prog8/examples/cx16/pcmaudio/pcmplay2.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 the AFLOW IRQ that signals when the Fifo is about to drain empty.
; The flashing green bar is when the routine is busy copying sample data into the fifo.
;
; source code is for 64TASS, assemble with: 64tass pcmplay2.asm -o pcmplay2.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 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
; set interrupt handler
sei
ldx #<irq_handler
ldy #>irq_handler
stx IRQ_VECTOR
sty IRQ_VECTOR+1
lda #%00001000 ; enable the AFLOW irq
sta VERA_IEN
cli
lda #21
sta VERA_AUDIO_RATE ; start playback
_wait:
wai
bra _wait
irq_handler:
lda VERA_ISR
and #%00001000 ; is aflow?
bne _aflow_irq
; TODO other irq
bra _exit_irq
_aflow_irq:
; 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
; refill fifo buffer (minimum 1Kb = 1/4)
; this assumes all samples are aligned to page size!
; so we can at least copy a full page at once here.
ldx #8 ; number of pages to copy
_copy_more_pages:
ldy #0
_c1: lda (pcm_ptr),y
sta VERA_AUDIO_DATA ; lsb
iny
lda (pcm_ptr),y
sta VERA_AUDIO_DATA ; msb
iny
; (in case of 16 bit stereo output, this can be unrolled by 2 bytes again).
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 _not_at_end
bne _end_reached
; lda pcm_ptr ; uncomment if lsb also needs to be checked
; cmp #<pcm_data_end
; bcs _end_reached
_not_at_end:
; note: filling the fifo until the Fifo Full bit is set doesn't seem to work reliably
; so we just fill it with a fixed number of samples.
; in this case 8 pages = 2Kb which fills the fifo back up to 50%-75%.
dex
bne _copy_more_pages
lda #$00
sta VERA_DATA0 ; back to other screen color
_exit_irq:
ply
plx
pla
rti
_end_reached:
lda #<pcm_data
sta pcm_ptr
lda #>pcm_data
sta pcm_ptr+1
bra _not_at_end
audio_on_txt: .text "AUDIO ON (IRQ)", $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: