engine_1.asm

; The first of three duplicated sound engines.

Audio1_UpdateMusic::
	ld c, CHAN1
.loop
	ld b, 0
	ld hl, wChannelSoundIDs
	add hl, bc
	ld a, [hl]
	and a
	jr z, .nextChannel
	ld a, c
	cp CHAN5
	jr nc, .applyAffects ; if sfx channel
	ld a, [wMuteAudioAndPauseMusic]
	and a
	jr z, .applyAffects
	bit BIT_MUTE_AUDIO, a
	jr nz, .nextChannel
	set BIT_MUTE_AUDIO, a
	ld [wMuteAudioAndPauseMusic], a
	xor a ; disable all channels' output
	ldh [rAUDTERM], a
	ldh [rAUD3ENA], a
	ld a, AUD3ENA_ON
	ldh [rAUD3ENA], a
	jr .nextChannel
.applyAffects
	call Audio1_ApplyMusicAffects
.nextChannel
	ld a, c
	inc c ; inc channel number
	cp CHAN8
	jr nz, .loop
	ret

; this routine checks flags for music effects currently applied
; to the channel and calls certain functions based on flags.
Audio1_ApplyMusicAffects:
	ld b, $0
	ld hl, wChannelNoteDelayCounters ; delay until next note
	add hl, bc
	ld a, [hl]
	cp 1 ; if the delay is 1, play next note
	jp z, Audio1_PlayNextNote
	dec a ; otherwise, decrease the delay timer
	ld [hl], a
	ld a, c
	cp CHAN5
	jr nc, .startChecks ; if a sfx channel
	ld hl, wChannelSoundIDs + CHAN5
	add hl, bc
	ld a, [hl]
	and a
	jr z, .startChecks
	ret
.startChecks
	ld hl, wChannelFlags1
	add hl, bc
	bit BIT_ROTATE_DUTY_CYCLE, [hl]
	jr z, .checkForExecuteMusic
	call Audio1_ApplyDutyCyclePattern
.checkForExecuteMusic
	ld b, 0
	ld hl, wChannelFlags2
	add hl, bc
	bit BIT_EXECUTE_MUSIC, [hl]
	jr nz, .checkForPitchSlide
	ld hl, wChannelFlags1
	add hl, bc
	bit BIT_NOISE_OR_SFX, [hl]
	jr nz, .skipPitchSlideVibrato
.checkForPitchSlide
	ld hl, wChannelFlags1
	add hl, bc
	bit BIT_PITCH_SLIDE_ON, [hl]
	jr z, .checkVibratoDelay
	jp Audio1_ApplyPitchSlide
.checkVibratoDelay
	ld hl, wChannelVibratoDelayCounters
	add hl, bc
	ld a, [hl]
	and a ; check if delay is over
	jr z, .checkForVibrato
	dec [hl] ; otherwise, dec delay
.skipPitchSlideVibrato
	ret
.checkForVibrato
	ld hl, wChannelVibratoExtents
	add hl, bc
	ld a, [hl]
	and a
	jr nz, .vibrato
	ret ; no vibrato
.vibrato
	ld d, a
	ld hl, wChannelVibratoRates
	add hl, bc
	ld a, [hl]
	and $f
	and a
	jr z, .applyVibrato
	dec [hl] ; decrement counter
	ret
.applyVibrato
	ld a, [hl]
	swap [hl]
	or [hl]
	ld [hl], a ; reload the counter
	ld hl, wChannelFrequencyLowBytes
	add hl, bc
	ld e, [hl] ; get note pitch
	ld hl, wChannelFlags1
	add hl, bc
; This is the only code that sets/resets the vibrato direction bit, so it
; continuously alternates which path it takes.
	bit BIT_VIBRATO_DIRECTION, [hl]
	jr z, .unset
	res BIT_VIBRATO_DIRECTION, [hl]
	ld a, d
	and $f
	ld d, a
	ld a, e
	sub d
	jr nc, .noCarry
	ld a, 0
.noCarry
	jr .done
.unset
	set BIT_VIBRATO_DIRECTION, [hl]
	ld a, d
	and $f0
	swap a
	add e
	jr nc, .done
	ld a, $ff
.done
	ld d, a
	ld b, REG_FREQUENCY_LO
	call Audio1_GetRegisterPointer
	ld [hl], d
	ret

; this routine executes all music commands that take up no time,
; like tempo changes, duty cycle changes etc. and doesn't return
; until the first note is reached
Audio1_PlayNextNote:
; reload the vibrato delay counter
	ld hl, wChannelVibratoDelayCounterReloadValues
	add hl, bc
	ld a, [hl]
	ld hl, wChannelVibratoDelayCounters
	add hl, bc
	ld [hl], a

	ld hl, wChannelFlags1
	add hl, bc
	res BIT_PITCH_SLIDE_ON, [hl]
	res BIT_PITCH_SLIDE_DECREASING, [hl]
	call Audio1_sound_ret
	ret

Audio1_sound_ret:
	call Audio1_GetNextMusicByte
	ld d, a
	cp sound_ret_cmd
	jp nz, Audio1_sound_call
	ld b, 0
	ld hl, wChannelFlags1
	add hl, bc
	bit BIT_SOUND_CALL, [hl]
	jr nz, .returnFromCall
	ld a, c
	cp CHAN4
	jr nc, .noiseOrSfxChannel
	jr .disableChannelOutput
.noiseOrSfxChannel
	res BIT_NOISE_OR_SFX, [hl]
	ld hl, wChannelFlags2
	add hl, bc
	res BIT_EXECUTE_MUSIC, [hl]
	cp CHAN7
	jr nz, .skipSfxChannel3
; restart hardware channel 3 (wave channel) output
	ld a, AUD3ENA_OFF
	ldh [rAUD3ENA], a
	ld a, AUD3ENA_ON
	ldh [rAUD3ENA], a
.skipSfxChannel3
	jr nz, .dontDisable
	ld a, [wDisableChannelOutputWhenSfxEnds]
	and a
	jr z, .dontDisable
	xor a
	ld [wDisableChannelOutputWhenSfxEnds], a
	jr .disableChannelOutput
.dontDisable
	jr .afterDisable
.returnFromCall
	res BIT_SOUND_CALL, [hl]
	ld d, $0
	ld a, c
	add a
	ld e, a
	ld hl, wChannelCommandPointers
	add hl, de
	push hl ; store current channel address
	ld hl, wChannelReturnAddresses
	add hl, de
	ld e, l
	ld d, h
	pop hl
	ld a, [de]
	ld [hli], a
	inc de
	ld a, [de]
	ld [hl], a ; loads channel address to return to
	jp Audio1_sound_ret
.disableChannelOutput
	ld hl, Audio1_HWChannelDisableMasks
	add hl, bc
	ldh a, [rAUDTERM]
	and [hl]
	ldh [rAUDTERM], a
.afterDisable
	ld a, [wChannelSoundIDs + CHAN5]
	cp CRY_SFX_START
	jr nc, .maybeCry
	jr .skipCry
.maybeCry
	ld a, [wChannelSoundIDs + CHAN5]
	cp CRY_SFX_END
	jr z, .skipCry
	jr c, .cry
	jr .skipCry
.cry
	ld a, c
	cp CHAN5
	jr z, .skipRewind
	call Audio1_GoBackOneCommandIfCry
	ret c
.skipRewind
	ld a, [wSavedVolume]
	ldh [rAUDVOL], a
	xor a
	ld [wSavedVolume], a
.skipCry
	ld hl, wChannelSoundIDs
	add hl, bc
	ld [hl], b
	ret

Audio1_sound_call:
	cp sound_call_cmd
	jp nz, Audio1_sound_loop
	call Audio1_GetNextMusicByte
	push af
	call Audio1_GetNextMusicByte
	ld d, a
	pop af
	ld e, a
	push de ; store pointer
	ld d, $0
	ld a, c
	add a
	ld e, a
	ld hl, wChannelCommandPointers
	add hl, de
	push hl
	ld hl, wChannelReturnAddresses
	add hl, de
	ld e, l
	ld d, h
	pop hl
	ld a, [hli]
	ld [de], a
	inc de
	ld a, [hld]
	ld [de], a ; copy current channel address
	pop de
	ld [hl], e
	inc hl
	ld [hl], d ; overwrite current address with pointer
	ld b, $0
	ld hl, wChannelFlags1
	add hl, bc
	set BIT_SOUND_CALL, [hl] ; set the call flag
	jp Audio1_sound_ret

Audio1_sound_loop:
	cp sound_loop_cmd
	jp nz, Audio1_note_type
	call Audio1_GetNextMusicByte
	ld e, a
	and a
	jr z, .infiniteLoop
	ld b, 0
	ld hl, wChannelLoopCounters
	add hl, bc
	ld a, [hl]
	cp e
	jr nz, .loopAgain
	ld a, $1 ; if no more loops to make,
	ld [hl], a
	call Audio1_GetNextMusicByte ; skip pointer
	call Audio1_GetNextMusicByte
	jp Audio1_sound_ret
.loopAgain ; inc loop count
	inc a
	ld [hl], a
	; fall through
.infiniteLoop ; overwrite current address with pointer
	call Audio1_GetNextMusicByte
	push af
	call Audio1_GetNextMusicByte
	ld b, a
	ld d, $0
	ld a, c
	add a
	ld e, a
	ld hl, wChannelCommandPointers
	add hl, de
	pop af
	ld [hli], a
	ld [hl], b
	jp Audio1_sound_ret

Audio1_note_type:
	and $f0
	cp note_type_cmd
	jp nz, Audio1_toggle_perfect_pitch
	ld a, d
	and $f
	ld b, $0
	ld hl, wChannelNoteSpeeds
	add hl, bc
	ld [hl], a ; store low nibble as speed
	ld a, c
	cp CHAN4
	jr z, .noiseChannel ; noise channel has 0 params
	call Audio1_GetNextMusicByte
	ld d, a
	ld a, c
	cp CHAN3
	jr z, .musicChannel3
	cp CHAN7
	jr nz, .skipChannel3
	ld hl, wSfxWaveInstrument
	jr .channel3
.musicChannel3
	ld hl, wMusicWaveInstrument
.channel3
	ld a, d
	and $f
	ld [hl], a ; store low nibble of param as wave instrument
	ld a, d
	and $30
	sla a
	ld d, a
	; fall through

