as09

This project is an MC6809 cross assembler. It is written in portable C using yacc/bison for the parser and a handwritten lexical analyzer. The code is parsed in a single-pass using a fixup mechanism to back-patch forward references to symbols.

The main goal of this project was to create a cross assembler compatible with EDTASM+ syntax for the TRS-80 Color Computer. To that end the assembler can create binary output files compatible with the TRS-80 Disk Extended Color Basic loader using the -b command line option.

While many such cross assemblers already exist, I wanted to retain the option to extend the assembler for my own purposes.

A secondary goal of this project was to enable the generation of output files to enable FPGA emulation of the 6809. Using the -r command line option a Verilog synchronous ROM file. Using the -a option will generate an async ROM file in verilog. The -s option will generate a file that uses System Verilog. Finally, the -x option will generate an Intel format .hex file.

The assembler is routinely built and tested on Windows, Mac, Linux and RPi. It has been proven through compilation and execution of significant assembly language code bases on both the XROAR emulator and working CoCo 1 machines.

If you find any code generation bugs please report them!

This project pairs with my dsktools project. The dsktools application enables creation of RS-DOS compatible virtual disk (.DSK) files which can be loaded in CoCo emulators like XROAR or physical machines via CoCo SDC.

6809 Assembly

The as09 assembler follows the Motorola MC6809 and EDTASM+ syntax which you can find documented here.

There are some portions of Disk EDTASM+ that are not supported. Specifically:

• Line numbers
• Save and load commands
• Conditional compilation
• Emulation and debugging

And there are some new, more modern, assembler features that are not present in Disk EDTASM+ like:

• Labels require a following ':'
• Additional pseudo-instructions
• Additional c-style expression operators

Assembler extensions

as09 adds several optional instruction extensions for convenience. They are:

Mnemonic	Description
ASLD	equivalent to ASLB followed by ROLA
ASRD	equivalent to ASRA followed by RORB
BNZ	equivalent to BNE
BZ	equivalent to BEQ
CLRC	Clear carry flag, equivalent to ANDCC #$FE
CLRD	equivalent to CLRA followed by CLRB
CLRZ	Clear zero flag, equivalent to ANDCC #$FC
FCZ string	Declares a null terminated string
INCLUDE string	Includes file in assembly
SETC	Set carry flag, equivalent to ORCC #$01
SETZ	Set zero flag, equivalent to ORCC #$04

The parser for as09 enables a few modern features like C-style backslash character processing in strings. For example, use \r in a string to include a carriage-return.

Other C-style operators that can be used in expressions include the bitwise AND &, OR | and NOT ~ operators.

Using as09

Using the assembler is straightforward. Here is a small example program for the TRS-80 CoCo that prints out a string on the screen.

;---------------------------------------------------
; Hello World for the TRS-80 CoCo in MC6809 assembly
;---------------------------------------------------
CHARIN EQU $A000
CHAROUT EQU $A002

STRING: FCC 'Hello World!' FCB 0

START:
  LDX #STRING    ; get ptr to string

LOOP:
  LDA ,X+        ; get next character
  BEQ DONE       ; if null terminator then done

  JSR [CHAROUT]  ; print out next char
  BRA LOOP       ; do it again

DONE:
  JSR [CHARIN]   ; poll keyboard
  BEQ DONE       ; wait for keypress
  SWI            ; quit
END START

Save that code to a file called hello.asm and assemble it as follows:

% as09 hello.asm
as09 v0.5.0 - an MC6809 assembler by Mark Seminatore (c) 2024
as09 assembled 33 bytes, 23 total lines of code to 'a.out'

To generate a binary file ready to execute on the CoCo use the -b option along with -o to name the file. For example

% as09 -b -o hello.bin hello.asm
as09 v0.5.0 - an MC6809 cross-assembler by Mark Seminatore (c) 2024
as09 assembled 33 bytes, 23 total lines of code to 'hello.bin'

Building as09

You can build as09 using either Makefile or CMake. For makefile builds use:

% make

For CMake builds:

% mkdir build
% cd build
% cmake ..
% cmake --build .

Installing as09

For Unix-like systems a shell script is provided that will install a link to the as09 binary in the /usr/bin/local folder. You can invoke this using Make or by running the file links.sh directly.

% make install

OR

% sudo ./links.sh

Testing as09

If you make modifications to as09, particularly ones that change the code generation you must run the test cases. These compare the hex file output of the test.asm file vs. the baseline file test.hex. If there are any changes then a code generation error may have been introduced.

The tests can be run via Make or CMake. For makefile usage:

% make test

Or for Cmake projects:

% cd build
% ctest