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cd433ee4c5e4538faabd1a91b5e408ed666249c1
c64-demo/music.asm
T
mr.zero cd433ee4c5 third music channel
2026-07-14 19:11:51 +02:00

273 lines
9.5 KiB
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; -----------------------------------------------------------
; music.asm - SID music driver
; called once per frame from wait_frame
; music_init: clear SID, set instruments, restart the song
; music_play: pattern player tick (once per frame)
; music_mute / music_unmute: volume control
;
; The tune is track 0 ("room work") of the Impostor TIC-80
; cart, converted from inc/meta/meta.assets.lua:
; voice 1: bass line (sfx 59 -> SID 50% pulse; the original
; is a soft sine, but pulse carries better here)
; voice 2: drums (sfx 61, TIC-80 noise -> SID noise,
; C-1 = kick, C-4 = snare)
; voice 3: echo canon: repeats the bass melody 2 rows
; (~170 ms) later, 3 octaves up, with the sfx 56
; pluck timbre (triangle, decaying envelope);
; repeated notes bounce up one more octave. The
; echo data lives on the same 128-row grid as the
; bass, so the two voices can never drift apart.
; Original timing: tempo 150, speed 5 = 12 rows/s at 60 Hz.
; On PAL (50 Hz) that is 25 frames per 6 rows, so every
; sixth row lasts 5 frames instead of 4 (see spd_tbl).
; -----------------------------------------------------------
; ---- SID registers ----
SID_BASE = $d400
SID_V1_FL = SID_BASE+0 ; voice 1 frequency low
SID_V1_FH = SID_BASE+1 ; voice 1 frequency high
SID_V1_PL = SID_BASE+2 ; voice 1 pulse width low
SID_V1_PH = SID_BASE+3 ; voice 1 pulse width high
SID_V1_CR = SID_BASE+4 ; voice 1 control (gate, waveform)
SID_V1_AD = SID_BASE+5 ; voice 1 attack/decay
SID_V1_SR = SID_BASE+6 ; voice 1 sustain/release
SID_V2_FL = SID_BASE+7 ; voice 2 frequency low
SID_V2_FH = SID_BASE+8 ; voice 2 frequency high
SID_V2_PL = SID_BASE+9 ; voice 2 pulse width low
SID_V2_PH = SID_BASE+10 ; voice 2 pulse width high
SID_V2_CR = SID_BASE+11 ; voice 2 control
SID_V2_AD = SID_BASE+12 ; voice 2 attack/decay
SID_V2_SR = SID_BASE+13 ; voice 2 sustain/release
SID_V3_FL = SID_BASE+14 ; voice 3 frequency low
SID_V3_FH = SID_BASE+15 ; voice 3 frequency high
SID_V3_PL = SID_BASE+16 ; voice 3 pulse width low
SID_V3_PH = SID_BASE+17 ; voice 3 pulse width high
SID_V3_CR = SID_BASE+18 ; voice 3 control
SID_V3_AD = SID_BASE+19 ; voice 3 attack/decay
SID_V3_SR = SID_BASE+20 ; voice 3 sustain/release
SID_FC_LO = SID_BASE+21 ; filter cutoff low (bits 0-2)
SID_FC_HI = SID_BASE+22 ; filter cutoff high
SID_FCTL = SID_BASE+23 ; filter resonance + voice routing
SID_VOL = SID_BASE+24 ; filter mode (hi nibble) + master volume (lo nibble)
; ---- waveform control values ----
BASS_ON = $41 ; pulse + gate (much louder than triangle,
BASS_OFF = $40 ; so the bass stands out from the drums)
