2022-11-26 14:53:35 +00:00
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;
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; This program plays a short mono 16 bit PCM sample on repeat
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; It uses the AFLOW IRQ that signals when the Fifo is about to drain empty.
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; The flashing green bar is when the routine is busy copying sample data into the fifo.
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;
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; source code is for 64TASS, assemble with: 64tass pcmplay2.asm -o pcmplay2.prg
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;
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.cpu 'w65c02'
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.enc 'none'
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* = $0801
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; basic launcher
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.word $080b, 2022
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.text $9e, "2061", $00
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.word 0
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entrypoint:
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CHROUT = $ffd2
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VERA_ADDR_L = $9f20
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VERA_ADDR_M = $9f21
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VERA_ADDR_H = $9f22
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VERA_DATA0 = $9f23
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VERA_CTRL = $9f25
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VERA_IEN = $9f26
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VERA_ISR = $9f27
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VERA_AUDIO_CTRL = $9f3b
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VERA_AUDIO_RATE = $9f3c
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VERA_AUDIO_DATA = $9f3d
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IRQ_VECTOR = $0314
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r0 = $02
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r0L = $02
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r0H = $03
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r1 = $04
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r1L = $04
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r1H = $05
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pcm_ptr = $06
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; stop playback and select mono 16 bit, max volume
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stz VERA_AUDIO_RATE
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lda #%10101111
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sta VERA_AUDIO_CTRL
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; fill the fifo with some silence
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ldy #1024/256
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_z1: ldx #0
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_z2: stz VERA_AUDIO_DATA
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dex
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bne _z2
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dey
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bne _z1
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ldx #<audio_on_txt
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ldy #>audio_on_txt
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jsr print
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ldx #<pcm_data
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ldy #>pcm_data
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stx pcm_ptr
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sty pcm_ptr+1
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; set interrupt handler
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sei
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ldx #<irq_handler
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ldy #>irq_handler
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stx IRQ_VECTOR
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sty IRQ_VECTOR+1
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lda #%00001000 ; enable the AFLOW irq
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sta VERA_IEN
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cli
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lda #21
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sta VERA_AUDIO_RATE ; start playback
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_wait:
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wai
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bra _wait
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irq_handler:
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lda VERA_ISR
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and #%00001000 ; is aflow?
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bne _aflow_irq
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; TODO other irq
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bra _exit_irq
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_aflow_irq:
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; paint a screen color
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stz VERA_CTRL
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lda #$0c
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sta VERA_ADDR_L
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lda #$fa
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sta VERA_ADDR_M
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lda #$01
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sta VERA_ADDR_H
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lda #$a0
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sta VERA_DATA0
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; refill fifo buffer (minimum 1Kb = 1/4)
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; this assumes all samples are aligned to page size!
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; so we can at least copy a full page at once here.
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ldx #8 ; number of pages to copy
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_copy_more_pages:
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ldy #0
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_c1: lda (pcm_ptr),y
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sta VERA_AUDIO_DATA ; lsb
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iny
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lda (pcm_ptr),y
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sta VERA_AUDIO_DATA ; msb
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iny
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; (in case of 16 bit stereo output, this can be unrolled by 2 bytes again).
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bne _c1
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inc pcm_ptr+1
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; have we reached the end of the sample data? (pcm_ptr >= pcm_data_end)
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; due to page size alignment only the MSB has to be checked
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lda pcm_ptr+1
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cmp #>pcm_data_end
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bcc _not_at_end
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bne _end_reached
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; lda pcm_ptr ; uncomment if lsb also needs to be checked
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; cmp #<pcm_data_end
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; bcs _end_reached
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_not_at_end:
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; note: filling the fifo until the Fifo Full bit is set doesn't seem to work reliably
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; so we just fill it with a fixed number of samples.
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; in this case 8 pages = 2Kb which fills the fifo back up to 50%-75%.
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dex
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bne _copy_more_pages
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lda #$00
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sta VERA_DATA0 ; back to other screen color
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_exit_irq:
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ply
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plx
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pla
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rti
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_end_reached:
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lda #<pcm_data
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sta pcm_ptr
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lda #>pcm_data
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sta pcm_ptr+1
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bra _not_at_end
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audio_on_txt: .text "AUDIO ON (IRQ)", $0d, $00
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print: ; -- print string pointed to by X/Y
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stx r0L
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sty r0H
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ldy #0
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_chr: lda (r0),y
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beq _done
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jsr $ffd2
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iny
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bne _chr
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_done: rts
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.align $0100
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pcm_data:
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2023-03-02 23:47:12 +00:00
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.binary "small-pcm-mono.bin"
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2022-11-26 14:53:35 +00:00
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pcm_data_end:
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