By Pierre Sarrazin

CMOC is a 6809-generating cross-compiler for a subset of the C language. It produces assembler code for the Motorola 6809 processor in the Color Computer .BIN format, the Dragon computer, as well as the Motorola SREC and Vectrex formats. It runs under GNU/Linux and other Unix-like environments like Darwin and Cygwin. It requires the LWTOOLS assembler (lwasm) and linker, by William Astle.

The most significant difference between CMOC and a complete C compiler is the absence of bit fields and of a complete Standard C library. Floats are only usable under Color Basic. CMOC comes with a small library that serves as a starting kit.

CMOC is free software distributed under the GNU General Public License, version 3 or later, except for the files of the USim simulator, which is used for testing.

The current version is 0.1.59. It was released on 2019-06-03.

Release notes for 0.1.59:

Release notes for 0.1.58:

  • The main() return value, and the exit() argument, are now guaranteed to be returned in D upon exiting the program, when compiled for CoCo Basic or for the Dragon.
  • Floating point and long constants are now only emitted when they are used by emitted code. This resolves double emissions that could happen with an array of constants of those types.
  • 16-bit multiplications by 10 are now optimized by the use of a specialized utility routine.
  • Several minor bug fixes.

Release notes for 0.1.57:

  • Reimplemented rand() as an Xorshift random number generator to reduce the predictability of each of the 15 bits returned. The previous implementation returned numbers that alternated between even and odd.
  • Fixed comparisons involving a signed byte and an unsigned 8-bit constant.
  • Modified optimization "storeLoad" so that a load of an absolute address is assumed to deal with a volatile memory location, like an I/O port.

Release notes for 0.1.56:

  • CMOC now directly supports the generation of Dragon executables.
  • Added itoa(), utoa(), ltoa() and ultoa() to the standard library (declared in ), although only base 10 is supported at this time.
  • Fixed bad code generation in the case of a subtraction of a pointer from an array name.
  • Fixed a bug that prevented a program from subtracting a value of type T[] from a value of type const T *.
  • readJoystickPositions() does not turn the audio back on anymore after reading the positions.

I can be contacted (in French or English) at sarrazip at sarrazip dot com. (Questions regarding Vectrex-specific issues should be addressed to Johan Van den Brande.)



See MD5, SHA1 and SHA512 for signatures of these and other files.

Libraries and sample programs

The "🐲" icon means that the program or library is compilable and usable on the Dragon computer.

decbfile (0.1.2) (Public domain)

Library that offers read/write access to files on a floppy disk in the Disk Basic format. It uses Disk Basic's sector routine by default, but can be made to use a stand-alone version, therefore making Basic's presence unnecessary.

This version, published on 2019-02-28, fixes:

  • a bug in dskcon_processSector() that allowed the modification of CMOC-reserved registers upon returning;
  • a bug in decb_findDirEntry() that could keep it from finding a free directory entry;
  • a bug that disallowed 0 as a sector buffer address;

Also loadbin.c has been added: it is a demo that loads a .bin file and executes it.

BGraph (0.1.1) (Public domain)

Graphics library that offers functions similar to Basic's LINE, DRAW and PAINT commands. It does not assume the presence of the Color Basic interpreter. 🐲

BSound (0.1.1) (Public domain)

Library that offers a function similar to Basic's PLAY command. It does not assume the presence of the Color Basic interpreter. 🐲

BControl (0.1.1) (Public domain)

(Published 2019-06-03.) Library that offers functions similar to Color Basic's INKEY$, JOYSTK and BUTTON. It does not assume the presence of the Color Basic interpreter. It can be compiled for OS-9 (althbough only the keyboard is supported as of this version). 🐲

Color Eights (0.1.12) (GPLv3)

A card game derived from Crazy Eights that I wrote with CMOC. Uses the Cardgame library (see below). It can be run both under Disk Basic and NitrOS-9 EOU (from a 32x16 terminal). 🐲

Cardgame (0.1.9) (Public domain)

A card game library. Contains the generic code used by my Color Eights game: drawing and erasing cards (32x42 pixels), and drawing text (uppercase 32x24 grid), in a PMODE 4 screen. Beep and "white noise" functions. Rename cardgame.c to something else, fill main() and code other functions. The 8x8 text font can be reused independently, as done by cc3dblb (see below). This library can be compiled for OS-9, but the sound features are not supported as of this version. 🐲

cc3dblb (0.1.1) (Public domain)

A skeleton for a CoCo 3 double-buffering game. Start a new game project by renaming the files, then recode the onFlip() function. Uses the 8x8 text font from the Cardgame library to print text on the graphics screen. Requires Cardgame and BGraph (see above).