	; if channel 3, store high nibble as volume
	; else, store volume (high nibble) and fade (low nibble)
.skipChannel3
	ld b, 0
	ld hl, wChannelVolumes
	add hl, bc
	ld [hl], d
.noiseChannel
	jp Audio1_sound_ret

Audio1_toggle_perfect_pitch:
	ld a, d
	cp toggle_perfect_pitch_cmd
	jr nz, Audio1_vibrato
	ld b, 0
	ld hl, wChannelFlags1
	add hl, bc
	ld a, [hl]
	xor 1 << BIT_PERFECT_PITCH
	ld [hl], a
	jp Audio1_sound_ret

Audio1_vibrato:
	cp vibrato_cmd
	jr nz, Audio1_pitch_slide
	call Audio1_GetNextMusicByte
	ld b, 0
	ld hl, wChannelVibratoDelayCounters
	add hl, bc
	ld [hl], a ; store delay
	ld hl, wChannelVibratoDelayCounterReloadValues
	add hl, bc
	ld [hl], a ; store delay
	call Audio1_GetNextMusicByte
	ld d, a

; The high nybble of the command byte is the extent of the vibrato.
; Let n be the extent.
; The upper nybble of the channel's byte in the wChannelVibratoExtents
; array will store the extent above the note: (n / 2) + (n % 2).
; The lower nybble will store the extent below the note: (n / 2).
; These two values add to the total extent, n.
	and $f0
	swap a
	ld b, 0
	ld hl, wChannelVibratoExtents
	add hl, bc
	srl a
	ld e, a
	adc b
	swap a
	or e
	ld [hl], a

; The low nybble of the command byte is the rate of the vibrato.
; The high and low nybbles of the channel's byte in the wChannelVibratoRates
; array are both initialised to this value because the high nybble is the
; counter reload value and the low nybble is the counter itself, which should
; start at its value upon reload.
	ld a, d
	and $f
	ld d, a
	ld hl, wChannelVibratoRates
	add hl, bc
	swap a
	or d
	ld [hl], a

	jp Audio1_sound_ret

Audio1_pitch_slide:
	cp pitch_slide_cmd
	jr nz, Audio1_duty_cycle
	call Audio1_GetNextMusicByte
	ld b, 0
	ld hl, wChannelPitchSlideLengthModifiers
	add hl, bc
	ld [hl], a
	call Audio1_GetNextMusicByte
	ld d, a
	and $f0
	swap a
	ld b, a
	ld a, d
	and $f
	call Audio1_CalculateFrequency
	ld b, 0
	ld hl, wChannelPitchSlideTargetFrequencyHighBytes
	add hl, bc
	ld [hl], d
	ld hl, wChannelPitchSlideTargetFrequencyLowBytes
	add hl, bc
	ld [hl], e
	ld b, 0
	ld hl, wChannelFlags1
	add hl, bc
	set BIT_PITCH_SLIDE_ON, [hl]
	call Audio1_GetNextMusicByte
	ld d, a
	jp Audio1_note_length

Audio1_duty_cycle:
	cp duty_cycle_cmd
	jr nz, Audio1_tempo
	call Audio1_GetNextMusicByte
	rrca
	rrca
	and $c0
	ld b, 0
	ld hl, wChannelDutyCycles
	add hl, bc
	ld [hl], a ; store duty cycle
	jp Audio1_sound_ret

Audio1_tempo:
	cp tempo_cmd
	jr nz, Audio1_stereo_panning
	ld a, c
	cp CHAN5
	jr nc, .sfxChannel
	call Audio1_GetNextMusicByte
	ld [wMusicTempo], a ; store first param
	call Audio1_GetNextMusicByte
	ld [wMusicTempo + 1], a ; store second param
	xor a
	ld [wChannelNoteDelayCountersFractionalPart], a ; clear RAM
	ld [wChannelNoteDelayCountersFractionalPart + 1], a
	ld [wChannelNoteDelayCountersFractionalPart + 2], a
	ld [wChannelNoteDelayCountersFractionalPart + 3], a
	jr .musicChannelDone
.sfxChannel
	call Audio1_GetNextMusicByte
	ld [wSfxTempo], a ; store first param
	call Audio1_GetNextMusicByte
	ld [wSfxTempo + 1], a ; store second param
	xor a
	ld [wChannelNoteDelayCountersFractionalPart + 4], a ; clear RAM
	ld [wChannelNoteDelayCountersFractionalPart + 5], a
	ld [wChannelNoteDelayCountersFractionalPart + 6], a
	ld [wChannelNoteDelayCountersFractionalPart + 7], a
.musicChannelDone
	jp Audio1_sound_ret

Audio1_stereo_panning:
	cp stereo_panning_cmd
	jr nz, Audio1_unknownmusic0xef
	call Audio1_GetNextMusicByte
	ld [wStereoPanning], a ; store panning
	jp Audio1_sound_ret

; this appears to never be used
Audio1_unknownmusic0xef:
	cp unknownmusic0xef_cmd
	jr nz, Audio1_duty_cycle_pattern
	call Audio1_GetNextMusicByte
	push bc
	call Audio1_PlaySound
	pop bc
	ld a, [wDisableChannelOutputWhenSfxEnds]
	and a
	jr nz, .skip
	ld a, [wChannelSoundIDs + CHAN8]
	ld [wDisableChannelOutputWhenSfxEnds], a
	xor a
	ld [wChannelSoundIDs + CHAN8], a
.skip
	jp Audio1_sound_ret

