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8bitworkshop/presets/vcs/examples/fracpitch.a

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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; Playing music on the Atari VCS can be challenging since
;; the frequencies rarely line up with the desired notes of a
;; musical scale, and if they do, they're likely out of tune.
;; There are only 32 divisors to configure pitch for a channel,
;; and three possible base clocks that produce square tones --
;; a total of 96 possible frequencies.
;;
;; This demo implements fractional frequencies by duty cycling
;; the frequency divisor.
;; This extends the number of audible pitches to 768.
;;
;; We have a lookup table with AUDF, AUDC, and a duty cycle
;; bitmask for each note. Every 2 msec, we rotate the bitmask
;; and add the next bit to the divisor -- cycling between
;; two neighboring divisors.
;;
;; The pitches are modulated 8 times per frame, but could
;; be reduced to 1 or 2 times per frame, but "vibrato"
;; would be more apparent.
;;
;; The song file format is simple:
;; - High bit set: delay (0-126)
;; - High bit clear: note (0-63)
;; - $FF: done
;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
processor 6502
include "vcs.h"
include "macro.h"
include "xmacro.h"
org $f000
Chan0dur equ $e0 ; current note duration channel 0
Chan1dur equ $e1 ; current note duration channel 1
Chan0note equ $e2 ; current note pitch channel 0
Chan1note equ $e3 ; current note pitch channel 1
Chan0duty equ $e4 ; current duty bits channel 0
Chan1duty equ $e5 ; current duty bits channel 1
DurationTimer equ $e6 ; duration until next cmd
CurChannel equ $e7 ; next channel to add note
SongPtr equ $e8 ; ptr to next song byte
BitmapY equ $f0 ; next line of bitmap
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
MAC PULSE
TIMER_SETUP 33
jsr DutyCycle ; cycle notes
jsr Pulse ; decrement duration timer
lda Chan0note
sta COLUBK
lda Chan1note
sta COLUPF
jsr DrawBitmap ; draw ~33 lines of bitmap
ENDM
MAC DUTYCYCLE
TIMER_SETUP 32
jsr DutyCycle ; cycle notes
jsr DrawBitmap ; draw ~32 lines of bitmap
ENDM
Start
CLEAN_START
jsr ResetTrack
NextFrame
VERTICAL_SYNC
lda #$d0
sta BitmapY ; top of bitmap
; 35*2 + 34*6 = 274 lines (264 b/c we exit timer early)
PULSE
DUTYCYCLE
DUTYCYCLE
DUTYCYCLE
PULSE
DUTYCYCLE
DUTYCYCLE
DUTYCYCLE
lda #0
sta COLUBK
jmp NextFrame
DrawBitmap
ldy BitmapY
ScanLoop
; WSYNC and store playfield registers
sta WSYNC
lda PFBitmap0,y
sta PF0 ; store first playfield byte
lda PFBitmap1,y
sta PF1 ; store 2nd byte
lda PFBitmap2,y
sta PF2 ; store 3rd byte
; Here's the asymmetric part -- by this time the TIA clock
; is far enough that we can rewrite the same PF registers
; and display new data on the right side of the screen
