Ophis/platform/c64_0.oph

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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; Commodore 64 Basic Runtime File
;;
;; Include this at the TOP of your C64 program, and it will handle
;; hiding away the BASIC ROM and data and restoring it at the end.
;;
;; You will have a contiguous block of RAM from $0800 to $CF81, and
;; Zero Page access from $02 to $7F in the segment "zp".
.word $0801
.org $0801
; BASIC program that just calls our machine language code
.scope
.word _next, 10 ; Next line and current line number
.byte $9e," 2062",0 ; SYS 2062
_next: .word 0 ; End of program
.scend
.data zp ; Zero Page memory segment.
.org $0002
.text
.scope
; Cache BASIC zero page at top of available RAM
ldx #$7E
* lda $01, x
sta $CF81, x
dex
bne -
; Swap out the BASIC ROM for RAM
lda $01
and #$fe
ora #$06
sta $01
; Run the real program
jsr _main
; Restore BASIC ROM
lda $01
ora #$07
sta $01
; Restore BASIC zero page
ldx #$7E
* lda $CF81, x
sta $01, x
dex
bne -
; Back to BASIC
rts
_main:
; Program follows...
.scend