mirror of
https://github.com/michaelcmartin/Ophis.git
synced 2024-12-22 03:29:55 +00:00
163 lines
2.2 KiB
Plaintext
163 lines
2.2 KiB
Plaintext
;; PRG-ROM for our NES demo program.
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.alias sprites $200 ; Keep our OAM DMA here.
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.data
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.org $0000
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.space count 1
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.space palette 32
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.text
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.org $C000
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reset: sei
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cld
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; Wait two VBLANKs.
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* lda $2002
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bpl -
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* lda $2002
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bpl -
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; Disable all graphics.
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lda #$00
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sta $2000
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sta $2001
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; Mask out sound IRQs.
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lda #$40
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sta $4017
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; Clear out RAM.
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lda #$00
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ldx #$00
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* sta $000,x
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sta $100,x
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sta $200,x
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sta $300,x
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sta $400,x
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sta $500,x
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sta $600,x
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sta $700,x
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inx
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bne -
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; Reset the stack pointer.
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ldx #$FF
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txs
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; Clear the name tables.
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lda #$24
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sta $2006
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ldy #$00
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sty $2006
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ldx #$08
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lda #0
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ldy #0
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* sta $2007
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iny
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bne -
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dex
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bne -
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; Load the palette from later on in the ROM.
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lda #$3F
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ldx #$00
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sta $2006
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stx $2006
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* lda palette'rom,x
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sta palette,x
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sta $2007
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inx
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cpx #$20
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bne -
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; Load the proper sprite data into place.
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ldx #$00
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* lda graphics,x
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sta sprites,x
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inx
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bne -
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lda #$1E
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sta count ; Update twice a second
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; Un-scroll everything, just to be safe.
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lda #$00
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sta $2006
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sta $2006
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sta $2005
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sta $2005
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; Re-enable the displays.
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lda #$80
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sta $2000
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lda #$1E
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sta $2001
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; FINALLY. We've set up the system. From here on it's all up to
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; the NMI interrupt to handle things.
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cli
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* jmp -
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vblank: ; Refresh the SPR-RAM.
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lda #$02
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sta $4014
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; Time to update the palette?
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dec count
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bne irq ; If not, done.
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lda #$1E
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sta count ; Update twice a second
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; Update those parts of the palette that aren't transparent.
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ldx #$11
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* txa
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and #$03
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beq + ; Don't update transparents
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jsr bump'palette
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* inx
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cpx #$20
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bne --
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; Now re-blast that palette to VRAM.
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lda #$3F
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ldx #$00
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sta $2006
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stx $2006
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* lda palette,x
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sta $2007
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inx
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cpx #$20
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bne -
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; And reset the name tables.
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lda #$00
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sta $2006
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sta $2006
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sta $2005
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sta $2005
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irq: rti
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bump'palette:
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inc palette,x
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lda palette,x
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and #$0F
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sec
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sbc #$0D
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bpl bump'palette
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rts
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palette'rom:
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.byte $0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d,$0d
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.byte $0d,$01,$02,$03,$0d,$04,$05,$06,$0d,$07,$08,$09,$0d,$0a,$0b,$0c
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graphics:
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.byte $70,$01,$00,$6c,$70,$02,$00,$74,$70,$03,$00,$7c,$70,$04,$01,$84
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.byte $70,$05,$01,$8c
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.byte $78,$06,$01,$6c,$78,$07,$02,$74,$78,$08,$02,$7c,$78,$03,$02,$84
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.byte $78,$09,$03,$8c
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.advance $FFFA
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.word vblank, reset, irq
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