nop
nop
nop ; pause to let playfield finish drawing
lda PFBitmap3,y
sta PF0 ; store 4th byte
lda PFBitmap4,y
sta PF1 ; store 5th byte
lda PFBitmap5,y
sta PF2 ; store 6th byte
dey
lda INTIM
cmp #2
bcs ScanLoop ; repeat until all scanlines drawn
TIMER_WAIT
sty BitmapY
lda #0
sta PF0
sta PF1
sta PF2
rts
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Table of AUDF base values for each note
FREQZ .byte 30, 30, 30, 30, 30, 28, 26, 25, 23, 22, 21, 19, 18, 17, 16, 15, 14, 13, 12, 12, 11, 10, 10, 9, 8, 8, 7, 7, 6, 6, 5, 5, 30, 29, 27, 25, 24, 22, 21, 20, 19, 18, 16, 15, 15, 14, 13, 12, 11, 11, 10, 31, 29, 27, 25, 24, 23, 21, 20, 19, 18, 16, 15, 15
; Table of duty-cycle bits for each note
DUTYZ .byte 247, 247, 247, 247, 1, 73, 219, 1, 219, 73, 0, 219, 181, 85, 85, 85, 181, 219, 247, 1, 73, 181, 0, 73, 219, 17, 219, 17, 219, 73, 247, 85, 247, 1, 85, 247, 73, 247, 181, 17, 1, 0, 247, 247, 0, 1, 17, 73, 181, 0, 17, 0, 1, 85, 247, 73, 0, 181, 73, 1, 0, 247, 247, 0
; Table of AUDC values for each note
TONEZ .byte 0, 0, 0, 0, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4
; Cycle the pitches of each channel
DutyCycle
; set playfield colors
lda Chan0duty
ora #$07
sta COLUBK
lda Chan1duty
and #$f0
sta COLUPF
; update channel 0
ldx #0
jsr MusicFrame
; update channel 1
ldx #1
jsr MusicFrame
rts
; Play a note
; X = channel (0,1)
; Y = note index (0-63)
PlayNote
lda FREQZ,y
sta Chan0note,x
lda DUTYZ,y
sta Chan0duty,x
lda TONEZ,y
sta AUDC0,x
lda #31
sta Chan0dur,x
lda #15
sta AUDV0,x
rts
; Reset to start of song
ResetTrack
lda #<NOTEZ
sta SongPtr+0
lda #>NOTEZ
sta SongPtr+1
rts
; Called 2x per frame
; Decrement the volumes for each channel
; Also decrement next-note timer, fetch next note
Pulse
lda Chan0dur
beq NoDec0
lsr
sta AUDV0
dec Chan0dur
NoDec0
lda Chan1dur
beq NoDec1
lsr
sta AUDV1
dec Chan1dur
NoDec1
lda DurationTimer
beq NextData
dec DurationTimer
rts
; Timer ran out, so fetch next note
NextData
ldx #0
lda (SongPtr,x)
bmi LoadDuration
; < $80, play next note
ldx CurChannel ; next channel
tay
jsr PlayNote
inx
txa
and #1
sta CurChannel ; inc next channel
jmp IncDataPtr
; >= $80, load next duration
LoadDuration
cmp #$ff ; $ff = end of song
beq ResetTrack
and #$7f
asl
sta DurationTimer ; store duration * 2
IncDataPtr
; increment song pointer
inc SongPtr
bne NoIncHi
inc SongPtr+1
NoIncHi
rts
; Update channel pitch in AUDF0
MusicFrame
; 8-bit rotation of duty cycle bits
lda Chan0duty,x
asl
bcc NoCarry
ora #1
NoCarry
sta Chan0duty,x
lda Chan0note,x
; If next bit is set, add 1 to AUDF0
adc #0
sta AUDF0,x
VolZero
rts
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; MUSIC DATA - "The Easy Winners" by Scott Joplin
NOTEZ
hex 2a1e983327a431258c2f238c2e228c2c
hex 208c2a1e98281c8c271b9825198c2317
hex 8c22128c238c258c278c281e8c2a1c8c
hex 2c1b8c2e198c2f17981e9812981e982f
hex 17983327981298361e9838178c368c1e
hex 8c388c33128c388c361e983d108c3b8c
hex 208c378c3b108c3d8c3b288c368c1798
hex 2a1e8c2c8c2e128c2f8c311e8c328c33
hex 1798331e981298331e9838178c368c27
hex 8c388c36188c368c33219836198c2e8c
hex 228c368c2f198c368c2f25982e1e981c
hex 981b8c2a8c2e258c348c331798331e98
hex 129833279838178c368c1e8c388c3612
hex 8c388c331e983d108c3b8c208c3d8c3b
hex 1c8c3b8c381c8c3f8c1b8c338c37228c
hex 3a8c3f0f983a8c3b8c3d108c3b8c208c
hex 3d8c38108c3d8c3b288c368c178c348c
hex 361e8c348c33178c368c278c368c3012
hex 8c348c1e8c368c34128c338c281e982f
hex 1e981298149816983317983327981298
hex 331e9838178c368c1e8c388c36128c38
hex 8c331e983d108c3b8c208c3d8c3b108c
hex 3d8c38288c368c17982a1e8c2c8c2e12
hex 8c2f8c311e8c328c331798331e981298
hex 361e9838178c368c278c328c36188c36
hex 8c36219836198c2e8c228c368c35198c
hex 368c2f2598361e981c981b8c2a8c2e25
hex 8c348c2f1798331e981298361e983817
hex 8c368c1e8c328c36128c388c361e983d
hex 108c388c288c3d8c3b1c8c3b8c3d1c8c
hex 378c1b8c338c37168c3a8c3f1b983a8c
hex 3b8c3d108c3b8c208c3d8c3b108c3d8c
hex 38288c368c178c388c361e8c348c2f17
hex 8c368c278c368c36128c348c1e8c308c
hex 34128c338c311e982f179812982f0b98
hex 2a8c2b8c2c128c2d8c2e288c2e8c168c
hex 368c341e8c318c2c198c2d8c2e288c2e
hex 8c198c318c2c1a8c2e8c2f1b8c2a8c2c
hex 278c2e8c2f128c308c311e8c328c3323
hex 8c328c331e8c338c128c368c311e8c33
hex 8c34258c3d8c1e8c338c34128c3d8c1e
hex 8c338c34258c3d8c1e8c3b8c3a128c38
hex 8c36168c348c33178c3b8c278c328c33
hex 128c3b8c1e8c328c33178c3b8c278c38
hex 8c36128c338c311e8c2f8c2e148c2f8c
hex 302a8c308c188c368c33208c308c2e1b
hex 8c2f8c302a8c308c148c338c38208c33
hex 8c31198c308c31288c2c8c1c8c308c31
hex 208c348c38198c338c34208c318c258c
hex 2c8c288c258c261d8c29208c2c238c2f
hex 268c32298c322998322998358c388c32
hex 8c3eb03f8c3b8c368c338c338c2f8c27
hex 8c2a8c28128c288c128c2f8c17982a8c
hex 2b8c2c128c2d8c2e288c318c168c368c
hex 341e8c318c2c198c2d8c2e288c2e8c19
hex 8c318c2c1a8c2e8c2f1b8c2a8c2c278c
hex 2e8c2f128c308c311e8c328c33178c32
hex 8c33278c338c128c368c311e8c338c34
hex 198c3d8c288c338c34128c3d8c1e8c33
hex 8c34198c3d8c288c3b8c3a128c388c36
hex 168c348c33178c3b8c278c328c33128c
hex 3b8c1e8c328c33178c3b8c278c388c36
hex 128c338c311e8c2f8c2e148c2f8c302a
hex 8c308c188c368c33208c308c2e1b8c2f
hex 8c302a8c308c148c338c38208c338c31
hex 198c308c31288c2c8c1c8c308c31208c
hex 348c38198c338c34208c318c258c2c8c
hex 288c258c261d8c29208c2c238c2f268c
hex 32298c322998322998358c2f8c3b8c3e
hex b03f8c3b8c368c338c338c2f8c278c2a
hex 8c281e8c288c128c2f8c17982a983317
hex 98331e981298331e9838178c368c1e8c
hex 388c36128c388c3327983d108c3b8c20
hex 8c3d8c3b108c378c3b208c368c17982a
hex 1e8c2c8c2e128c2f8c311e8c328c3317
hex 983327981298361e9838178c338c278c
