c64tass

{c64tass} is a wrapper around TASS - a standard 6502 assembler used for developing for the c64.

Note: TASS and this package represent a compiler i.e. a way of turning c64 assembly into 6502 machine code. It does not execute the code or provide a c64 emulator for doing so.

For interfacing with a running VICE instance on a local machine see {c64vice}

What’s in the box

• The TASS R6 class with the following methods:
  • initialize(asm) with assembly text or file reference
  • compile() compile the assembly code using TASS
  • get_prg() get the compiled prg file as a raw vector

Installation

You will need to have TASS already installed on your machine to make use of this package.

On macOS using homebrew: brew install tass64

remotes::install_github('coolbutuseless/c64tass')

A simple 6502 program

The following c64/6502 ASM code will clear the screen and then write Hello #rstats! at the top

asm <- '
*=$0801
  .byte $0c, $08, $0a, $00, $9e, $20  ; 10 SYS 2080
  .byte $32, $30, $38, $30, $00, $00
  .byte $00

*=$0820
      lda #$93        ; Clear the screen
      jsr $ffd2

      ldx #$00        ; initialise the offset pointer into our message
loop  lda message,x   ; load a character and write it to screen 
      and #$3f        ; Manually place chars on screen
      sta $0400,x
      inx
      cpx #$0e
      bne loop

      rts

message
    .text "Hello #rstats!"
'

Compile the ASM to 6502 machine code.

library(c64tass)

tass <- TASS$new(asm = asm, tass_bin = "/opt/homebrew/bin/64tass")
tass$compile()
prg <- tass$get_prg()
prg

##  [1] 01 08 0c 08 0a 00 9e 20 32 30 38 30 00 00 00 00 00 00 00 00 00 00 00 00 00
## [26] 00 00 00 00 00 00 00 00 a9 93 20 d2 ff a2 00 bd 35 08 29 3f 9d 00 04 e8 e0
## [51] 0e d0 f3 60 c8 45 4c 4c 4f 20 23 52 53 54 41 54 53 21

Run c64 programs using VICE

There are a number of ways to run the compiled program:

• Save to physical media somehow and load on a real c64
• Save the prg data as raw bytes to a file and then load in VICE or any c64 emulator.
• Pipe the bytes directly into the memory of a running VICE emulator

The code below shows the third option i.e. write the prg into memory

library(c64vice)

# VICE must already be running with the binary monitor activated.
# .e.g.   `x64sc -binarymonitor`
c64vice::run_prg(prg)

c64-verse

Acknowledgements

• R Core for developing and maintaining the language.
• CRAN maintainers, for patiently shepherding packages onto CRAN and maintaining the repository