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sound.asm
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; indexes 0-19: freqhi=3
; indexes 20-47: freqhi=2
freqhitransition = 20
\ *******************************************************************
\ * Two interleaved tables mapping sound channel numbers to
\ * sound chip commands
\ *******************************************************************
.channelfreq
EQUB &80 ; channel 0 pitch (+bass implementation)
.channelvolume
EQUB &9F ; channel 0 volume
EQUB &A0 ; channel 1 pitch
EQUB &BF ; channel 1 volume
EQUB &C0 ; channel 2 pitch (which can be used with noise channel)
EQUB &DF ; channel 2 volume
EQUB &E0 ; noise pitch
EQUB &FF ; noise volume
\\--------------------------------------------------------------------------
\\ ****************************************************************************
\\ *
\\ * All the sound related code is here
\\ *
\\ ****************************************************************************
\\ Volume envelope definitions
\\ 1 2 3 4 5 6 7
.ve_attackrate EQUB 52, 24, 24, 48, 52, 52, 4
.ve_peak EQUB 52, 48, 24, 48, 52, 52, 44
.ve_sustaintime EQUB 4, 4, 0, 1, 0, 48, 4
.ve_releaserate EQUB 1, 4, 5, 4, 52, 1, 4
\\ Pitch envelope definitions
\\ 1 2 3 4 5 6 7 8 9
.pe_numsteps EQUB 6;, 3, 3, 3, 3, 3, 3, 3, 3
.pe_deflo EQUB LO(pe1);, LO(pe2), LO(pe3), LO(pe4), LO(pe5), LO(pe6), LO(pe7), LO(pe8), LO(pe9)
.pe_defhi EQUB HI(pe1);, HI(pe2), HI(pe3), HI(pe4), HI(pe5), HI(pe6), HI(pe7), HI(pe8), HI(pe9)
.pe1 EQUB 1, 0, 0, 255, 0, 0
;.pe2 EQUB 256-28, 16, 12 ; CEG triad
;.pe3 EQUB 256-36, 20, 16 ; CFA triad
;.pe4 EQUB 256-36, 12, 24 ; DFB triad
;.pe5 EQUB 256-36, 16, 20 ; EbGC triad
;.pe6 EQUB 256-28, 12, 16 ; CEbG triad
;.pe7 EQUB 256-36, 24, 12 ; EbAC triad
;.pe8 EQUB 256-24, 12, 12 ; GbAC triad
;.pe9 EQUB 256-32, 20, 12 ; GCEb triad
\\ Sound code entry point
.updatesound
LDX #6
.updatesoundloop
; see if a note has been requested on this channel
LDA notereq+1,X ; notereq MSB<>0 indicated a note request
BEQ nonewnote
; a note was requested - fill in details
; at (notereq,X) are:
; +0 pitch
; +1 pitch envelope number
; +2 volume envelope number
LDA (notereq,X)
STA pitch,X
JSR writepitch
INC notereq,X:BNE P%+4:INC notereq+1,X
LDA (notereq,X)
STA pitchenv,X
LDA #8:STA &FE40 ; easily used 16 cycles since the JSR writepitch
INC notereq,X:BNE P%+4:INC notereq+1,X
LDA (notereq,X)
STA volenv,X
TAY
LDA #0
STA notereq+1,X ; clear note request
STA pitchenvindex,X ; initialise pitch envelope pointer
STA volenvstage,X ; initialise volume envelope stage
; send vol/pitch to sound chip
LDA ve_attackrate-1,Y ; get initial volume from attack phase (-1 because valid indices start at 1)
STA volume,X
JSR writevolume
LDA #8 ; waste 16 cycles (6 from the RTS + 2
DEX:DEX ; + 2 + 2
STA &FE40 ; + 4)
BPL updatesoundloop
RTS
; No new note requested, so update what is already playing
.nonewnote
; Update volume if necessary
LDY volenv,X
BEQ novolumeenv
LDA volenvstage,X ; 0, 1-127 or &80
BMI release
BNE sustain
.attack
LDA volume,X
CMP ve_peak-1,Y
BCS sustain ; if already at peak, move to sustain phase
ADC ve_attackrate-1,Y
CMP ve_peak-1,Y
BCC updatevolume
LDA ve_peak-1,Y ; clamp at peak
STA volume,X
BNE updatevolume ; always taken
.sustain
LDA volenvstage,X
CMP ve_sustaintime-1,Y
INC volenvstage,X
BCC novolumeenv
.startrelease
LDA #128
STA volenvstage,X
.release
LDA volume,X
SEC
SBC ve_releaserate-1,Y
BPL P%+4
LDA #0
BNE updatevolume
STA volenv,X ; disable note, but still fall through so we write zero volume
STA pitchenv,X ; also stop pitch envelope update
.updatevolume
; Update volume here and send to sound chip
; Check against old value to see if anything has actually changed
TAY
EOR volume,X
AND #252
STY volume,X
BEQ volhasntchanged
TYA
JSR writevolume
LDA (0,X) ; waste 16 cycles (6 from the RTS + 6
LDA #8:STA &FE40 ; + 2 + most of the STA)
.volhasntchanged
.novolumeenv
; Update pitch if necessary
LDY pitchenv,X
BEQ nopitchenv
LDA pe_deflo-1,Y:STA pitchdata+1
LDA pe_defhi-1,Y:STA pitchdata+2
LDA pe_numsteps-1,Y:STA pitchsteps+1
LDY pitchenvindex,X
.pitchdata LDA &B9B9,Y ; self-modified
BEQ nochangepitch
CLC
ADC pitch,X
STA pitch,X
JSR writepitch
.nochangepitch
LDY pitchenvindex,X
INY
.pitchsteps CPY #0
BNE P%+4
LDY #0
STY pitchenvindex,X
LDA #8:STA &FE40
; iterate to next channel
.nopitchenv
DEX:DEX
BMI P%+5
JMP updatesoundloop
.exitsoundupdate
RTS
;-------------------------------------------------
.writevolume
; A = volume
; X = channel
; After calling this, wait at least 5 cycles, and then execute LDA #8:STA &FE40 or similar)
LSR A:LSR A
EOR channelvolume,X
STA &FE4F
LDY #0:STY &FE40
; Still pending: to pull sound chip enable high again
; Do it after the RTS to avoid idling unnecessarily
; (wait at least 5 cycles, and then execute LDA #8:STA &FE40 or similar)
RTS
.writepitchnoise
; A = note to be written to noise channel
; Still pending: to pull sound chip enable high again.
