dos33fsprogs/music/tiny_tracker5/play_frame.s

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2022-01-19 04:53:24 +00:00
play_frame:
;============================
; see if still counting down
lda SONG_COUNTDOWN
bpl done_update_song
set_notes_loop:
;==================
; load next byte
ldy SONG_OFFSET
lda tracker_song,Y
;==================
; see if hit end
; this song only 16 notes so valid notes always positive
; cmp #$80
bpl not_end
;====================================
; if at end, loop back to beginning
asl ; reset song offset to 0
sta SONG_OFFSET
beq set_notes_loop
not_end:
; NNNNNECC -- c=channel, e=end, n=note
pha ; save note
and #3
tax
ldy #$0E
sty AY_REGS+8,X ; $08 set volume A,B,C
asl
tax ; put channel offset in X
pla ; restore note
tay
and #$4
sta SONG_COUNTDOWN ; always 4 long?
tya
lsr
lsr
lsr ; get note in A
tay ; lookup in table
lda frequencies_high,Y
sta AY_REGS+1,X
; sta $500,X
lda frequencies_low,Y
sta AY_REGS,X ; set proper register value
; visualization
blah_urgh:
sta $400,Y
inc blah_urgh+1
;============================
; point to next
; assume less than 256 bytes
inc SONG_OFFSET
done_update_song:
dec SONG_COUNTDOWN
bmi set_notes_loop