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 no IRQs but just checks the Fifo Full/Empty bits to see when it needs to copy more data.
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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 pcmplay1.asm -o pcmplay1.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 of 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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lda #21
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sta VERA_AUDIO_RATE ; start playing
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play_loop:
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_wait_for_empty_fifo:
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bit VERA_AUDIO_CTRL ; fifo empty?
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bvc _wait_for_empty_fifo
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; fifo is empty, we go ahead and fill it with more sound data.
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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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_copy_samples:
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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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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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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 _continue
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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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_continue:
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bit VERA_AUDIO_CTRL ; is fifo full?
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bpl _copy_samples ; no, continue copying
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lda #$00
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sta VERA_DATA0 ; back to other screen color
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jmp play_loop
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_end_reached:
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; reset sound to beginning
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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 _continue
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stop_playback:
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; stop playback
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stz VERA_AUDIO_RATE
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stz VERA_AUDIO_CTRL
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ldx #<audio_off_txt
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ldy #>audio_off_txt
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jsr print
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rts
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audio_on_txt: .text "AUDIO ON", $0d, $00
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audio_off_txt: .text "AUDIO OFF", $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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