hex 388c36188c368c36219836198c318c22
hex 8c368c2f198c368c2f2598361e981c98
hex 1b8c2a8c2e258c348c331798331e9812
hex 9836279838178c338c1e8c388c36128c
hex 388c361e983d108c388c208c3d8c3b1c
hex 8c3b8c3d1c8c378c1b8c338c37228c3a
hex 8c3f0f983a8c3b8c37108c3b8c208c3d
hex 8c3b1c8c3d8c3b208c338c178c388c36
hex 1e8c348c2f238c368c1e8c368c36128c
hex 348c1e8c368c311e8c338c3112982f17
hex 9812982f0bb03428983428a42f238c34
hex 288c362a8c38982ca42f8c348c388c2f
hex 8c3698338c178c338c2d17982c1c9810
hex 9812982f148c308c31158c398c2d8c36
hex 8c301e8c398c1f8c368c2f208c348c38
hex 2c8c3d8c1c8c3b8c38238c348c33178c
hex 3b8c362d8c338c311e8c338c1f8c2f8c
hex 34208c348c381c8c3b8c238c3d8c3b14
hex 8c388c31158c398c258c368c302a8c39
hex 8c1f8c368c2f208c348c38238c3d8c1c
hex 8c3b8c382c8c348c36198c388c36288c
hex 348c33128c348c2e8c318c2f2398321d
hex 8c361e8c3317982f209831218c398c25
hex 8c368c301e8c398c1f8c368c2c8c2f8c
hex 34238c388c3d1c8c3b8c38238c348c33
hex 238c3b8c36238c338c311e8c338c1f8c
hex 2f8c2c8c348c381c8c3b8c38178c3d8c
hex 3b148c388c31158c398c258c368c301e
hex 8c398c218c368c208c2f8c341c8c388c
hex 3d238c3b8c381c8c2f8c2e198c318c12
hex 982d0b8c33982c8c1c98381c8c348c36
hex 178c388c2f148c308c31158c398c2d8c
hex 368c301e8c398c1f8c368c2f208c348c
hex 382c8c3d8c1c8c3b8c38238c348c3317
hex 8c3b8c362d8c338c311e8c338c1f8c2f
hex 8c34208c348c381c8c3b8c238c3d8c3b
hex 148c388c31158c398c258c368c302a8c
hex 398c1f8c368c2f208c348c38238c3d8c
hex 288c3b8c38238c348c36198c388c3628
hex 8c348c331e8c348c288c318c2f239832
hex 1d8c331e8c3b17982f289831158c398c
hex 258c368c301e8c398c2b8c368c208c2f
hex 8c34238c388c3d1c8c3b8c382c8c348c
hex 33178c3b8c36238c338c311e8c338c2b
hex 8c2f8c208c348c381c8c3b8c38178c3d
hex 8c32148c388c31218c398c198c368c30
hex 1e8c398c218c368c208c2f8c34288c38
hex 8c3d178c3b8c381c8c2f8c2e198c318c
hex 12982d178c36982c8c1098179834108c
hex 2f8c318c3e8c331e982f238c318c2398
hex 23983312982f238c318c1e8c2f178c31
hex 168c33158c3414983b2c8c318c1c9823
hex 983414983b2c8c318c1c981d981e983d
hex 2d8c3b8c179823981b983d2d8c338c17
hex 9823981c983d2c8c348c179823981c98
hex 3d2c8c3b8c208c2f8c311f8c328c3f1e
hex 982f2d8c318c179823983f12982f2d8c
hex 318c128c2f178c3d168c33158c342098
hex 2f238c3d8c1c9823982c8c348c381c8c
hex 3b8c38178c3d8c32148c388c31158c39
hex 8c258c368c301e8c398c218c368c208c
hex 2f8c341c8c388c3d238c3b8c381c8c2f
hex 8c2e198c318c12982d178c36982c8c2c
hex 1098179834208c2f8c3d1f8c328c332a
hex 982f238c3d8c17982398331e982f238c
hex 3d8c128c2f178c31168c33218c381498
hex 2f238c318c1c982c983814982f238c31
hex 8c1c9829981e983d238c338c17982d98
hex 1b983d238c338c17982d981c983d238c
hex 348c17982c981c983d238c3b8c208c2f
hex 8c312b8c328c3f1e982f238c318c1798
hex 2d983f12982f238c318c128c3b238c31
hex 168c33158c3414982f238c3d8c289823
hex 98208c348c381c8c3b8c38238c3d8c3b
