prog8/examples/cx16/pcmaudio/pcmplay1.asm

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2022-11-26 14:53:35 +00:00
;
; This program plays a short mono 16 bit PCM sample on repeat
; It uses no IRQs but just checks the Fifo Full/Empty bits to see when it needs to copy more data.
; The flashing green bar is when the routine is busy copying sample data into the fifo.
;
; source code is for 64TASS, assemble with: 64tass pcmplay1.asm -o pcmplay1.prg
;
.cpu 'w65c02'
.enc 'none'
* = $0801
; basic launcher
.word $080b, 2022
.text $9e, "2061", $00
.word 0
entrypoint:
CHROUT = $ffd2
VERA_ADDR_L = $9f20
VERA_ADDR_M = $9f21
VERA_ADDR_H = $9f22
VERA_DATA0 = $9f23
VERA_CTRL = $9f25
VERA_IEN = $9f26
VERA_ISR = $9f27
VERA_AUDIO_CTRL = $9f3b
VERA_AUDIO_RATE = $9f3c
VERA_AUDIO_DATA = $9f3d
IRQ_VECTOR = $0314
r0 = $02
r0L = $02
r0H = $03
r1 = $04
r1L = $04
r1H = $05
pcm_ptr = $06
; stop playback and select mono 16 bit, max volume
stz VERA_AUDIO_RATE
lda #%10101111
sta VERA_AUDIO_CTRL
; fill the fifo with some of silence
ldy #1024/256
_z1: ldx #0
_z2: stz VERA_AUDIO_DATA
dex
bne _z2
dey
bne _z1
ldx #<audio_on_txt
ldy #>audio_on_txt
jsr print
ldx #<pcm_data
ldy #>pcm_data
stx pcm_ptr
sty pcm_ptr+1
lda #21
sta VERA_AUDIO_RATE ; start playing
play_loop:
_wait_for_empty_fifo:
bit VERA_AUDIO_CTRL ; fifo empty?
bvc _wait_for_empty_fifo
; fifo is empty, we go ahead and fill it with more sound data.
; paint a screen color
stz VERA_CTRL
lda #$0c
sta VERA_ADDR_L
lda #$fa
sta VERA_ADDR_M
lda #$01
sta VERA_ADDR_H
lda #$a0
sta VERA_DATA0
_copy_samples:
; this assumes all samples are aligned to page size!
; so we can at least copy a full page at once here.
ldy #0
_c1 lda (pcm_ptr),y
sta VERA_AUDIO_DATA ; lsb
iny
lda (pcm_ptr),y
sta VERA_AUDIO_DATA ; msb
iny
bne _c1
inc pcm_ptr+1
; have we reached the end of the sample data? (pcm_ptr >= pcm_data_end)
; due to page size alignment only the MSB has to be checked
lda pcm_ptr+1
cmp #>pcm_data_end
bcc _continue
bne _end_reached
; lda pcm_ptr ; uncomment if lsb also needs to be checked
; cmp #<pcm_data_end
; bcs _end_reached
_continue:
bit VERA_AUDIO_CTRL ; is fifo full?
bpl _copy_samples ; no, continue copying
lda #$00
sta VERA_DATA0 ; back to other screen color
jmp play_loop
_end_reached:
; reset sound to beginning
lda #<pcm_data
sta pcm_ptr
lda #>pcm_data
sta pcm_ptr+1
bra _continue
stop_playback:
; stop playback
stz VERA_AUDIO_RATE
stz VERA_AUDIO_CTRL
ldx #<audio_off_txt
ldy #>audio_off_txt
jsr print
rts
audio_on_txt: .text "AUDIO ON", $0d, $00
audio_off_txt: .text "AUDIO OFF", $0d, $00
print: ; -- print string pointed to by X/Y
stx r0L
sty r0H
ldy #0
_chr: lda (r0),y
beq _done
jsr $ffd2
iny
bne _chr
_done: rts
.align $0100
pcm_data:
.binary "small-pcm-mono.bin"
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pcm_data_end: