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shortesgap.asm
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shortesgap.asm
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;-----------------------------------------------------------------------
;
; ShortesGap
; (c) 2023 GienekP
;
;-----------------------------------------------------------------------
TMP = $00
;-----------------------------------------------------------------------
DMACTLS = $022F
IRQEN = $D20E
IRQST = $D20E
PORTB = $D301
DMACTL = $D400
NMIEN = $D40E
;-----------------------------------------------------------------------
ORG $0600
;-----------------------------------------------------------------------
INIT lda TMP
pha
lda TMP+1
pha
;-----------------------------------------------------------------------
; IRQ DISABLE
IRQDIS sei
lda #$00
sta DMACTL
sta NMIEN
sta IRQEN
sta IRQST
;-----------------------------------------------------------------------
; COPY ROM TO RAM
ROM2RAM lda PORTB
pha
lda #$C0
sta TMP+1
ldy #$00
sty TMP
ldx #$FF
CPOS stx PORTB
lda (TMP),Y
dex
stx PORTB
sta (TMP),Y
inx
iny
bne CPOS
inc TMP+1
lda TMP+1
cmp #$D0
bne OSOK
lda #$D8
sta TMP+1
OSOK cmp #$00
bne CPOS
pla
and #$FE
sta PORTB
;-----------------------------------------------------------------------
; IRQ ENABLE
IRQENB lda #$40
sta NMIEN
lda #$F7
sta IRQST
lda DMACTLS
sta DMACTL
cli
;-----------------------------------------------------------------------
; RESTORE TMP
pla
sta TMP+1
pla
sta TMP
;-----------------------------------------------------------------------
; UPGRADE
UPGRADE ldx #$04 ; $04
stx $BFD4 ; Dolarnik
dex ; $03
dex ; $02
dex ; $01
stx $EE17 ; Short Gap for NTSC
stx $EE18 ; Short Gap for PAL
dex ; $00
stx $BC42 ; No cursor
rts
;-----------------------------------------------------------------------
nop
nop
;-----------------------------------------------------------------------
INI INIT
;-----------------------------------------------------------------------