dasm

The dasm macro assembler (for JavaScript)

This is an emscripten-compiled version of the dasm macro assembler.

The dasm macro assembler transforms assembly code into 6502-compatible executable binary code. Since this is a JavaScript port of dasm, it allows that compilation process from JavaScript programs; more especifically, it can be used to create Atari VCS 2600 and Fairchild Channel F ROMs from a string containing dasm-compatible assembly source code.

In other words, it turns something like this:

; Pick the correct processor type
        processor 6502
; Basic includes
        include "vcs.h"
        include "macro.h"
; Start address
        org $f000
; Actual instructions
start   SEI
        CLD
        LDX  #$FF
        TXS
        LDA  #$00
        ...

...into its equivalent byte code:

f000 78
f001 d8
f002 a2 ff
f004 9a
f005 a9 00
...

Technical information

This package uses version 2.20.11 of dasm. It supports the following processor architectures:

• 6502 (and 6507)
• 68705
• 6803
• HD6303 (extension of 6803)
• 68HC11

Among other features, dasm supports:

• fast assembly
• several binary output formats available
• expressions using [] for parenthesis
• complex pseudo ops, repeat loops, macros, etc

This specific port was built on Linux (err, Windows 10 bash) from the dasm source using the following commands:

emmake make
mv src/dasm src/dasm.bc
emcc src/dasm.bc -o dasm.js

The following changes were manually applied to the exported dasmj.js file:

1. Wrapped the code with a function, so that could export it as a module
2. Returned the created module as the result of a function call
3. Exposed its internal file system through a FS variable

Usage

import * as dasm from "dasm";

// Read utf-8 assembly source
const src = "...";

// Run with any number of parameters
const result = dasm(src, "-f1", "-ofile.out", "-lfile.lst", ...);

// Read the output as a binary (int array)
const ROM = result.FS.readFile("file.out");

More information

Please download dasm and check its full documentation for more information and command line switches.

Check the emscripten FileSystem to learn about FS and how to use it.

Todo

• More examples, including on how to include files
• Expose the module initialization options
• TypeScript definitions
• Real tests with CI
• Command-line package (dasm-cli)

Contributions are welcome.

License

This follows dasm itself and uses the GNU Public License v2.0.