createprg.rkt

#lang racket

;; Write a simple C64 assembly program to a PRG file, along with a line
;; of BASIC program to load the machine-language code.

;; The assembly program that will be run
(define program
  (bytes #xA9 #x00        ; LDA #00
         #x8D #x20 #xD0   ; STA $D020
         #x8D #x21 #xD0   ; STA $D021
         #x60))           ; RTS

;; The PRG file header (specifies the memory address of the code following)
(define prg-header (bytes #x01 #x08))

;; The BASIC loader, just a single line program:
;; 10 SYS 2064
(define loader
  (bytes #x08 #x0C            ; Pointer to next line of BASIC code
         #x0A #x00            ; Line number (000A = 10)
         #x9E                 ; byte-code for the SYS instruction
         #x20                 ; space
         #x32 #x30 #x36 #x34  ; 2064 (as string)
         #x00                 ; line terminator
         #x00 #x00))          ; pointer to next line of BASIC (0 = end program)

;; The file is just the header + loader + program
(define file-contents (bytes-append prg-header loader program))


;; write the file
(call-with-output-file "blkbrd.prg" #:mode 'binary
  (λ (out)
    (write-bytes file-contents out)))