CP/M-65

What?

This is a native port of Digital Research's seminal 1977 operating system CP/M to the 6502. So far it runs on:

• The BBC Micro family, including Master, Tube, and Electron; TPA ranges from 14kB on the Electron to 57kB on the Tube.

• Commodore 64; TPA is 46kB.

• Commodore VIC-20; TPA is 24kB.

• Commodore PET 4032, 8032 and 8096; the TPA ranges from 25kB to 57kB on the 8096.

• Commander X16; TPA is 46kB.

• Apple IIe; TPA is 46kB.

• Atari 400/800 XL/XE; 16kB minimum; TPA ranging from 8.5kB up to over 49kB on a 64kB XL/XE machine.

• Oric 1 and Oric Atmos (but not, currently, the Telestrat) with Microdisc interface; TPA 44kB.

• Sorbus homebrew 6502-based computer.

• Olimex' neo6502 6502-based computer.

• nano6502 6502-based SoC for the Tang Nano 20K FPGA board; TPA is 55kB.

• KIM-1 with K-1013 FDC, directly connected SD card module or 1541 drive.

Unlike the original, it supports relocatable binaries, so allowing unmodified binaries to run on any system: this is necessary as 6502 systems tend to be much less standardised than 8080 and Z80 systems. (The systems above all load programs at different base addresses.)

Currently you can cross-assemble programs from a PC, as well as a working C toolchain with llvm-mos. For native development, there's a basic assembler, a couple of editors, a BASIC, and a byte-compiled Pascal subset and interpreter. You need about 20kB to run the assembler at all, and of course more memory the bigger the program.

No, it won't let you run 8080 programs on the 6502!

Why?

Why not?

Where?

It's open source on GitHub!

How?

You have two options:

• Download a binary release. You can then copy this onto a disk for booting on a real machine, or use it in an emulator.

• or build it yourself.

To build it, you will need the llvm-mos toolchain. CP/M-65 support is available out of the box. Once installed, you should just be able to run the Makefile and you'll get bootable disk images for the Commodore 64 (with 1541 drive) and BBC Micro (producing a 200kB SSSD DFS disk):

make LLVM=<your llvm-mos bin directory here>/ -j$(nproc)

Building CP/M-65 is a bit of a performance because it's aggregating lots of other software, all of which need building in turn. You'll need: a C and C++ compiler, cc1541 (for creating 1541 disk images), cpmtools (for creating CP/M disk images), libfmt (all the C++ tools use this), python3 (for the build system), and FreePascal (because the MADS assembler is written in Pascal). Use these Debian packages:

cc1541 cpmtools libfmt-dev python3 fp-compiler srecord

There are also automated tests which use mame to emulate a reasonable number of the platforms, to verify that they actually work. To use this, install mame, and then run scripts/get-roms.sh to download the necessary system ROMs. Then do:

make LLVM=<your llvm-mos bin directory here>/ -j$(nproc) +mametest

You can add +all to that if you want to do a normal build and run the tests at the same time.

BBC Micro notes

• To run, do SHIFT+BREAK.

• Alternatively, if you're on a Tube system, do:

  MODE 3
  *!BOOT

• Alternatively alternatively, if you're on a Master system, do:

  MODE 131
  *DISK
  *!BOOT

• It'll autodetect the amount of available memory. If you're not on a Tube or Master system with shadow RAM, then your screen mode will consume TPA space. On a stock BBC Micro it will run in mode 0, but you'll only get a 2.5kB TPA! Mode 7 will work better here. It will work on the Electron, but you'll have to use mode 6 which will leave you 14kB of TPA. That's unfortunately not enough to run the assembler.

• The CP/M file system is stored in a big file (called cpmfs). This will expand up to the size defined in diskdefs: currently, 192kB (the largest that will fit on a SSSD disk). All disk access is done through MOS so you should be able to use a ramdisk, hard disk, Econet, ADFS, VDFS, etc. If so, you'll want to define your own disk format and adjust the drive definition in the BIOS to get more space.

• The BBC Micro port has a SCREEN driver.

Commodore 64 notes

• Load and run the CPM program to start.

• It's excruciatingly slow as it uses normal 1541 disk accesses at 300 bytes per second. Everything works, but you won't enjoy it. At some point I want to add a fastloader.

• The disk image produced is a hybrid of a CP/M file system and a CBMDOS file system, which can be accessed as either. The disk structures used by the other file system are hidden. You get about 170kB on a normal disk.

• Disk accesses are done using direct block access, so it won't work on anything other than a 1541 (but it should be straightforward to add support for other drives). Sorry.

VIC-20 notes

• See the Commodore 64 above.

• You need a fully expanded VIC-20 with all memory banks populated, for the full 35kB.

• You get a 40x24 screen, emulated using a four-pixel-wide soft font. It doesn't look great but is surprisingly readable, and is vastly better than the VIC-20's default 22x24 screen mode.

• Disk accesses are slightly faster than the Commodore 64, but only just. It's still a miserable experience.

Commodore PET notes

• You need a PET 4032, 8032 or 8096 and either a 4040 disk drive or something else which supports the same geometry. The disk image is for a 35-track SSSD system (I made it with cc1541). Adapting it for other drives should be easy.

• The 4032 is set up for the Graphics Keyboard. The 8032 and 8096 are set up for the Business Keyboard. (It would also be trivial to emulate the Business Keyboard on the Graphics Keyboard, but that is likely to be confusing.)

• It's much faster than the Comodore 64 --- you can run the assembler in real time without having to worry about retirement.

• It supports drive 0: only.

• This port runs completely bare-metal and does not use any ROM routines.

• The PET port has a SCREEN driver.

Commander X16 notes

• To use, place the contents of the x16.zip file on the X16's SD card. Load and run the CPM program to start.

• The CP/M filesystem is stored in a big file called CPMFS. It needs support for the Position command in order to seek within the file. x16emu currently doesn't support this in its host filesystem, so you'll need to use an actual SD card image. (I have a pull request outstanding to add support. An SD2IEC should work too, as these support the same commands. However a real Commodore disk drive will not work.

Apple IIe notes

• To use, place the contents of the appleiie.po file onto a disk and boot it. The disk image has been munged according to ProDOS sector ordering.

• It supports a single drive on slot 6 drive 1. You need a 80-column card (but not any aux memory).

• This port runs completely bare-metal and does not use any ROM routines.

Atari 800 XL/XE notes

• Standard 720 sectors single-sided single-density disk. The first track is reserved (18 sectors). The rest contains a standard CP/M 2.2 filesystem. Boot with BASIC disabled. This one runs on any Atari with at least 16kB of RAM.

• Or a 1MB harddisk image for use with drive emulators like SIO2SD, RespeQT, SDrive, AVG Cart etc... You can also mount it off a FAT partition with an SIDE2/3 cartridge and boot from there. That's almost emulation speed on real hardware. This one comes in two flavors. The hd version runs on any Atari with at least 16kB of RAM, the xlhd version is tailored for the XL/XE with at least 64kB of RAM. BIOS, BDOS and CCP live "under" the Atari OS ROM, which leaves over 49kB of TPA.

• Console is standard 40x24. It has a SCREEN driver.

• User area 1 contains loadable fonts and a utility to set a new console font (setfnt.com). This consumes at least 1kB of TPA (depending on the padding needed for alignment), but shows proper glyphs like curly braces and tilde.

• It also contains a loadable software 80 columns driver called tty80drv.com. This will cost you 7kB of TPA for driver code, font data, and screen memory. It has a full SCREEN implementation, too.

Oric notes

• This disk image is a MFM_DISK format disk as used by Oricutron. (If you need a simple sector image, look at .obj/oric.img.) You get about 350kB on a disk. The CCP, BIOS and BDOS all live in overlay RAM, leaving the entire user memory available for programs.

