images can be write protected by either changing the image file attributes to read-only, or by placing the image file inside a read-only filing system. Disks can be write-protected in the usual manner, i.e. with the plastic tab. Limitations in the Atari operating system and it's DMA chip mean that only disks with a sector size of 512 bytes can be used. Attempting to use different sized sectors will cause STem to abort with an error. Note: STem cannot detect disk changes, so to prevent possible data loss or corruption you should not attempt to use a different disk once the emulator has started. This applies even if you don't explicitly access the disk, since STem makes itself aware of all disks during it's initialisation phase. Hard Disk Images ================ This feature is not available yet, but once implemented it will allow images of DOS format hard disks to be used just like a normal Atari hard drive. On the Atari ST floppy drives always map to drives A and B. All other drive letters are available for use by other devices, and this includes hard disks. The Microprocessor ================== The Atari ST uses the Motorola 68000 processor. This is a 16/32 bit processor, which has a complex instruction set. Later Atari computers, such as the TT and Falcon, used more advanced members of the 68000 family. STem can fully emulate the 68000 processor, and a limited amount of support is provided for the 68010 and 68020 - these last two processors are still under development, so don't be surprised if they don't work properly. The processor can be selected from the 'Processor' section in the configuration program. Alternatively, the processor can be specified on the command line using '-mc68000', '-mc68010' or '-mc68020'. Memory ====== The Atari ST could cope with a maximum of 4 Megabytes of RAM, although in those days, memory was very expensive, and you were lucky if you had more than ½ Megabyte fitted. STem can emulate an Atari ST with as little as ¼ Megabyte of RAM to it's maximum of 4 Megabytes. Obviously, you must have an appropriate amount of RAM fitted to your computer to make full use of this feature. The size of the RAM can be specified in the 'RAM Size' section of the configuration program. Alternatively, from the command line, the options '-ram256', '-ram512', '-ram1024', '-ram2048' and '-ram4096' can be used to specify the size in Kilobytes. By default, ½ Megabyte of RAM will be used. Cartridge Images ================ The Atari ST had a special port which allowed you to plug in 128Kbyte ROM cartridges. These cartridges were never a great success, and indeed, I have never seen one. However, just incase there are any still in use I have provided an option whereby an image of a cartridge can be loaded into the appropriate address space in the emulator. It is up to you to figure out how to get the cartridge image in the first place, although for anyone with a limited amount of Atari programming experience this shouldn't be too difficult. The image file must be exactly 128Kbytes in length, and the filetype is not irrelevant. You will then need to set a system variable from the command line with the path of the image file: *Set STem$CartImage [path] This must be done from the command line, because this feature has not yet been added to the configuration program. Keyboard Mappings ================= The keyboards of the Atari ST and Acorn are different in both the number of keys present and their positions. This may make it difficult to use some programs, such as games, where the new layout makes it awkward to enter combinations or sequences of key presses. When the emulator is started it tries to ascertain, from the TOS image, the type of keyboard which the original Atari would have had. It will then try to match up the keys of the Acorn keyboard with the appropriate Atari key. Sometimes conflicts occur (especially with the keys "£@#~\| ) which it is impossible to resolve. Some of the possible key mappings are shown below. Which one applies to you depends on what combination of Acorn keyboard and TOS image you have: Acorn (UK Keyboard) Atari (UK TOS) ===================== ===================== F1-F10 F1-F10 F11 undefined NOTE---> F12 stops the emulator ESC ESC TAB TAB `¬¦ `¬ -_=+ -_=+ []{} []{} ;:'@#~ ;:'@#~ ,.<>/? ,.<>/? \| \| A-Z/a-z A-Z/a-z 0-9 0-9 SPACE SPACE RETURN RETURN BACKSPACE BACKSPACE left SHIFT left SHIFT right SHIFT right SHIFT CAPS LOCK CAPS LOCK left & right CTRL CONTROL ALT & ALT GR ALTERNATE NOTE---> PRINT SCRN/SYSRQ stops the emulator SCROLL LOCK undefined NOTE---> PAUSE/BREAK resets the emulator INSERT INSERT DELETE DELETE HOME CLR/HOME END undefined PAGE UP HELP PAGE DOWN UNDO cursor keys cursor keys NUM LOCK (see the 'Joysticks' section) keypad 0-9 keypad 0-9 (only if NUM LOCK is on) keypad /*-+. keypad /*-+. keypad ENTER keypad ENTER undefined keypad () Acorn (UK Keyboard) Atari (Spanish TOS) ===================== ===================== ¬ ~ ` ç ! ¡ (upside-down exclamation mark) " ¿ (upside-down question mark) ^ / [ ' { " ] ` } ^ ' ; @ : # \ ~ | , , < ? . . > ! / undefined ? undefined Pressing 'undefined' keys will not cause anything to happen, but in future they may be used for other purposes. Note that the keys F12 and PRINT SCRN/SYSRQ will stop the emulator, and return to the desktop. The state of any running programs will be lost, so be sure to save anything important first! Also, the PAUSE/BREAK key acts like a reset button on the emulator, and will cause a warm boot to be performed - this means that