Audio1_duty_cycle_pattern:
	cp duty_cycle_pattern_cmd
	jr nz, Audio1_volume
	call Audio1_GetNextMusicByte
	ld b, 0
	ld hl, wChannelDutyCyclePatterns
	add hl, bc
	ld [hl], a ; store full pattern
	and %11000000
	ld hl, wChannelDutyCycles
	add hl, bc
	ld [hl], a ; store first duty cycle
	ld hl, wChannelFlags1
	add hl, bc
	set BIT_ROTATE_DUTY_CYCLE, [hl]
	jp Audio1_sound_ret

Audio1_volume:
	cp volume_cmd
	jr nz, Audio1_execute_music
	call Audio1_GetNextMusicByte
	ldh [rAUDVOL], a ; store volume
	jp Audio1_sound_ret

Audio1_execute_music:
	cp execute_music_cmd
	jr nz, Audio1_octave
	ld b, $0
	ld hl, wChannelFlags2
	add hl, bc
	set BIT_EXECUTE_MUSIC, [hl]
	jp Audio1_sound_ret

Audio1_octave:
	and $f0
	cp octave_cmd
	jr nz, Audio1_sfx_note
	ld hl, wChannelOctaves
	ld b, 0
	add hl, bc
	ld a, d
	and $f
	ld [hl], a ; store low nibble as octave
	jp Audio1_sound_ret

; sfx_note is either square_note or noise_note depending on the channel
Audio1_sfx_note:
	cp sfx_note_cmd
	jr nz, Audio1_pitch_sweep
	ld a, c
	cp CHAN4 ; is this a noise or sfx channel?
	jr c, Audio1_pitch_sweep ; no
	ld b, 0
	ld hl, wChannelFlags2
	add hl, bc
	bit BIT_EXECUTE_MUSIC, [hl] ; is execute_music being used?
	jr nz, Audio1_pitch_sweep ; yes
	call Audio1_note_length

; This code seems to do the same thing as what Audio1_ApplyDutyCycleAndSoundLength
; does below.
	ld d, a
	ld b, 0
	ld hl, wChannelDutyCycles
	add hl, bc
	ld a, [hl]
	or d
	ld d, a
	ld b, REG_DUTY_SOUND_LEN
	call Audio1_GetRegisterPointer
	ld [hl], d

	call Audio1_GetNextMusicByte
	ld d, a
	ld b, REG_VOLUME_ENVELOPE
	call Audio1_GetRegisterPointer
	ld [hl], d
	call Audio1_GetNextMusicByte
	ld e, a
	ld a, c
	cp CHAN8
	ld a, 0
	jr z, .skip
; Channels 1 through 3 have 2 registers that control frequency, but the noise
; channel a single register (the polynomial counter) that controls frequency,
; so this command has one less byte on the noise channel.
	push de
	call Audio1_GetNextMusicByte
	pop de
.skip
	ld d, a
	push de
	call Audio1_ApplyDutyCycleAndSoundLength
	call Audio1_EnableChannelOutput
	pop de
	call Audio1_ApplyWavePatternAndFrequency
	ret

Audio1_pitch_sweep:
	ld a, c
	cp CHAN5
	jr c, Audio1_note ; if not a sfx
	ld a, d
	cp pitch_sweep_cmd
	jr nz, Audio1_note
	ld b, $0
	ld hl, wChannelFlags2
	add hl, bc
	bit BIT_EXECUTE_MUSIC, [hl]
	jr nz, Audio1_note ; no
	call Audio1_GetNextMusicByte
	ldh [rAUD1SWEEP], a
	jp Audio1_sound_ret

Audio1_note:
	ld a, c
	cp CHAN4
	jr nz, Audio1_note_length ; if not noise channel
	ld a, d
	and $f0
	cp drum_note_cmd
	jr z, .drum_note
	jr nc, Audio1_note_length

	; this executes when on the noise channel and
	; the command id is less than drum_note_cmd ($b0)
	; in this case, the upper nybble is used as the noise instrument ($1-$a)
	; and the lower nybble is the length minus 1 (0-15)
	; however, this doesn't work for instrument #2 because the command id
	; is captured by the noise_note command (command id $2x)
	; this essentially acts like a drum_note command that is only 1 byte
	; instead of 2 and can only be used with instruments 1 and 3 through 10
	; this is unused by the game
	swap a
	ld b, a
	ld a, d
	and $f
	ld d, a
	ld a, b
	push de
	push bc
	jr .playDnote

.drum_note
	ld a, d
	and $f
	push af
	push bc
	call Audio1_GetNextMusicByte ; get drum_note instrument
.playDnote
	ld d, a
	ld a, [wDisableChannelOutputWhenSfxEnds]
	and a
	jr nz, .skipDnote
	ld a, d
	call Audio1_PlaySound
.skipDnote
	pop bc
	pop de

