mirror of https://github.com/safiire/n65.git
202 lines
3.5 KiB
NASM
202 lines
3.5 KiB
NASM
;------------------------------------------------------------------------------
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; An NES music engine that understands the binary stream outputted from my
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; MIDI converter :)
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;;;;
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; Create an iNES header
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.ines {"prog": 1, "char": 0, "mapper": 0, "mirror": 0}
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;;;;
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; Include all the symbols in the nes library
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.inc <nes.sym>
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;;;;
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; Let's put a data structure to control the sound engine in the zero page
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.org $0000
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.scope sound_engine
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; Where we are reading from ROM
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.space stream_read_ptr_lo 1
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.space stream_read_ptr_hi 1
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; Where we are writing in the APU
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.space stream_write_ptr_lo 1
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.space stream_write_ptr_hi 1
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.space delta 1
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.
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;;;;
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; Open the prog section bank 0
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.segment prog 0
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;;;;
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; Setup the 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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;;;;
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; Here is our code entry point, which we'll call main.
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.org $C000
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.scope main
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; Disable interrupts and decimal flag
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sei
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cld
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; Wait for 2 vblanks
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wait_vb1:
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lda nes.ppu.status
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bpl wait_vb1
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wait_vb2:
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lda nes.ppu.status
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bpl wait_vb2
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; Now we want to initialize the hardware to a known state
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lda #%00
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ldx #$00
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clear_segments:
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sta $0, 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 $700, x
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inx
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bne clear_segments
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; Reset the stack pointer
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ldx #$FF
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txs
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; Disable all graphics and vblank nmi
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lda #$00
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sta nes.ppu.control
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sta nes.ppu.mask
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; Initialize sound engine structure
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; To read from $D000, and to write to $40**
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lda #>music_buffer
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sta sound_engine.stream_read_ptr_hi
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lda #<music_buffer
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sta sound_engine.stream_read_ptr_lo
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; Make the first delta happen immediately
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lda #$01
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sta sound_engine.delta
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lda #$40
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sta sound_engine.stream_write_ptr_hi
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jsr init_sound
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; Resume interrupts and NMI and loop here forever
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lda #%10000000
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sta nes.ppu.control
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cli
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forever:
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jmp forever
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.
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;;;;
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; Initialize the APU to enable Pulse1
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; Bitfield: ---D NT21
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.scope init_sound
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lda #$00
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sta nes.apu.pulse1.control
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sta nes.apu.pulse1.ramp_control
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sta nes.apu.pulse1.ft
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sta nes.apu.pulse1.ct
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lda #$01
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sta nes.apu.channel_enable
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rts
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.
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;;;;
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; VBlank reads our music buffer
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.scope vblank
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; Backup our registers
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pha
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txa
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pha
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tya
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pha
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jsr sound_engine_driver
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; Restore the registers
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pla
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tay
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pla
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tax
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pla
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rti
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.
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;;;;
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; Sound driver that updates the APU registers
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; via a stream of APU write commands
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.scope sound_engine_driver
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dec sound_engine.delta
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bne done
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read_event:
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; Load the new delta from the stream
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ldy #$00
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lda (sound_engine.stream_read_ptr_lo), Y
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sta sound_engine.delta
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; Read pulse1 control register value
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ldy #$01
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lda (sound_engine.stream_read_ptr_lo), Y
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sta nes.apu.pulse1.control
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; Read the value for pulse1.ft
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ldy #$02
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lda (sound_engine.stream_read_ptr_lo), Y
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sta nes.apu.pulse1.ft
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; Read the value for pulse1.ct
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ldy #$03
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lda (sound_engine.stream_read_ptr_lo), Y
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sta nes.apu.pulse1.ct
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; Advance the 16-bit stream pointer by number of bytes read
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lda sound_engine.stream_read_ptr_lo
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clc
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adc #$04
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sta sound_engine.stream_read_ptr_lo
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bcc done
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inc sound_engine.stream_read_ptr_hi
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; If the very next event is 0 delta away, do it now too
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; Read the value for pulse1.ct
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ldy #$04
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lda (sound_engine.stream_read_ptr_lo), Y
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beq read_event
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done:
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rts
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.
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;;;;
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; IRQ Does nothing
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.scope irq
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rti
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.
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;;;;
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; Include the music buffer stream
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.org $D000
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music_buffer:
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.incbin "data.mus"
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