reset-proof programs will survive, but everything else will be lost. The keyboard repeat rate/delay is controlled by the Atari operating system, and any Acorn configurations will have no effect. You should also note that the CAPS LOCK indicator on the keyboard bears no relation to whether the Atari operating system thinks CAPS LOCK is on or off, although by chance they are sometimes synchronised with each other. The 'Keyboard' draw file in the Documents directory shows the layout of keys on a UK Acorn keyboard when using an English TOS image. The Mouse ========= The Atari ST uses a 2 button mouse to move the pointer around the screen. The 3 button Acorn mouse will work correctly, but the middle button is unused. An alternative method for moving the mouse pointer using the keyboard, is provided by the Atari operating system. This works well in STem, and is often more convenient to use than the mouse: Pressing [ALT] and a cursor key will cause the pointer to move by 8 pixels in the specified direction. To move the pointer by only 1 pixel, rather than 8, press the [SHIFT] key as well. [ALT] + [INSERT] acts as the left mouse button. [ALT] + [HOME] acts as the right mouse button. Various combinations of these can be used to achieve all of the usual mouse manoeuvres, such as dragging etc. Joysticks ========= The Atari ST has hardware to support a maximum of 2 digital joysticks via keyboard ports 0 and 1. The primary joystick is usually connected to port 1, leaving port 0 for the mouse or the optional second joystick. STem can access up to 2 analogue or digital joysticks on the host computer, providing that they are compatible with the Acorn joystick SWIs. The first and second joysticks detected will be mapped onto joystick ports 1 and 0 respectively. The code to handle the joysticks is disabled by default. To re-enable it select the 'Joysticks' option in the 'Other Hardware' section in the configuration window. Alternatively, from the command line, use the option '-joysticks'. When the joysticks option is disabled, you can optionally use the numeric keypad to control the input to port 1 - this may be useful for those people who do not have a joystick. It can be enabled at any time by turning NUM LOCK on the numeric keypad to OFF. When NUM LOCK is off, the keys 0 to 9 will cause the following joystick events to occur: Key Joystick Event === ======================= 1 movement down and left 2 movement down 3 movement down and right 4 movement left 5 fire 6 movement right 7 movement up and left 8 movement up 9 movement up and right When NUM LOCK is on, the numeric keypad will behave normally. The Parallel Port ================= No parallel port emulation is yet provided, but watch this space, as it should be a relatively easy problem to sort out. The Serial Port =============== The Atari ST is equipped with an RS-232 serial port, but due to hardware/software limitations it has a maximum speed of 9600 baud. STem does not yet provide emulation for the serial port, although it is one of the things I am keen to implement. One of the main problems is that programs running on the emulator may not be able to control the flow of data over the serial port as fast as is necessary. This could possibly result in slow and/or unreliable communications. The MIDI Ports ============== On the Atari ST there are two ports for MIDI communications. One is a MIDI IN port, and the other is a strange combination of MIDI OUT/THRU. No provision has been made in STem for these ports, since they are not a standard part of Acorn computers. If anyone wishes to use MIDI programs, and has the necessary interface on the Acorn side, please let me know, and I will try my best to work something out. You would need to supply information about the SWIs to read/write and control the interface, and preferably be willing to do a bit of testing for me. The Blitter Chip ================ The blitter was a custom chip built into some Atari computers for moving/combining large blocks of memory. It's main advantage was that it was very fast, and could work independently, thus freeing up the processor to get on with other tasks. It is used extensively by many programs, especially games, for implementing high speed graphics. Obviously, Acorns do not have such a chip, but STem contains a software version which will provide a suitable level of emulation. The blitter can be enabled by selecting the 'Blitter' option in the 'Other Hardware' section of the configuration window, or using the '-blitter' command line option. The Real-Time Clock =================== Most versions of the Atari ST forgot the time and date when the computer was switched off - a real nuisance. Later versions incorporated a battery backed real-time clock to maintain the time and date when the power was cut. STem provides emulation of this real-time clock, but it is disabled by default. To re-enable it, select the 'Real-time clock' option in the 'Other Hardware' section of the configuration program, or alternatively use '-clock' from the command line. It is only possible to read the time and date from the clock. Programs which attempt to write to the chip, e.g. to alter the date, will fail. Also, not all TOS versions know how to access the clock, because they were written before the clock existed. Graphics Systems ================ The Atari ST has the following graphics capabilities: Mode Resolution Colours V. Freq. ==== ========== =============== ======== 0 320x200 16 (colour) 50/60Hz 1 640x200 4 (colour) 50/60Hz 2 