DRUM_ON = $81 ; noise + gate
DRUM_OFF = $80
LEAD_ON = $11 ; triangle + gate (soft pluck, stays
LEAD_OFF = $10 ; behind the bass and the drums)
SONG_LEN = 128 ; 2 frames x 64 rows
; ---- initialize SID and restart the song ----
music_init:
ldx #24
lda #0
mi_clr:
sta SID_BASE,x
dex
bpl mi_clr
lda #$00 ; bass: instant attack, full sustain
sta SID_V1_AD
lda #$f3 ; short release, so the tail does not
sta SID_V1_SR ; fill the rests between the notes
lda #$08 ; bass pulse width: 50% square, the
sta SID_V1_PH ; fattest setting ($0800 of $0fff)
lda #$00
sta SID_V1_PL
lda #$04 ; drums: instant attack, ~110 ms decay
sta SID_V2_AD
lda #$00
sta SID_V2_SR
lda #$06 ; lead: pluck, ~200 ms decay to zero
sta SID_V3_AD ; (matches the sfx 56 envelope)
lda #$00
sta SID_V3_SR
lda #$0f ; master volume = 15
sta SID_VOL
lda #0
sta mus_muted
sta mus_row
sta mus_spd_ix
sta mus_bcut
lda #1 ; first music_play tick starts row 0
sta mus_tick
rts
; ---- play one tick: called once per frame ----
music_play:
lda mus_muted
bne mp_done ; muted: song position frozen too
lda mus_bcut ; scheduled bass gate-off: opens a small
beq mp_tick ; gap before the next note, so the
dec mus_bcut ; notes don't run into each other
bne mp_tick
lda #BASS_OFF
sta SID_V1_CR
mp_tick:
dec mus_tick
beq mp_row
mp_done:
rts
mp_row:
ldx mus_spd_ix ; reload row length (4,4,4,4,4,5 frames)
lda spd_tbl,x
sta mus_tick
inx
cpx #6
bne mp_spd_ok
ldx #0
mp_spd_ok:
stx mus_spd_ix
ldx mus_row
; ---- voice 1: bass ----
lda bass_pat,x
beq mp_drums ; 0 = no event
cmp #1
bne mp_bass_note
lda #BASS_OFF ; 1 = key off
sta SID_V1_CR
jmp mp_drums
mp_bass_note:
and #$7f ; $80|n = trigger note n
tay
lda bass_flo,y
sta SID_V1_FL
lda bass_fhi,y
sta SID_V1_FH
lda #BASS_OFF ; gate off + on restarts the envelope
sta SID_V1_CR
lda #BASS_ON
sta SID_V1_CR
; ---- voice 2: drums ----
mp_drums:
lda drum_pat,x
beq mp_lead
cmp #1
bne mp_drum_note
lda #DRUM_OFF
sta SID_V2_CR
jmp mp_lead
mp_drum_note:
and #$7f
tay
lda drum_flo,y
sta SID_V2_FL
lda drum_fhi,y
sta SID_V2_FH
lda #DRUM_OFF
sta SID_V2_CR
lda #DRUM_ON
sta SID_V2_CR
; ---- voice 3: arpeggio lead ----
mp_lead:
lda lead_pat,x ; only notes here, no key-off events:
beq mp_next ; the envelope decays to silence
and #$7f
tay
lda lead_flo,y
sta SID_V3_FL
lda lead_fhi,y
sta SID_V3_FH
lda #LEAD_OFF
sta SID_V3_CR
lda #LEAD_ON
sta SID_V3_CR
mp_next:
inx
cpx #SONG_LEN
bne mp_store
ldx #0 ; loop the song
stx mus_spd_ix ; restart the 4,4,4,4,4,5 cycle with it
mp_store:
stx mus_row
lda bass_pat,x ; peek at the next row: if a note comes,
bpl mp_nocut ; cut the bass 2 frames before it
lda mus_tick
sec
sbc #2
sta mus_bcut
mp_nocut:
rts
; ---- mute: silence SID ----
music_mute:
lda #$00
sta SID_VOL
rts
; ---- unmute: restore volume ----
music_unmute:
lda #$0f
sta SID_VOL
rts
; ---- state ----
mus_muted: !byte 0 ; 1 = muted