hex 148c388c31158c398c198c368c301e8c
hex 398c2d8c368c208c2f8c341c8c388c3d
hex 178c3b8c381c8c2f8c2e258c318c1298
hex 2d0b8c33982c8c2c109817983410ff
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; BITMAP DATA - Bob
PFBitmap0
hex 000000808080c0c0c0c0c0e0e0e0e0e0
hex e0e0e020000040c0c0c0808080000000
hex 00000000000000000000000000000000
hex 00000000000000000000000000000000
hex 00000000000000000000000000000000
hex 00000000000000000000800000008000
hex 80000000800000008000800080000000
hex 00000000800080008000800080008000
hex 80008000800080008000000000000000
hex 00000000000000000000000000000000
hex 00000000000000000000000000000000
PFBitmap1
hex 0000c0e0e0f0f0f8b8f8b8bcbcbcbcbe
hex be3e7ebf7f7f7f7fbfb7b7d3a3030101
hex 01010100020001020201060306050505
hex 0d020e0b0a0d0a0e0a0a1e0e0f1e0f0e
hex 1f0e0c0c0c0c08080828686028205040
hex b040d08068c0d0c0d1e0d0e0d0e5d0e6
hex dae6d3f5d7f9eafcfcfcfafffbfbfdf8
hex f9f8fcf0fcf8faf8f8f8fcf1fcf1fcf8
hex f4f8fcf8f4f8fcf9f4f8fdfdfdfefdff
hex ffffff7fff7f7f7f7f3f3f3f3f3e3f1f
hex 1f0f0f0f0f0707030301010000000000
PFBitmap2
hex 000000000000000000000000000000f0
hex f8f8fc3cbc16bc173b5f3b9b3b377b37
hex 776ff7effffffe7e7e3cfc78fcfc3c7c
hex fc3e1c1e0c0ecefcfefefffefffefdfd
hex fd79fa7a7a502c282830102060002040
hex 2040c02040514247466c4870c833e672
hex f6777f7f78793fba1c3c1f1f1f0f1782
hex 00200000890020008110400000200000
hex 400000200000800001a0cafafefbfeff
hex ffffffffffffffffbfffbfdf5bd55944
hex 4d696f2f7fbffffffffffffefe200000
PFBitmap3
hex 00000000000000000000000000c0f0f0
hex f0f0a050004000000000000000000010
hex 4000b070b0f0a04000100010f0408000
hex 50800000000050f0c080101030303070
hex 70f0e0e080000040004000a000004000
hex 000000000000000000000000004000c0
hex 80c0c080808000400000000000008000
hex 00000000800040000040000000004000
hex 00004000008000001070f0f0f0f0f0f0
hex f0f0f0f0d0f0b0c090c08080c0404040
hex 60406070a070f0f0f0f0f0f0f0000000
PFBitmap4
hex 000000000000000000000000000080c0
hex c06060e0303010380818080c040c0406
hex 04064606820342038303010341014101
hex 41614160703130f9f8fc787d060f0e1f
hex 0a1b1a199090a060a040000000000000
hex 00000000000008101820202010149a11
hex d9fffefea2f8a8c040f97f7f7f3e1c10
hex 00000000000000400800000080000000
hex 00880000000000000000008080c0f0f8
hex 7cfeffffffffffbfbf5d3f5d177d972d
hex b62ea3afb3aff7fffefefcf8e0000000
PFBitmap5
hex 00000000000000000000000000000000
hex 00000000000000000000000000000000
hex 00000000000000000000000000000100
hex 01000101030103020301030203020302
hex 03050301030202000200101808200800
hex 1028201030102830303832383a703a78
hex 3a78327a3a793a793b7b797a7d7a397c
hex 7b7c7d797d797d797c797a787c78687a
hex 6c787c7a687c6c7c3c7c7c3c7e3c7e3e
hex 3e3e3e3f3f1f1f1f1f0f0f0f0703030b
hex 03070101010100000000000000000000
; Epilogue
org $fffc
.word Start
.word Start