A JavaScript Gameboy Assembler

gbasm is a JavaScript based compiler for Gameboy z80 assembly code.

gbasm is mainly being developed for and tested with Tuff.

Installation and Usage

1. Install Node.js
2. Now install gbasm by running npm install -g gbasm

Usage: gbasm [options] [sources]

   --outfile, -o <s>: The name of the output rom file (default: game.gb)
      --optimize, -O: Enable instruction optimizations
   --mapfile, -m <s>: Generates a ASCII overview of the mapped ROM space
   --symfile, -s <s>: Generates a symbol map compatible with debuggers
  --jsonfile, -j <s>: Generates a JSON data dump of all sections with their data, labels, instructions etc.
        --silent, -S: Surpresses all logging
         --debug, -d: Enable support for custom "msg" debug opcodes',
       --verbose, -v: Surpresses all logging
           --version: Displays version information
              --help: Displays this help text

Output Options

• __ --outfile / -o __

  Specifies the filename of the generated ROM image.

• __ --optimize / -O __

  Turns on assembly optimizations which are automatically performed during linkage.

• __ --mapfile / -m__

  Generates a ASCII overview of the mapped ROM areas.

• __ --symfile / -s __

  Generates a symbol map file for use with Debuggers (e.g. bgb)

• __ --debug / -d __

  Enables support for custom msg opcodes for use with Debuggers (e.g. bgb)

  ; This will log "Debug Message" when run in the debugger
  msg "Debug Message"

  Note: The msg opcode will be ignored when compiling without the flag.

• __ --jsonfile / -j __

  Generates a json file that contains the fully linked ROM data serialized into a detailed format useable for further, custom processing.

Compatibility Notes

gbasm is mostly compatible with rgbds but there are some deviations and additions:

General

• gbasm is a multipass compiler, meaning the all sources files and definitions are parsed before resolving any names or sizes.

Syntax

• The load accumulator and increment/decrement hl type instructions only take hli and hld as their second operand
• Memory operands do only support [ and ] in their syntax
• All names and labels which start with an underscore are treated as being local / private to the file they were defined in

Macros

• Most of the pre-defined macros from rgbds are available (e.g. COS, STRLWR etc.)

• User defined macros come in two flavors:

  1. Expression Macros

  These macros contain only a single expression statement and can be used as values everywhere a built-in macro could be used:

  MACRO add(@a, @b)
    @a + @b
  ENDMACRO
  
  DB add(2, 5) ; essentially DB 7

  Expression Macros can take Numbers and Strings as their arguments.

  2. Expansion Macros

  These are macros in the classical sense which just expand into additional assembler code:

  MACRO header()
    DB $11,$22,$33,$44,$55
    DW $1234,$4567
  ENDMACRO
  
  header(); expands into the DB and DW diretives above

  In addition to Strings and Numbers, expansion macros can also take Registers as their arguments.

  MACRO ld16(@number, @a, @b)
    ld @a,@number >> 8
    ld @b,@number & $ff
  ENDMACRO
  
  ld16($1234, b, c); turns into ld b,$12 and ld c,$34

Instructions

gbasm supports additional meta instructions at the source code level, which will be compiled down to multiple native instructions.

These aim at increasing the readability of the source.

addw

Adds a 8-bit operand to a 16-bit register using only the Accumulator:

; ld      a,$ff
; add     a,l
; ld      l,a
; adc     a,h
; sub     l
; ld      h,a
addw  hl,$ff
addw  bc,$ff
addw  de,$ff

; add     a,l
; ld      l,a
; adc     a,h
; sub     l
; ld      h,a
addw  hl,a
addw  bc,a
addw  de,a

; ld      a,reg
; add     a,l
; ld      l,a
; adc     a,h
; sub     l
; ld      h,a
addw  hl,reg
addw  bc,reg
addw  de,reg

incx

Extended increment of a memory address, using the Accumulator as an intermediate register (destroying its contents):

; ld a,[$0000]
; inc a
; ld [$0000],a
incx [$0000]

decx

Extended decrement of a memory address, using the Accumulator as an intermediate register (destroying its contents):

; ld a,[$0000]
; dec a
; ld [$0000],a
decx [$0000]

ldxa

Extended memory loads using the Accumulator as an intermediate register (destroying its contents):

; ld  a,[hli]
; ld  R,a
ldxa  b,[hli]
ldxa  c,[hli]
ldxa  d,[hli]
ldxa  e,[hli]
ldxa  h,[hli]
ldxa  l,[hli]

; ld  a,[hld]
; ld  R,a
ldxa  b,[hld]
ldxa  c,[hld]
ldxa  d,[hld]
ldxa  e,[hld]
ldxa  h,[hld]
ldxa  l,[hld]

; ld  a,R
; ld  [hli],a
ldxa  [hli],b
ldxa  [hli],c
ldxa  [hli],d
ldxa  [hli],e
ldxa  [hli],h
ldxa  [hli],l

; ld   a,R
; ld   [hld],a
ldxa  [hld],b
ldxa  [hld],c
ldxa  [hld],d
ldxa  [hld],e
ldxa  [hld],h
ldxa  [hld],l

; ld  a,$ff
; ld  [$0000],a
ldxa  [$0000],$ff

; ld  a,$ff
; ld  [hli],a
ldxa  [hli],$ff

; ld  a,$ff
; ld  [hld],a
ldxa  [hld],$ff

; ld  a,R
; ld  [$0000],a
ldxa  [$0000],b
ldxa  [$0000],c
ldxa  [$0000],d
ldxa  [$0000],e
ldxa  [$0000],h
ldxa  [$0000],l

; ld  a,[hli]
; ld  [$0000],a
ldxa  [$0000],[hli]

; ld  a,[hld]
; ld  [$0000],a
ldxa  [$0000],[hld]

; ld  a,[$0000]
; ld  [$0000],a
ldxa  [$0000],[$0000]

; ld  a,[$0000]
; ld  R,a
ldxa  b,[$0000]
ldxa  c,[$0000]
ldxa  d,[$0000]
ldxa  e,[$0000]
ldxa  h,[$0000]
ldxa  l,[$0000]

; ld  a,[$0000]
; ld  [hli],a
ldxa  [hli],[$0000]

; ld  a,[$0000]
; ld  [hld],a
ldxa  [hld],[$0000]

License

Licensed under MIT.