mirror of https://github.com/safiire/n65.git
183 lines
3.5 KiB
NASM
183 lines
3.5 KiB
NASM
.ines {"prog": 1, "char": 0, "mapper": 0, "mirror": 0}
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.inc <nes.sym>
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.segment prog 0
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;; SRAM Variables
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.org $0000
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.scope audio
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.space timer 1
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.space next_note 1
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.space note_frequency 2
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.
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;; Interrupt vectors
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.org $FFFA
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.dw vblank
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.dw main
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.dw irq
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.org $C000
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.scope main
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sei
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cld
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;; Setup the stack
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ldx #$ff
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txs
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;; Disable rendering, reset APU
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ldx #$00
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stx nes.ppu.control
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stx nes.ppu.mask
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jsr zero_apu
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.scope
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wait_vblank:
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bit nes.ppu.status
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bpl wait_vblank
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.
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clear_ram:
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lda #$00
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sta $00, x
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sta $100, 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 $700, x
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lda #$ff
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sta $200, x
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inx
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bne clear_ram
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.scope
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wait_vblank:
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bit nes.ppu.status
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bpl wait_vblank
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.
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jsr initialize
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forever:
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jmp forever
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rti
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.
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;; Zero the APU
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.scope zero_apu
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lda #$00
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ldx #$00
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loop:
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sta $4000, x
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inx
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cpx $18
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bne loop
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rts
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.
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;; Initialize PPU and APU
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.scope initialize
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lda #%00000011
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sta nes.apu.channel_enable
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; Reenable interrupts, Turn Vblank back on
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lda #%10000000
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sta nes.ppu.control
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; Initialize the audio structure
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lda #$00
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sta audio.timer zp
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lda #$30
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sta audio.next_note zp
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cli
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rts
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.
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;; Keep time via 60fps vblank
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.scope vblank
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; Update the audio timer so it resets every 64 frames
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ldx audio.timer zp
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inx
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txa
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and #%00000011
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sta audio.timer zp
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bne return
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; Play the next note on reset
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lda audio.next_note zp
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cmp #$80
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bmi continue
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lda #$30
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continue:
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jsr play_note
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sta audio.next_note zp
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inc audio.next_note zp
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return:
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rti
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.
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;; Hi and lo byte tables for note frequencies
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.scope midi_notes
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.scope hi
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.bytes $35, $32, $2f, $2c, $2a, $28, $25, $23, $21, $1f, $1d, $1c, $1a, $19, $17, $16
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.bytes $15, $14, $12, $11, $10, $0f, $0e, $0e, $0d, $0c, $0b, $0b, $0a, $0a, $09, $08
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.bytes $08, $07, $07, $07, $06, $06, $05, $05, $05, $05, $04, $04, $04, $03, $03, $03
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.bytes $03, $03, $02, $02, $02, $02, $02, $02, $02, $01, $01, $01, $01, $01, $01, $01
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.bytes $01, $01, $01, $01, $01, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00
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.bytes $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00
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.bytes $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00
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.bytes $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00
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.
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.scope lo
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.bytes $71, $71, $9c, $f0, $6a, $09, $ca, $ab, $aa, $c6, $fe, $4f, $b8, $38, $ce, $78
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.bytes $35, $04, $e4, $d5, $d5, $e3, $fe, $27, $5b, $9c, $e6, $3b, $9a, $01, $72, $ea
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.bytes $6a, $f1, $7f, $13, $ad, $4d, $f3, $9d, $4c, $00, $b8, $74, $34, $f8, $bf, $89
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.bytes $56, $26, $f9, $ce, $a6, $80, $5c, $3a, $1a, $fb, $df, $c4, $ab, $93, $7c, $67
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.bytes $52, $3f, $2d, $1c, $0c, $fd, $ef, $e1, $d5, $c9, $bd, $b3, $a9, $9f, $96, $8e
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.bytes $86, $7e, $77, $70, $6a, $64, $5e, $59, $54, $4f, $4b, $46, $42, $3f, $3b, $38
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.bytes $34, $31, $2f, $2c, $29, $27, $25, $23, $21, $1f, $1d, $1b, $1a, $18, $17, $15
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.bytes $14, $13, $12, $11, $10, $0f, $0e, $0d, $0c, $0c, $0b, $0a, $0a, $09, $08, $08
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.
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.
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;; Play midi note held in A
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.scope play_note
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pha
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tax
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lda #%10011111
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sta nes.apu.pulse1.control
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; Get the low byte of the timer
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ldy midi_notes.lo, x
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sty nes.apu.pulse1.ft
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sty audio.note_frequency+1 zp
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; Get the high 3 bits of the timer
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ldy midi_notes.hi, x
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tya
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and #%00000111
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ora #%11111000
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sta nes.apu.pulse1.ct
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sta audio.note_frequency zp
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pla
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rts
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.
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;; IRQ, we are not using
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.scope irq
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rti
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.
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