Audio1_note_length:
	ld a, d
	push af
	and $f
	inc a
	ld b, 0
	ld e, a  ; store note length (in 16ths)
	ld d, b
	ld hl, wChannelNoteSpeeds
	add hl, bc
	ld a, [hl]
	ld l, b
	call Audio1_MultiplyAdd
	ld a, c
	cp CHAN5
	jr nc, .sfxChannel
	ld a, [wMusicTempo]
	ld d, a
	ld a, [wMusicTempo + 1]
	ld e, a
	jr .skip
.sfxChannel
	ld d, $1
	ld e, $0
	cp CHAN8
	jr z, .skip ; if noise channel
	call Audio1_SetSfxTempo
	ld a, [wSfxTempo]
	ld d, a
	ld a, [wSfxTempo + 1]
	ld e, a
.skip
	ld a, l ; a = note_length * note_speed
	ld b, 0
	ld hl, wChannelNoteDelayCountersFractionalPart
	add hl, bc
	ld l, [hl]
	call Audio1_MultiplyAdd
	ld e, l
	ld d, h ; de = note_delay_frac_part + (note_length * note_speed * tempo)
	ld hl, wChannelNoteDelayCountersFractionalPart
	add hl, bc
	ld [hl], e
	ld a, d
	ld hl, wChannelNoteDelayCounters
	add hl, bc
	ld [hl], a
	ld hl, wChannelFlags2
	add hl, bc
	bit BIT_EXECUTE_MUSIC, [hl]
	jr nz, Audio1_note_pitch
	ld hl, wChannelFlags1
	add hl, bc
	bit BIT_NOISE_OR_SFX, [hl]
	jr z, Audio1_note_pitch
	pop hl
	ret

Audio1_note_pitch:
	pop af
	and $f0
	cp rest_cmd
	jr nz, .notRest
	ld a, c
	cp CHAN5
	jr nc, .next
; If this isn't an SFX channel, try the corresponding SFX channel.
	ld hl, wChannelSoundIDs + CHAN5
	add hl, bc
	ld a, [hl]
	and a
	jr nz, .done
	; fall through
.next
	ld a, c
	cp CHAN3
	jr z, .channel3
	cp CHAN7
	jr nz, .notChannel3
.channel3
	ld b, 0
	ld hl, Audio1_HWChannelDisableMasks
	add hl, bc
	ldh a, [rAUDTERM]
	and [hl]
	ldh [rAUDTERM], a ; disable hardware channel 3's output
	jr .done
.notChannel3
	ld b, REG_VOLUME_ENVELOPE
	call Audio1_GetRegisterPointer
	ld a, $8 ; fade in sound
	ld [hli], a
	inc hl
	ld a, $80 ; restart sound
	ld [hl], a
.done
	ret
.notRest
	swap a
	ld b, 0
	ld hl, wChannelOctaves
	add hl, bc
	ld b, [hl]
	call Audio1_CalculateFrequency
	ld b, 0
	ld hl, wChannelFlags1
	add hl, bc
	bit BIT_PITCH_SLIDE_ON, [hl]
	jr z, .skipPitchSlide
	call Audio1_InitPitchSlideVars
.skipPitchSlide
	push de
	ld a, c
	cp CHAN5
	jr nc, .sfxChannel ; if sfx channel
; If this isn't an SFX channel, try the corresponding SFX channel.
	ld hl, wChannelSoundIDs + CHAN5
	ld d, 0
	ld e, a
	add hl, de
	ld a, [hl]
	and a
	jr nz, .noSfx
	jr .sfxChannel
.noSfx
	pop de
	ret
.sfxChannel
	ld b, 0
	ld hl, wChannelVolumes
	add hl, bc
	ld d, [hl]
	ld b, REG_VOLUME_ENVELOPE
	call Audio1_GetRegisterPointer
	ld [hl], d
	call Audio1_ApplyDutyCycleAndSoundLength
	call Audio1_EnableChannelOutput
	pop de
	ld b, $0
	ld hl, wChannelFlags1
	add hl, bc
	bit BIT_PERFECT_PITCH, [hl] ; has toggle_perfect_pitch been used?
	jr z, .skipFrequencyInc
	inc e                       ; if yes, increment the frequency by 1
	jr nc, .skipFrequencyInc    ; Likely a mistake, because `inc` does not set flag C.
	                            ; Fortunately this does not seem to affect any notes that actually occur.
	inc d
.skipFrequencyInc
	ld hl, wChannelFrequencyLowBytes
	add hl, bc
	ld [hl], e
	call Audio1_ApplyWavePatternAndFrequency
	ret

Audio1_EnableChannelOutput:
	ld b, 0
	ld hl, Audio1_HWChannelEnableMasks
	add hl, bc
	ldh a, [rAUDTERM]
	or [hl] ; set this channel's bits
	ld d, a
	ld a, c
	cp CHAN8
	jr z, .noiseChannelOrNoSfx
	cp CHAN5
	jr nc, .skip ; if sfx channel
; If this isn't an SFX channel, try the corresponding SFX channel.
	ld hl, wChannelSoundIDs + CHAN5
	add hl, bc
	ld a, [hl]
	and a
	jr nz, .skip
.noiseChannelOrNoSfx
; If this is the SFX noise channel or a music channel whose corresponding
; SFX channel is off, apply stereo panning.
	ld a, [wStereoPanning]
	ld hl, Audio1_HWChannelEnableMasks
	add hl, bc
	and [hl]
	ld d, a
	ldh a, [rAUDTERM]
	ld hl, Audio1_HWChannelDisableMasks
	add hl, bc
	and [hl] ; reset this channel's output bits
	or d ; set this channel's output bits that enabled in [wStereoPanning]
	ld d, a
.skip
	ld a, d
	ldh [rAUDTERM], a
	ret

