Hello World

2023-09-29

Write your c64 ASM code

  • The syntax is roughly modelled on that of TASS64, but only for the fundamentals i.e.
    • * refers to current address location, and can be read from or written to
    • All programs should start with a *=.... line to set the starting address
    • .byte values must be hexadecimal only, and single byte hexadecimal must always include 2 characters. i.e. $0e will work, but $e won’t work.
    • Similarly, for immediate values. i.e. #$01 will work. #$1 won’t work.
library(c64asm)

asm <- '
*=$0801
  .byte $0c, $08, $0a, $00, $9e, $20
  .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 in one step

  • If you’re willing to trust the compiler, then use c64asm::compile() to convert ASM into bytes.
  • Still have to extract the bytes from the prg_df data.frame to view and save.
prg <- c64asm::compile(asm)

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

Compile in multiple steps (for debugging purposes)

  • When debugging the output, you can manually run the compilation steps and view the output at each stage.
  • c64asm isn’t a complete or bug-free assembler by any means!
line_tokens <- c64asm::create_line_tokens(asm)

prg_df      <- c64asm::create_prg_df(line_tokens)
prg_df      <- c64asm::process_symbols(prg_df)
prg_df      <- c64asm::process_zero_padding(prg_df)

c64asm::extract_prg_bytes(prg_df)
#>  [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 code in an emulator 

library(c64vice)

# Start VICE with 'x64sc -binarymonitor'
# Then transfer bytes to VICE and run the program with the following:
c64vice::run_prg(prg)