• If you're trying to run this on an Oric 1, you need the full upgrade to 64kB (including overlay RAM).

• Only the Microdisc interface currently works. (It's supposed to work with Jasmin too, but with Oricutron it boots but the keyboard is unresponsive, and on MAME it boots into BASIC, and I don't know why.) Only the first drive is supported. This would be easy to extend if anyone's interested.

• The console is 40x28. It has a SCREEN driver.

• The port runs completely bare-metal and does not use any ROM routines.

Sorbus notes

• The Sorbus Computer is a simple, open and cheap (<$15) machine to learn about the 65(C)02 processor. It combines an original CPU with a Raspberry Pi RP2040 microcontroller that implements all the rest (like RAM, I/O, and clock).

• For building a full image, it is also possible to copy the compiled binaries into the proper position into the source tree, and just run a global build.

• More info is available here:

  • Homepage with lightning talk
  • Source code on github

neo6502 notes

• The neo6502 is a W65C02-based computer using emulated hardware implemented by a RP2040. This can be programmed with various different firmware packages, each emulating a different 6502-based microcomputer. This port is intended for the native firmware package for the neo6502, Morpheus. (The other ports will work if you install the appropriate emulation firmware package.)

• It is ridiculously fast.

• To use, unzip the cpm65.zip file into the root directory of the USB stick or other storage card. Then enter load "cpm65.neo" at the prompt. CP/M-65 will run.

• To run on the emulator, either load it as above, or boot it directly with neo cpm65.neo@8000 run@8010.

• This port uses an emulated BDOS, meaning that it stores its files as FAT files on the neo6502's USB stick. Most well-behaved CP/M-65 programs will work, but anything which tries to access the raw filesystem won't; such as STAT or DINFO. Files for each drive and user are stored in separate subdirectories. All 16 drives are supported (in directories A to O).

• Drive B (i.e. /B/ on the storage device) contains some neo6502-specific utilitied. This are in no way complete, or documented.

• The console is 53x30. It has a SCREEN driver.

nano6502 notes

• The nano6502 is a 65C02-based SoC for the Tang Nano 20K FPGA board.

• The CPU is running at 25.175 MHz (i.e. the pixel clock).

• It is using CPMFS directly on the microSD-card, with 15x1Mb partitions (drives A to O).

• The text output is over HDMI, with 640x480 video output and a 80x30 console. It has a SCREEN driver.

• The input is currently using the built in USB serial port. This way, this port can be run with only the Tang Nano 20K board without any specific carrier board.

• To use, write the nano6502.img file into the SD-card using dd or your preferred SD-card image writer. If you are updating the image and want to preserve the data on all drives except A, write the nano6502_sysonly.img instead.

• User area 1 on drive A contains utilities for setting the text and background colors, and a demo application which blinks the onboard LEDs.

KIM-1 with K-1013 FDC notes

• To run this on an KIM-1, you need an MTU K-1013 Floppy Disk Controller with an SSDD 8'' disk (or this Pico based RAM/ROM/Video/FDC card) and full RAM upgrade, including the 0x0400-0x13ff memory hole.

• To use it, transfer the diskimage.imd image to an SSDD 8'' disk (or place it directly onto an FAT or exFAT formatted SD card and assign it to disk0 in the Pico card). Start the KIM-1 in TTY mode, load the boot.pap loader program into 0x0200 and execute it.

• Only 1 disk is supported. Multi-disk is not stable in CP/M-65 yet.

• Only TTY interface for now, no SCREEN driver.

KIM-1 with directly attached SD card notes

• This port uses Ryan E. Roth's sdcard6502 for the PAL-1, which in turn is based on George Foot's sdcard6502 for Ben Eater's 6502 computer.