DwTerm (by Michael Furman)

A DriveWire 4 Terminal Program for the Disk Basic environment. Can be used with other DriveWire-related programs written by Michael.

CoCo MiniLisp (by Jamie Cho)

A port of Rui Ueyama's MiniLisp. Version 0.5.0, released in October 2017, uses CMOC's support for 32-bit arithmetic.

xdaliclock port (by Jamie Cho)

A port of Jamie Zawinski's xdaliclock to the CoCo.

Splinter (by Jamie Cho)

A CoCo 3 break-the-bricks video game written by Jamie Cho with CMOC. Splinter features colorful 320x192 graphics and smooth animation.

hirestxt: 51x24 and 42x24 text screens (0.3.1) (Public domain)

A library that redirects printf() to a software 51x24 or 42x24 black-on-green PMODE 4 text screen. (A sample program is included.) Optionally supports several VT52 terminal sequences (disable this with #define HIRESTEXT_NO_VT52). Useful to get true lowercase, including Latin-1 accented characters, on all CoCos. 🐲

Color Verbiste (0.1.5) (GPLv3)

A partial CoCo port of my French conjugator. Requires hirestxt. There is a precompiled disk image. Details on the Verbiste home page and its CoCo section.

nobasic (0.1.9) (Public domain*)

A program that puts the CoCo in all-RAM mode, overwrites the Basic interpreter, moves the program and the stack to the end of the 64K of RAM and redirects the 60 Hz interrupt, as an example of a program that can use the entire 64K of RAM. Contains a disk sector read demo and a CoCo 3 graphics demo. This version requires CMOC 0.1.51 or later, as it is split in two C files (nobasic.c and dskcon.c) and uses the const keyword. *Some code in dskcon.c comes from DECB. 🐲

bigapp (0.1.0) (Public domain)

A demo of a program that is too large to be loaded by Basic's LOADM command and uses the whole 64K of RAM. This demo also adds arbitrary data files (PMODE 4 screens) to the .bin so that this data gets loaded with the code. The user calls LOADM and EXEC on a small loader program that takes care of loading the large program. Requires a 64K CoCo and the decbfile library, available on this page.

autostart.c (0.1.2) (Public domain)

A program to be compiled as a boot loader that goes on track 34, so that the CoCo's DOS command will execute it. (The autostart.bin file is not meant to be loaded with LOADM.) The program feeds Color Basic's console input with the command RUN"*.BAS" in order to run that Basic program automatically. Install this on a disk image with this command: install-coco-boot-loader foo.dsk autostart.bin

FuncPlot (0.2.3) (GPLv3)

Demo program that plots a mathematical function in PMODE 4 graphics. The program implements an expression parser and an RPN interpreter to evaluate the user's function across an interval. Requires hirestxt and BControl. 🐲

Demo of Basic variable access from a CMOC program (Public domain)

(Updated 2018-04-03.) This archive contains a .dsk image file that contains VARPTR.BAS and VARPTR.BIN. Type RUN"VARPTR" on a CoCo. The archive also contains the C source file, which is compilable under CMOC. The Basic and C listings can be studied to learn how to access Basic variables from a CMOC program.

parse-coco-bin (Public domain)

A Perl script that lists the blocks of a CoCo Disk Basic .BIN file, along with the entry point.

Bouncy Ball (by Lee Patterson)

A game for all CoCos. (It does not come with the source code.)

CoCoTair: an 8080 emulator (by Mark Sherman)

This was Mark's Retrochallenge in 2017. This emulator can be used to run Altair BASIC.


See the manual that comes with CMOC.

As of November 2018, I am developing CMOC on an Ubuntu 14.04 GNU/Linux system using GCC 4.8.4.

Building on Windows

CMOC cannot currently be compiled directly as a native Windows application, but it can be compiled under Cygwin. It has been shown to work under that Unix-like environment.

Cygwin is recommended over MinGW, where the pipe calls (popen()) do not behave as expected, as of Fall 2018. In particular, the apostrophes on the command lines composed by CMOC, when calling the C preprocessor, do not appear to be interpreted as they should by the shell called by popen().

Note that LWTOOLS should then also be compiled for Cygwin. Packages that were pre-built for Windows or MinGW will probably not work as CMOC expects.

Building on Mac OS X

The configure script should recognize that it is running on a Mac OS X system, but if it does not, the following instructions may help.

Thanks to Jamie Cho for these Mac instructions.

Glen Hewlett has posted an article on his blog about using CMOC from Mac OS or Linux.

Other resources

Last update to this page: 2019-06-03 23:32:15 EST5EDT