Audio1_ApplyDutyCycleAndSoundLength:
	ld b, 0
	ld hl, wChannelNoteDelayCounters ; use the note delay as sound length
	add hl, bc
	ld d, [hl]
	ld a, c
	cp CHAN3
	jr z, .skipDuty ; if music channel 3
	cp CHAN7
	jr z, .skipDuty ; if sfx channel 3
; include duty cycle (except on channel 3 which doesn't have it)
	ld a, d
	and $3f
	ld d, a
	ld hl, wChannelDutyCycles
	add hl, bc
	ld a, [hl]
	or d
	ld d, a
.skipDuty
	ld b, REG_DUTY_SOUND_LEN
	call Audio1_GetRegisterPointer
	ld [hl], d
	ret

Audio1_ApplyWavePatternAndFrequency:
	ld a, c
	cp CHAN3
	jr z, .channel3
	cp CHAN7
	jr nz, .notChannel3
	; fall through
.channel3
	push de
	ld de, wMusicWaveInstrument
	cp CHAN3
	jr z, .next
	ld de, wSfxWaveInstrument
.next
	ld a, [de]
	add a
	ld d, 0
	ld e, a
	ld hl, Audio1_WavePointers
	add hl, de
	ld e, [hl]
	inc hl
	ld d, [hl]
	ld hl, _AUD3WAVERAM
	ld b, AUD3WAVE_SIZE - 1
	ld a, $0 ; stop hardware channel 3
	ldh [rAUD3ENA], a
.loop
	ld a, [de]
	inc de
	ld [hli], a
	ld a, b
	dec b
	and a
	jr nz, .loop
	ld a, AUD3ENA_ON ; start hardware channel 3
	ldh [rAUD3ENA], a
	pop de
.notChannel3
	ld a, d
	or $80 ; use counter mode (i.e. disable output when the counter reaches 0)
	and $c7 ; zero the unused bits in the register
	ld d, a
	ld b, REG_FREQUENCY_LO
	call Audio1_GetRegisterPointer
	ld [hl], e ; store frequency low byte
	inc hl
	ld [hl], d ; store frequency high byte
	call Audio1_ApplyFrequencyModifier
	ret

Audio1_SetSfxTempo:
	call Audio1_IsCry
	jr nc, .notCry
	ld d, 0
	ld a, [wTempoModifier]
	add $80
	jr nc, .next
	inc d
.next
	ld [wSfxTempo + 1], a
	ld a, d
	ld [wSfxTempo], a
	jr .done
.notCry
	xor a
	ld [wSfxTempo + 1], a
	ld a, $1
	ld [wSfxTempo], a
.done
	ret

Audio1_ApplyFrequencyModifier:
	call Audio1_IsCry
	jr nc, .done
; if playing a cry, add the cry's frequency modifier
	ld a, [wFrequencyModifier]
	add e
	jr nc, .noCarry
	inc d
.noCarry
	dec hl
	ld e, a
	ld [hl], e
	inc hl
	ld [hl], d
.done
	ret

Audio1_GoBackOneCommandIfCry:
	call Audio1_IsCry
	jr nc, .done
	ld hl, wChannelCommandPointers
	ld e, c
	ld d, 0
	sla e
	rl d
	add hl, de
	ld a, [hl]
	sub 1
	ld [hl], a
	inc hl
	ld a, [hl]
	sbc 0
	ld [hl], a
	scf
	ret
.done
	scf
	ccf
	ret

Audio1_IsCry:
; Returns whether the currently playing audio is a cry in carry.
	ld a, [wChannelSoundIDs + CHAN5]
	cp CRY_SFX_START
	jr nc, .next
	jr .no
.next
	cp CRY_SFX_END
	jr z, .no
	jr c, .yes
.no
	scf
	ccf
	ret
.yes
	scf
	ret