640x400 2 (monochrome) 70Hz All colours can be selected from a palette of 512 colours, with the exception of monochrome mode, where obviously only black and white are available. Some programs require a particular graphics mode to be available. It is up to you to decide which mode each program requires. Usually, programs are able to switch between each of the colour modes automatically, but cannot switch between colour and monochrome (the original computer required a separate monitor for monochrome because of it's different vertical frequency). In order to be able to use any of these modes, you must have a screen resolution on the host computer which is at least as large as that specified above. Where an exact size match is not found, STem will try to use a larger resolution, and the picture will be centred on the screen - this may not be perfect, so you might need to add the modes to your monitor definition file. The vertical frequencies listed above were built-in features of the Atari ST hardware, and could not be modified. STem will always select Acorn modes with the highest vertical frequency, on the assumption that this will provide the most comfortable display. The screen will be updated continuously by STem, at a rate proportional to the number of processor instructions which are emulated per second. The update is also proportional to the number of pixels in the current graphics mode - so higher resolution screens (e.g. mode 2) will take longer to update than lower resolution screens (e.g. mode 0). If a program running on the emulator attempts to change the graphics mode to one where a suitable match is not available on the host computer, then no mode change will occur. However, the program is unlikely to notice this, and will continue regardless, resulting in garbage being displayed on the screen. In the Atari STe (where the 'e' stands for 'enhanced'), the graphics capabilities improved slightly. All graphics modes remain the same as above, except that the colours can be chosen from a palette of 4096, rather than the normal 512. Also, there is greater flexibility over where the screen data is stored in memory. STem only provides a small amount of STe graphics emulation, and this can be enabled by choosing 'STe Monochrome' or 'STe Colour' in the 'Graphics Hardware' section of the configuration window. Alternatively, the options '-emono' and '-ecolour' can be used from the command line. Some programs will only work with ST graphics or STe graphics, but not both - this is a problem with the real computer, not just the emulator. It is up to you to decide which graphics system each program needs. YM2149 Sound Chip ================= The Yamaha 2149 sound chip was a standard part of all Atari STs, so there are a vast number of programs which will work with it. STem provides just enough emulation of this chip to enable most programs to recognise it's presence, and to attempt to use it. However, it is not yet able to playback any sounds. The sound chip also has a number of other important uses, namely in controlling parts of the floppy disk system. These are essential, and as such, have been emulated in their entirety. DMA Playback ============ The YM2149 sound chip was not particularly suitable for playback of high quality samples, so the Atari STe provided an alternative in the form of DMA sound production. STem can only emulate the bare minimum of the DMA playback system - in fact it is just enough to enable the Atari STe operating system to be booted. Programs which attempt to use this hardware may fail, and will certainly not be able to produce any sound. Emulation of the DMA playback hardware can be enabled by selecting 'DMA Playback' in the 'Sound' section of the configuration program. Alternatively, use the '-dma' option from the command line (by default DMA playback is disabled). Note: this option *must* be enabled when using TOS versions 1.06, 1.62 or 2.05. Failure to do so will cause the operating system to crash during the boot sequence. The 'DMA Playback' option has no adverse effects on any other versions of TOS, although there may be certain pieces of software which require it to be enabled. MFP Timers ========== The MFP chip contains a number of timers which are essential for the correct functioning of the operating system. However, for a variety of reasons it is not possible for these timers to 'tick' at the correct rate. Timers A, B and D tick at pre-programmed intervals, according to how many instructions have been executed so far by the emulated processor. The internal settings of these timers are largely ignored. Timer C, however, is of particular importance. It controls the 200Hz system clock, which is used by the OS and many other programs for synchronisation purposes. In distinction to the other timers, this one does take account of it's internal settings, and does attempt to measure the real passing of time. To avoid overwhelming the emulator with interrupts it is necessary to slow down the timer by a factor of 128 - hence instead of 200Hz, it operates at 1.56Hz. The scaling factor for Timer C has a number of side-effects. For instance, benchmark programs which rely on this timer will report exceptionally good performance results - in most cases it is sufficient to divide the results by 128 to get the correct figures. It is also the reason for TOS 2.06 taking so long to boot. I can be contacted at: email: sce196@soton.ac.uk web: http://www.soton.ac.uk/~sce196/stem/ !STem is © Copyright Samuel Ellis, 1998.