• You'll need an SDHC card of any capacity (only 32MB are used) and a generic Arduino SD card adapter with 5V to 3.3V conversion. See the links above for detailed requisites and connection instructions.

• To use it, transfer the diskimage.raw file to the SD card using dd. Balena Etcher also works in Windows, just ignore the "not a bootable image" warning. Start the KIM-1 in TTY mode, load the bootsd.pap loader program into 0x0200 and execute it.

• For KIM-1 clones, you can place the bootloader into the free space of the KIM-1 rom. Write the contents of the bootsd-kimrom.bin file at 0x1AA0 (or 0x2A0 relative to the KIM-1 rom). This romable loader has two entry points:

  • 0x1AA0 is for cold start, that is, you can point the 6502 reset vector to 0x1AA0 if you want to start CP/M-65 at reset. In this case, the TTY is initialized to 9600 bauds, so make sure that your terminal is configured to that speed.
  • 0x1AB2 is for booting from the KIM monitor

• For the KIM-1, at least a 32KB (56KB recommended) RAM expansion from 0x2000 is required, as well as RAM filling the 0x0400-0x13ff memory hole. The BIOS assumes that at least the required RAM is installed, and checks for extra RAM above 0xA000.

• Same requisites apply to the PAL-1 and, additionally, the second 6532 expansion board.

• 1 32MB disk supported.

• Only TTY interface for now, no SCREEN driver.

KIM-1 with Commodore 1541 drive

• Based on the C64 port, so same notes apply.

• This port needs the xkim1541 extensions for the KIM-1 installed at 0xF000. The PAL-1 is also supported, and needs the same extensions but installed at 0xDA00, as modified by Neil Andretti.

• If you also have my modified xKIM monitor, then load the CPM program and jump to address 0x6000.

• If not, load the bootiec-kim or bootiec-pal bootloader into 0x200 and execute it.

Supported programs

Commands include DUMP, STAT, COPY, SUBMIT, ASM, QE and BEDIT plus some smaller utilities. I'd love more --- send me pull requests! The build system supports cc65 assembler and llvm-mos C programs. The native assembler can be used (in emulation) to cross compile programs for CP/M-65.

In the CCP, you get the usual DIR, ERA, REN, TYPE and USER. There is no SAVE as on the relocatable CP/M-65 system assembling images in memory is of questionable utility, but there's a new FREE command which shows memory usage.

You also get a port of Altirra BASIC, an open source Atari BASIC clone. This is called ATBASIC. See below for more details.

Pokey the Penguin loves to read your pull requests!

The assembler

The CP/M-65 assembler is extremely simple and very much customised to work for the CP/M-65 environment. It operates entirely in memory (so it should be fast) but it's written in C (so it's going to be big and slow). It's very very new and is likely to have lots of bugs. There is, at least, a port of the DUMP program to it which assembles, works, and is ready to play with.

Go read cpmfs/asm.txt for the documentation.

The BASIC

Altirra BASIC is an open source recreation of the BASIC used on the Atari 8-bit machines (on which CP/M-65 runs, coincidentally). It has been heavily modified by me to work on CP/M-65. Anything Atari-related has been removed, including graphics, sound, etc. In addition, I have extended the error reporting, added support for case-insensitive keywords (simply because Atari BASIC traditionally requires upper case but most CP/M-65 platforms don't have caps lock keys!), and fairly crudely added file I/O support. There is no screen editor. It is (should be) binary compatible with Atari BASIC, although programs using Atari features which aren't supported will of course not run.

It is currently rather fragile with a number of known (and, probably, unknown) bugs. Please file bug reports!

Atari BASIC is rather different from Microsoft BASIC. Please consult the user manual.

Important! Do not contact the author of Altirra BASIC for anything related *to the CP/M-65 port! Any bugs are strictly my fault.

The editors

BEdit is an incredibly simple line editor modelled after a basic interpreter (command entry, with LOAD, SAVE, LIST, line numbers etc). It's written in machine code and assembled with the CP/M-65 assembler; you can assemble it locally if you have a system with 30kB or more TPA. It'll run on all platforms.