Audio1_ApplyPitchSlide:
	ld hl, wChannelFlags1
	add hl, bc
	bit BIT_PITCH_SLIDE_DECREASING, [hl]
	jp nz, .frequencyDecreasing
; frequency increasing
	ld hl, wChannelPitchSlideCurrentFrequencyLowBytes
	add hl, bc
	ld e, [hl]
	ld hl, wChannelPitchSlideCurrentFrequencyHighBytes
	add hl, bc
	ld d, [hl]
	ld hl, wChannelPitchSlideFrequencySteps
	add hl, bc
	ld l, [hl]
	ld h, b
	add hl, de
	ld d, h
	ld e, l
	ld hl, wChannelPitchSlideCurrentFrequencyFractionalPart
	add hl, bc
	push hl
	ld hl, wChannelPitchSlideFrequencyStepsFractionalPart
	add hl, bc
	ld a, [hl]
	pop hl
	add [hl]
	ld [hl], a
	ld a, 0
	adc e
	ld e, a
	ld a, 0
	adc d
	ld d, a
	ld hl, wChannelPitchSlideTargetFrequencyHighBytes
	add hl, bc
	ld a, [hl]
	cp d
	jp c, .reachedTargetFrequency
	jr nz, .applyUpdatedFrequency
	ld hl, wChannelPitchSlideTargetFrequencyLowBytes
	add hl, bc
	ld a, [hl]
	cp e
	jp c, .reachedTargetFrequency
	jr .applyUpdatedFrequency
.frequencyDecreasing
	ld hl, wChannelPitchSlideCurrentFrequencyLowBytes
	add hl, bc
	ld a, [hl]
	ld hl, wChannelPitchSlideCurrentFrequencyHighBytes
	add hl, bc
	ld d, [hl]
	ld hl, wChannelPitchSlideFrequencySteps
	add hl, bc
	ld e, [hl]
	sub e
	ld e, a
	ld a, d
	sbc b
	ld d, a
	ld hl, wChannelPitchSlideFrequencyStepsFractionalPart
	add hl, bc
	ld a, [hl]
	add a
	ld [hl], a
	ld a, e
	sbc b
	ld e, a
	ld a, d
	sbc b
	ld d, a
	ld hl, wChannelPitchSlideTargetFrequencyHighBytes
	add hl, bc
	ld a, d
	cp [hl]
	jr c, .reachedTargetFrequency
	jr nz, .applyUpdatedFrequency
	ld hl, wChannelPitchSlideTargetFrequencyLowBytes
	add hl, bc
	ld a, e
	cp [hl]
	jr c, .reachedTargetFrequency
.applyUpdatedFrequency
	ld hl, wChannelPitchSlideCurrentFrequencyLowBytes
	add hl, bc
	ld [hl], e
	ld hl, wChannelPitchSlideCurrentFrequencyHighBytes
	add hl, bc
	ld [hl], d
	ld b, REG_FREQUENCY_LO
	call Audio1_GetRegisterPointer
	ld a, e
	ld [hli], a
	ld [hl], d
	ret
.reachedTargetFrequency
; Turn off pitch slide when the target frequency has been reached.
	ld hl, wChannelFlags1
	add hl, bc
	res BIT_PITCH_SLIDE_ON, [hl]
	res BIT_PITCH_SLIDE_DECREASING, [hl]
	ret

Audio1_InitPitchSlideVars:
	ld hl, wChannelPitchSlideCurrentFrequencyHighBytes
	add hl, bc
	ld [hl], d
	ld hl, wChannelPitchSlideCurrentFrequencyLowBytes
	add hl, bc
	ld [hl], e
	ld hl, wChannelNoteDelayCounters
	add hl, bc
	ld a, [hl]
	ld hl, wChannelPitchSlideLengthModifiers
	add hl, bc
	sub [hl]
	jr nc, .next
	ld a, 1
.next
	ld [hl], a
	ld hl, wChannelPitchSlideTargetFrequencyLowBytes
	add hl, bc
	ld a, e
	sub [hl]
	ld e, a
	ld a, d
	sbc b
	ld hl, wChannelPitchSlideTargetFrequencyHighBytes
	add hl, bc
	sub [hl]
	jr c, .targetFrequencyGreater
	ld d, a
	ld b, 0
	ld hl, wChannelFlags1
	add hl, bc
	set BIT_PITCH_SLIDE_DECREASING, [hl]
	jr .next2
.targetFrequencyGreater
; If the target frequency is greater, subtract the current frequency from
; the target frequency to get the absolute difference.
	ld hl, wChannelPitchSlideCurrentFrequencyHighBytes
	add hl, bc
	ld d, [hl]
	ld hl, wChannelPitchSlideCurrentFrequencyLowBytes
	add hl, bc
	ld e, [hl]
	ld hl, wChannelPitchSlideTargetFrequencyLowBytes
	add hl, bc
	ld a, [hl]
	sub e
	ld e, a

; Bug. Instead of borrowing from the high byte of the target frequency as it
; should, it borrows from the high byte of the current frequency instead.
; This means that the result will be 0x200 greater than it should be if the
; low byte of the current frequency is greater than the low byte of the
; target frequency.
	ld a, d
	sbc b
	ld d, a

	ld hl, wChannelPitchSlideTargetFrequencyHighBytes
	add hl, bc
	ld a, [hl]
	sub d
	ld d, a
	ld b, 0
	ld hl, wChannelFlags1
	add hl, bc
	res BIT_PITCH_SLIDE_DECREASING, [hl]

.next2
	ld hl, wChannelPitchSlideLengthModifiers
	add hl, bc
.divideLoop
	inc b
	ld a, e
	sub [hl]
	ld e, a
	jr nc, .divideLoop
	ld a, d
	and a
	jr z, .doneDividing
	dec a
	ld d, a
	jr .divideLoop
.doneDividing
	ld a, e ; a = remainder - dividend
	add [hl]
	ld d, b ; d = quotient + 1
	ld b, 0
	ld hl, wChannelPitchSlideFrequencySteps
	add hl, bc
	ld [hl], d ; store quotient + 1
	ld hl, wChannelPitchSlideFrequencyStepsFractionalPart
	add hl, bc
	ld [hl], a ; store remainder - dividend
	ld hl, wChannelPitchSlideCurrentFrequencyFractionalPart
	add hl, bc
	ld [hl], a ; store remainder - dividend
	ret

