dos33fsprogs/music/tiny_tracker4/play_frame.s
2022-01-15 15:41:53 -05:00

82 lines
1016 B
ArmAsm

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
cmp #$FF
bne all_ok
;====================================
; if at end, loop back to beginning
lda #0 ; reset song offset
sta SONG_OFFSET
beq set_notes_loop ; bra
all_ok:
note_only:
; NNNNNECC -- c=channel, e=end, n=note
tay ; save note in Y
and #3
asl
tax ; put channel offset in X
tya
and #$4
sta SONG_COUNTDOWN ; always 4 long?
tya
lsr
lsr
lsr ; get note in A
tay ; lookup in table
lda frequencies_low,Y
sta AY_REGS,X ; set proper register value
lda frequencies_high,Y
sta AY_REGS+1,X
;============================
; point to next
; assume less than 256 bytes
inc SONG_OFFSET
lda SONG_COUNTDOWN
beq set_notes_loop ; bra
.include "ay3_write_regs.s"
done_update_song:
dec SONG_COUNTDOWN