Go read cpmfs/bedit.txt for the documentation.

QE is a much less simple vi-inspired screen editor, written in C. it's much more comfortable to use than BEDIT, but is about five times the size, and will only run on systems with a SCREEN driver, as noted above (you can also use the DEVICES command to see what devices your system supports).

The Pascal

Pascal-M is a Pascal subset intended for use on very small machines. It compiles to bytecode, M-code, which is then run with an interpreter. The compiler is itself written in Pascal-M and is capable of compiling itself (very slowly). There is a basic port to CP/M-65.

To use it, you need to use the interpreter, PINT, to run the compiler to compile your program into an OBP file. This is then translated into an OBB file by PLOAD (not written in Pascal!). You can then run the resulting OBB file with PINT. For example:

A> PINT PASC.OBB HELLO.PAS HELLO.OBP
A> PLOAD HELLO.OBP HELLO.OBB
A> PINT HELLO.OBB

The compiler will also generate a PROGRAM.ERR file containing a copy of any error messages that result from the compilation process.

Sadly, you need at least 36kB of free RAM to run the compiler, and also the disk images for various systems are full, so it's only included for a few platforms.

Pascal-M is considerably simplified from the full Pascal language, with support for only 16-bit integers, but it does support records, sets, enumerations, pointers, nested functions and procedures, etc. Performance isn't brilliant but it does work. CP/M-65 is very basic, consisting of support for text files using the traditional assign/reset/rewrite/close API. You can have as many open at once as you like but you can't seek inside a file. In addition, while new is supported, there is no dispose.

For more information on Pascal-M, see Hans Otten's website. However, do not report bugs on the CP/M-65 port to him --- file bug reports here instead.

Utilities

bin/cpmemu contains a basic CP/M-65 user mode emulator and debugger. It'll run programs on the host environment with an emulated disk, which is very useful for testing and development. To use:

./bin/cpmemu .obj/dump.com diskdefs

Add -d at the front of the command line to drop into the debugger --- use ? for basic help. It can only access 8.3-format all-lowercase filenames in the current directory, but you can also map drives. Use -h for help.

Who?

You may contact me at dg@cowlark.com, or visit my website at http://www.cowlark.com. There may or may not be anything interesting there. The CP/M-65 project was designed and written by me, David Given.

License

Everything here so far except the contents of the third_party directory is © 2022-2023 David Given, and is licensed under the two-clause BSD open source license. Please see LICENSE for the full text. The tl;dr is: you can do what you like with it provided you don't claim you wrote it.

The exceptions are the contents of the third_party directory, which were written by other people and are not covered by this license. This directory as a whole contains GPL software, which means that if you redistribute the entire directory, you must conform to the terms of the GPL.

third_party/lib6502 contains a hacked copy of the lib6502 library, which is © 2005 Ian Plumarta and is available under the terms of the MIT license. See third_party/lib6502/COPYING.lib6502 for the full text.

third_party/tomsfonts contains a copy of the atari-small font, which is © 1999 Thomas A. Fine and is available under the terms of a minimal free license. See third_party/tomsfonts/LICENSE for the full text.

third_party/altirrabasic contains a hacked copy of Altirra Basic, which is © 2014 Avery Lee and is available under the terms of a minimal free license. See third_party/altirrabasic/LICENSE.md for the full text.

third_party/mads contains a copy of Mad Assembler, which is © 2018-2023 Tomasz Biela and is available under the terms of the MIT license. See third_party/mads/LICENSE for the full text.

third_party/pascal-m contains a extremely hacked up copy of the Pascal-M bytecode compiler and interpreter, which is © 1978-2021 Niklaus Wirth, Mark Rustad and Hans Otten and is available under the terms of the MIT license. See third_party/pascal-m/LICENSE for the full text.