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; Memcheck needs to do this:
;1. If RAMTOP is >=$C0, go to step 6.
;2. Attempt to disable BASIC.
;3. Write some data to $A000, read it back (do twice with 2 different values)
;4. If we couldn't read back what we wrote, that means there really is a
; cartridge plugged in. Go to step 8.
;5. Set RAMTOP to $C0.
;6. Do a GRAPHICS 0.
;7. Exit via RTS, so the rest of the game will load.
;8. Do a GRAPHICS 0.
;9. Print a "remove cartridge" message
;10. Wait for a keypress
;11. Exit to DOS (without loading the rest of the file)
;At no point do we look at RAMSIZ, since it can't be trusted under SDX.
;Note that when we reach step 6, RAMTOP is always $C0 (either it was,
;or we set it to that).
; cl65 -o checkmem.xex -t none checkmem.s
.include "atari.inc"
start = $0600 ; use page 6 for now
; homebrew XEX header
.word $ffff
.word start
.word end-1
.org start
; message is "Need 48K, remove cartridge" in screen codes.
msg:
.byte $2e, $65, $65, $64, $00, $14, $18, $2b
.byte $0c, $00, $72, $65, $6d, $6f, $76, $65
.byte $00, $63, $61, $72, $74, $72, $69, $64
.byte $67, $65
msglen = * - msg - 1
S: .byte "S:",0
init:
;1. If RAMTOP is >=$C0, go to step 6.
lda RAMTOP
cmp #$c0
bcs ramtop_ok
;2. Attempt to disable BASIC.
; set bit 1 of PORTB. No effect on 400/800/1200XL. Don't
; touch any other bits in PORTB!
lda PORTB
ora #$02
sta PORTB
;3. Write some data to $A000, read it back (do twice with 2 different values)
;4. If we couldn't read back what we wrote, that means there really is a
; cartridge plugged in. Go to step 8.
lda #$AA
sta $A000
cmp $A000
bne rom_present
lsr
sta $A000
cmp $A000
bne rom_present
;5. Set RAMTOP to $C0.
lda #$c0
sta RAMTOP
;6. Do a GRAPHICS 0.
;7. Exit via RTS, so the rest of the game will load.
ramtop_ok:
jmp gr_0
;8. Do a GRAPHICS 0.
rom_present:
jsr gr_0
;9. Print a "remove cartridge" message
lda #<msg
sta FR0
lda #>msg
sta FR0+1
ldy #msglen
msgloop:
lda (FR0),y
sta (SAVMSC),y
dey
bpl msgloop
;10. Wait for a keypress
sty CH ; y == $ff at this point, clear keyboard
; ...wait for a keystroke...
wait4key:
cpy CH
beq wait4key
sty CH ; clear the key so DOS menu won't see it.
;11. Exit to DOS (without loading the rest of the file)
jmp (DOSVEC)
gr_0:
ldx #6*$10 ; CLOSE #6
lda #CLOSE
sta ICCOM,x
jsr CIOV
; GRAPHICS 0
ldx #6*$10 ; IOCB #6
lda #OPEN
sta ICCOM,x
lda #$1c ; $c = read/write
sta ICAX1,x
lda #0 ; aux2 byte zero
sta ICAX2,x
lda #<S
sta ICBAL,x
lda #>S
sta ICBAH,x
jmp CIOV
end:
.word INITAD
.word INITAD+1
.word init
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