; Do it after the RTS to avoid idling unnecessarily
; (wait at least 5 cycles, and then execute LDA #8:STA &FE40 or similar)
ORA #&E0:STA &FE4F
LDY #0:STY &FE40
RTS
.writepitch
; A = note
; X = channel
; After calling this, wait at least 5 cycles, and then execute LDA #8:STA &FE40 or similar)
; Special handling for noise control
CPX #6
BEQ writepitchnoise
STX pitchchannel+1
; Find the octave and the note within the octave
LDX #0
CMP #48*4
BCC div48a
SBC #48*4
LDX #4
.div48a
CMP #48*2
BCC div48b
SBC #48*2
INX
INX
.div48b
CMP #48
BCC div48c
SBC #48
INX
.div48c
; X = octave number
; A = note within the octave
; Get 10-bit frequency for this note
; the top 2 bits are either 2 or 3, so we don't use a table for this
TAY
LDA #2
CPY #freqhitransition
ADC #0
EOR #1
STA soundtemp
LDA freqlo,Y
; Shift down according to octave
CPX #0
BEQ nooctaveshift
.octaveshift
LSR soundtemp
ROR A
DEX
BNE octaveshift
.nooctaveshift
; Write pitch to sound chip
; First, the low 4 bits
TAY ; preserve A
AND #15
.pitchchannel LDX #0 ; self-modified
ORA channelfreq,X
STA &FE4F
TYA ; get back A
; Pull sound chip enable low
LDY #0:STY &FE40
; Do some stuff while we have to wait 8us
ASL A:ROL soundtemp
ASL A:ROL soundtemp
ASL A:ROL soundtemp
ASL A:ROL soundtemp
; Pull sound chip enable high
LDA #8:STA &FE40
; Next, the top 6 bits
LDA soundtemp
STA &FE4F
; Pull sound chip enable low
STY &FE40 ; Y=0
; Still pending: to pull sound chip enable high again
; Do it after the RTS to avoid idling unnecessarily
; (wait at least 5 cycles, and then execute LDA #8:STA &FE40 or similar)
RTS
\\--------------------------------------------------------------------------
\\ At the beginning of the game, at some point, please configure the VIA as follows
\\ so that it's ready for the sound code.
\\ Configure sound chip ready for writing
\\ (Note, to access keyboard, write &03 to &FE40, but afterwards disable it
\\ again by writing &0B.)
LDA #&FF:STA &FE43
LDA #&0F:STA &FE42
LDA #&08:STA &FE40 ; sound chip enable pulled high (disabled for now)
LDA #&0B:STA &FE40 ; keyboard enable pulled high (disabled)
\\--------------------------------------------------------------------------
\\ To play a sound, put the address of a sound block in:
\\ notereq+0/notereq+1 - channel 0 (regular tone channel)
\\ notereq+2/notereq+3 - channel 1 (regular tone channel)
\\ notereq+4/notereq+5 - channel 2 (regular tone channel, also can be used as pitch for the noise channel)
\\ notereq+6/notereq+7 - channel 3 (the noise channel)
\\ Sound block contains:
\\ +0 - note pitch (in quarter semitones 0-255)
\\ +1 - pitch envelope index (0 = no pitch envelope)
\\ +2 - volume envelope index (must be >0, 0 is not valid)
;.testsoundblock:
;EQUB 240 ; pitch
;EQUB 0 ; slightly tremolo note
;EQUB 4 ; 'ding' volume envelope
; LDA #&FF:STA &FE43
; LDA #&0F:STA &FE42
; LDA #&08:STA &FE40 ; sound chip enable pulled high (disabled for now)
; LDA #&0B:STA &FE40 ; keyboard enable pulled high (disabled)
; LDA #LO(testsoundblock):STA notereq+0
; LDA #HI(testsoundblock):STA notereq+1 ; always store MSB last