82 lines
1016 B
ArmAsm
82 lines
1016 B
ArmAsm
play_frame:
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;============================
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; see if still counting down
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lda SONG_COUNTDOWN
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bpl done_update_song
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set_notes_loop:
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;==================
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; load next byte
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ldy SONG_OFFSET
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lda tracker_song,Y
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;==================
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; see if hit end
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cmp #$FF
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bne all_ok
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;====================================
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; if at end, loop back to beginning
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lda #0 ; reset song offset
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sta SONG_OFFSET
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beq set_notes_loop ; bra
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all_ok:
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note_only:
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; NNNNNECC -- c=channel, e=end, n=note
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tay ; save note in Y
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and #3
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asl
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tax ; put channel offset in X
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tya
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and #$4
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sta SONG_COUNTDOWN ; always 4 long?
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tya
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lsr
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lsr
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lsr ; get note in A
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tay ; lookup in table
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lda frequencies_low,Y
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sta AY_REGS,X ; set proper register value
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lda frequencies_high,Y
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sta AY_REGS+1,X
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;============================
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; point to next
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; assume less than 256 bytes
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inc SONG_OFFSET
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lda SONG_COUNTDOWN
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beq set_notes_loop ; bra
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.include "ay3_write_regs.s"
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done_update_song:
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dec SONG_COUNTDOWN
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