mirror of
https://github.com/sehugg/8bitworkshop.git
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248 lines
5.4 KiB
Plaintext
248 lines
5.4 KiB
Plaintext
processor 6502
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include "vcs.h"
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include "macro.h"
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include "xmacro.h"
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org $f000
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; This program demonstrates a VCS music player based on tracks
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; and patterns. A pattern is a list of variable-length notes,
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; each of which is defined by a pitch and duration.
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; There are two tracks, one for each audio channel.
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; Each track consists of a list of patterns, each entry being
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; a byte offset into the Patterns array.
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; The patterns in the tracks are played in-order until one ends,
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; and then both tracks are restarted. It's up to the composer
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; to make sure the durations in each track line up properly.
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; Patterns consist of NOTE or TONE commands. TONE sets the
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; tone of the channel (the AUDCx register) and NOTE plays a note
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; with a duration taken from a lookup table.
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; TONE 0 ends a pattern.
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; Both channels share the same logical array for tracks and patterns,
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; so both tracks can take up to 255 bytes total, and all patterns
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; can use up to 255 bytes total.
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; The music player uses 8 bytes of RAM (not counting stack).
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Trk0idx equ $e0 ; offset into tracks for channel 0
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Trk1idx equ $e1 ; offset into tracks for channel 1
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Pat0idx equ $e2 ; offset into patterns for channel 0
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Pat1idx equ $e3 ; offset into patterns for channel 1
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Chan0dur equ $e4 ; current note duration channel 0
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Chan1dur equ $e5 ; current note duration channel 1
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Chan0note equ $e6 ; current note pitch channel 0
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Chan1note equ $e7 ; current note pitch channel 1
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; Usage: NOTE pitch duration
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; Plays a note in a pattern.
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; pitch = 0-31
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; duration = 1-7, uses DurFrames lookup table
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MAC NOTE
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.pitch SET {1}
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.durat SET {2}
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.byte (.pitch+(.durat<<5))
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ENDM
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; Usage: TONE tone
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; Changes the tone in a pattern.
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; tone = 1-15
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MAC TONE
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.tone SET {1}
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.byte .tone
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ENDM
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; Usage: PATTERN address
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; Plays a pattern in a track.
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MAC PATTERN
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.addr SET {1}
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.byte (.addr-Patterns)
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ENDM
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; Usage: ENDTRACK
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; Marks the end of a track.
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MAC ENDTRACK
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.byte 0
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ENDM
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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Start
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CLEAN_START
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jsr ResetTrack
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NextFrame
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VERTICAL_SYNC
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TIMER_SETUP 37
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ldx #0
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jsr MusicFrame
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ldx #1
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jsr MusicFrame
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TIMER_WAIT
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TIMER_SETUP 192
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TIMER_WAIT
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TIMER_SETUP 30
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TIMER_WAIT
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jmp NextFrame
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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ResetTrack
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lda #0
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sta Trk0idx
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sta Pat0idx
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sta Pat1idx
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sta Chan0dur
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sta Chan1dur
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lda #Track1-Track0
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sta Trk1idx
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NextPattern
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ldy Trk0idx,x
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lda Track0,y
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beq ResetTrack
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sta Pat0idx,x
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inc Trk0idx,x
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MusicFrame
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dec Chan0dur,x ; decrement note duration
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bpl PlayNote ; only load if duration < 0
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TryAgain
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ldy Pat0idx,x ; load index into pattern table
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lda Patterns,y ; load pattern code
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beq NextPattern ; end of pattern?
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inc Pat0idx,x ; increment pattern index for next time
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pha ; save A for later
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clc ; clear carry for ROL
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rol
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rol
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rol
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rol ; rotate A left by 4 (same as ROR by 5)
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and #7 ; only take top 3 bits
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beq NoteTone ; duration zero? tone instruction
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tay ; Y = duration
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lda DurFrames,y ; look up in duration table
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sta Chan0dur,x ; save note duration
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pla ; pop saved value into A
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and #$1f ; extract first 5 bits
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sta Chan0note,x ; store as note value
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PlayNote
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lda Chan0note,x ; get note pitch for channel
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sta AUDF0,x ; store frequency register
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lda Chan0dur,x ; get note duration remaining
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clc
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ror ; divide by 2
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cmp #16
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bcc NoHighVol
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lda #15 ; make sure no greater than 15 (max)
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NoHighVol
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sta AUDV0,x ; store volume register
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rts
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; This routine is called for duration 0 (TONE) codes
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NoteTone
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pla
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and #$f
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beq NextPattern
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sta AUDC0,x
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jmp TryAgain
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Patterns
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TONE 0 ; byte 0 of patterns array is unused
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Pattern00
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TONE 3
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NOTE 16,4
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NOTE 2,4
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NOTE 16,4
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NOTE 30,4
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NOTE 16,4
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NOTE 4,4
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NOTE 30,4
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NOTE 16,4
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TONE 0
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Pattern10
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TONE 6
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NOTE 6,4
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TONE 12
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NOTE 16,4
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NOTE 18,4
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NOTE 19,4
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NOTE 22,4
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NOTE 23,4
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NOTE 26,4
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NOTE 23,4
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NOTE 26,4
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NOTE 23,4
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NOTE 26,4
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NOTE 23,4
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NOTE 22,6
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TONE 0
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Pattern11
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TONE 6
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NOTE 6,6
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NOTE 6,4
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TONE 12
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NOTE 16,4
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NOTE 18,4
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NOTE 19,4
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NOTE 22,4
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NOTE 23,4
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NOTE 26,4
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NOTE 23,4
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NOTE 26,4
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NOTE 26,4
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NOTE 22,7
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TONE 11
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NOTE 0,7
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NOTE 0,2
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TONE 0
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Pattern12
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TONE 11
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NOTE 0,5
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TONE 12
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NOTE 18,5
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NOTE 18,3
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NOTE 18,5
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NOTE 16,6
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NOTE 19,5
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NOTE 22,3
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TONE 6
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NOTE 4,5
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NOTE 4,4
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TONE 12
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NOTE 11,5
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NOTE 11,3
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NOTE 11,5
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NOTE 10,6
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NOTE 10,4
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NOTE 17,3
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NOTE 17,5
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NOTE 16,5
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TONE 0
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Track0
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PATTERN Pattern00
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PATTERN Pattern00
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PATTERN Pattern00
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PATTERN Pattern00
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PATTERN Pattern00
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PATTERN Pattern00
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PATTERN Pattern12
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ENDTRACK
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Track1
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PATTERN Pattern10
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PATTERN Pattern11
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PATTERN Pattern10
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PATTERN Pattern12
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ENDTRACK
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DurFrames
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.byte 0,4,8,12,16,24,32,48
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; Epilogue
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org $fffc
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.word Start
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.word Start
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