Ophis/examples/hello_nes/hello_prg.oph

163 lines
2.2 KiB
Plaintext
Raw Normal View History

;; PRG-ROM for our NES demo program.
.alias sprites $200 ; Keep our OAM DMA here.
.data
.org $0000
.space count 1
.space palette 32
.text
.org $C000
reset: sei
cld
; Wait two VBLANKs.
* lda $2002
bpl -
* lda $2002
bpl -
; Disable all graphics.
lda #$00
sta $2000
sta $2001
; Mask out sound IRQs.
lda #$40
sta $4017
; Clear out RAM.
lda #$00
ldx #$00
* sta $000,x
sta $100,x
sta $200,x
sta $300,x
sta $400,x
sta $500,x
sta $600,x
sta $700,x
inx
bne -
; Reset the stack pointer.
ldx #$FF
txs
; Clear the name tables.
lda #$24
sta $2006
ldy #$00
sty $2006
ldx #$08
lda #0
ldy #0
* sta $2007
iny
bne -
dex
bne -
; Load the palette from later on in the ROM.
lda #$3F
ldx #$00
sta $2006
stx $2006
* lda palette'rom,x
sta palette,x
sta $2007
inx
cpx #$20
bne -
; Load the proper sprite data into place.
ldx #$00
* lda graphics,x
sta sprites,x
inx
bne -
lda #$1E
sta count ; Update twice a second
; Un-scroll everything, just to be safe.
lda #$00
sta $2006
sta $2006
sta $2005
sta $2005
; Re-enable the displays.
lda #$80
sta $2000
lda #$1E
sta $2001
; FINALLY. We've set up the system. From here on it's all up to
; the NMI interrupt to handle things.
cli
* jmp -
vblank: ; Refresh the SPR-RAM.
lda #$02
sta $4014
; Time to update the palette?
dec count
bne irq ; If not, done.
lda #$1E
sta count ; Update twice a second
; Update those parts of the palette that aren't transparent.
ldx #$11
* txa
and #$03
beq + ; Don't update transparents
jsr bump'palette
* inx
cpx #$20
bne --
; Now re-blast that palette to VRAM.
lda #$3F
ldx #$00
sta $2006
stx $2006
* lda palette,x
sta $2007
inx
cpx #$20
bne -
; And reset the name tables.
lda #$00
sta $2006
sta $2006
sta $2005
sta $2005
irq: rti
bump'palette:
inc palette,x
lda palette,x
and #$0F
sec
sbc #$0D
bpl bump'palette
rts
palette'rom:
.byte $0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d
.byte $0d,$01,$02,$03,$0d,$04,$05,$06,$0d,$07,$08,$09,$0d,$0a,$0b,$0c
graphics:
.byte $70,$01,$00,$6c,$70,$02,$00,$74,$70,$03,$00,$7c,$70,$04,$01,$84
.byte $70,$05,$01,$8c
.byte $78,$06,$01,$6c,$78,$07,$02,$74,$78,$08,$02,$7c,$78,$03,$02,$84
.byte $78,$09,$03,$8c
.advance $FFFA
.word vblank, reset, irq