mus_row: !byte 0 ; song position (0..SONG_LEN-1)
mus_tick: !byte 1 ; frames left of the current row
mus_spd_ix: !byte 0 ; index into spd_tbl
mus_bcut: !byte 0 ; frames until the pre-note bass gate-off
; (0 = none scheduled)
spd_tbl: !byte 4,4,4,4,4,5 ; 25 frames / 6 rows = 12 rows/s
; ---- note tables (PAL SID: reg = Hz * 16777216 / 985248) ----
; bass: 0 = C-2, 1 = A#1, 2 = D#2, 3 = F-2
bass_flo: !byte $5a,$e0,$2d,$cf
bass_fhi: !byte $04,$03,$05,$05
; drums: noise pitch from the TIC-80 note (x32 waveform steps)
; 0 = C-1 kick (low rumble), 1 = C-4 snare (bright)
drum_flo: !byte $9c,$ff
drum_fhi: !byte $45,$ff
; lead echo: bass notes +3 octaves (0-3), +4 octaves (4-7)
; 0 = C-5, 1 = A#4, 2 = D#5, 3 = F-5, 4 = C-6, 5 = A#5, 6 = D#6, 7 = F-6
lead_flo: !byte $ce,$02,$64,$76,$9c,$04,$c8,$eb
lead_fhi: !byte $22,$1f,$29,$2e,$45,$3e,$52,$5c
; ---- pattern data: one byte per row per voice ----
; $00 = nothing, $01 = key off, $80|n = play note n
bass_pat:
!byte $80,$00,$00,$00,$01,$00,$80,$00,$01,$00,$00,$00,$81,$00,$80,$00
!byte $01,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
!byte $80,$00,$00,$00,$01,$00,$80,$00,$01,$00,$00,$00,$81,$00,$80,$00
!byte $01,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
!byte $80,$00,$00,$00,$01,$00,$80,$00,$01,$00,$00,$00,$81,$00,$80,$00
!byte $01,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
!byte $82,$00,$82,$00,$01,$00,$82,$00,$01,$00,$00,$00,$82,$00,$83,$00
!byte $01,$00,$83,$00,$01,$00,$83,$00,$83,$00,$01,$00,$83,$00,$01,$00
drum_pat:
!byte $80,$00,$00,$00,$00,$00,$00,$00,$81,$00,$00,$00,$00,$00,$00,$00
!byte $80,$00,$00,$00,$00,$00,$80,$00,$81,$00,$00,$00,$00,$00,$00,$00
!byte $80,$00,$00,$00,$00,$00,$00,$00,$81,$00,$00,$00,$00,$00,$00,$00
!byte $80,$00,$00,$00,$00,$00,$80,$00,$81,$00,$00,$00,$00,$00,$00,$00
!byte $80,$00,$00,$00,$00,$00,$00,$00,$81,$00,$00,$00,$00,$00,$00,$00
!byte $80,$00,$00,$00,$00,$00,$80,$00,$81,$00,$00,$00,$00,$00,$00,$00
!byte $80,$00,$00,$00,$00,$00,$00,$00,$81,$00,$00,$00,$00,$00,$00,$00
!byte $80,$00,$00,$00,$00,$00,$80,$00,$81,$00,$00,$00,$00,$00,$00,$00
; the bass_pat notes shifted 2 rows later; repeated notes take the
; octave-up variant (indices 4-7), alternating with the base octave
lead_pat:
!byte $00,$00,$80,$00,$00,$00,$00,$00,$84,$00,$00,$00,$00,$00,$81,$00
!byte $80,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
!byte $00,$00,$84,$00,$00,$00,$00,$00,$80,$00,$00,$00,$00,$00,$81,$00
!byte $80,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
!byte $00,$00,$84,$00,$00,$00,$00,$00,$80,$00,$00,$00,$00,$00,$81,$00
!byte $80,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
!byte $00,$00,$82,$00,$86,$00,$00,$00,$82,$00,$00,$00,$00,$00,$86,$00
!byte $83,$00,$00,$00,$87,$00,$00,$00,$83,$00,$87,$00,$00,$00,$83,$00
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