Audio1_ApplyDutyCyclePattern:
	ld b, 0
	ld hl, wChannelDutyCyclePatterns
	add hl, bc
	ld a, [hl]
	rlca
	rlca
	ld [hl], a
	and $c0
	ld d, a
	ld b, REG_DUTY_SOUND_LEN
	call Audio1_GetRegisterPointer
	ld a, [hl]
	and $3f
	or d
	ld [hl], a
	ret

Audio1_GetNextMusicByte:
	ld d, 0
	ld a, c
	add a
	ld e, a
	ld hl, wChannelCommandPointers
	add hl, de
	ld a, [hli]
	ld e, a
	ld a, [hld]
	ld d, a
	ld a, [de] ; get next music command
	inc de
	ld [hl], e ; store address of next command
	inc hl
	ld [hl], d
	ret

Audio1_GetRegisterPointer:
; hl = address of hardware sound register b for software channel c
	ld a, c
	ld hl, Audio1_HWChannelBaseAddresses
	add l
	jr nc, .noCarry
	inc h
.noCarry
	ld l, a
	ld a, [hl]
	add b
	ld l, a
	ld h, $ff
	ret

Audio1_MultiplyAdd:
; hl = l + (a * de)
	ld h, 0
.loop
	srl a
	jr nc, .skipAdd
	add hl, de
.skipAdd
	sla e
	rl d
	and a
	jr z, .done
	jr .loop
.done
	ret

Audio1_CalculateFrequency:
; return the frequency for note a, octave b in de
	ld h, 0
	ld l, a
	add hl, hl
	ld d, h
	ld e, l
	ld hl, Audio1_Pitches
	add hl, de
	ld e, [hl]
	inc hl
	ld d, [hl]
	ld a, b
.loop
	cp 7
	jr z, .done
	sra d
	rr e
	inc a
	jr .loop
.done
	ld a, 8
	add d
	ld d, a
	ret

Audio1_PlaySound::
	ld [wSoundID], a
	cp SFX_STOP_ALL_MUSIC
	jp z, .stopAllAudio
	cp MAX_SFX_ID_1
	jp z, .playSfx
	jp c, .playSfx
	cp $fe
	jr z, .playMusic
	jp nc, .playSfx

.playMusic
	xor a
	ld [wUnusedMusicByte], a
	ld [wDisableChannelOutputWhenSfxEnds], a
	ld [wMusicTempo + 1], a
	ld [wMusicWaveInstrument], a
	ld [wSfxWaveInstrument], a
	ld d, NUM_CHANNELS
	ld hl, wChannelReturnAddresses
	call .FillMem
	ld hl, wChannelCommandPointers
	call .FillMem
	ld d, NUM_MUSIC_CHANS
	ld hl, wChannelSoundIDs
	call .FillMem
	ld hl, wChannelFlags1
	call .FillMem
	ld hl, wChannelDutyCycles
	call .FillMem
	ld hl, wChannelDutyCyclePatterns
	call .FillMem
	ld hl, wChannelVibratoDelayCounters
	call .FillMem
	ld hl, wChannelVibratoExtents
	call .FillMem
	ld hl, wChannelVibratoRates
	call .FillMem
	ld hl, wChannelFrequencyLowBytes
	call .FillMem
	ld hl, wChannelVibratoDelayCounterReloadValues
	call .FillMem
	ld hl, wChannelFlags2
	call .FillMem
	ld hl, wChannelPitchSlideLengthModifiers
	call .FillMem
	ld hl, wChannelPitchSlideFrequencySteps
	call .FillMem
	ld hl, wChannelPitchSlideFrequencyStepsFractionalPart
	call .FillMem
	ld hl, wChannelPitchSlideCurrentFrequencyFractionalPart
	call .FillMem
	ld hl, wChannelPitchSlideCurrentFrequencyHighBytes
	call .FillMem
	ld hl, wChannelPitchSlideCurrentFrequencyLowBytes
	call .FillMem
	ld hl, wChannelPitchSlideTargetFrequencyHighBytes
	call .FillMem
	ld hl, wChannelPitchSlideTargetFrequencyLowBytes
	call .FillMem
	ld a, $1
	ld hl, wChannelLoopCounters
	call .FillMem
	ld hl, wChannelNoteDelayCounters
	call .FillMem
	ld hl, wChannelNoteSpeeds
	call .FillMem
	ld [wMusicTempo], a
	ld a, $ff
	ld [wStereoPanning], a
	xor a
	ldh [rAUDVOL], a
	ld a, AUD1SWEEP_DOWN
	ldh [rAUD1SWEEP], a
	ld a, 0
	ldh [rAUDTERM], a
	xor a
	ldh [rAUD3ENA], a
	ld a, AUD3ENA_ON
	ldh [rAUD3ENA], a
	ld a, $77
	ldh [rAUDVOL], a
	jp .playSoundCommon

.playSfx
	ld l, a
	ld e, a
	ld h, 0
	ld d, h
	add hl, hl
	add hl, de
	ld de, SFX_Headers_1
	add hl, de
	ld a, h
	ld [wSfxHeaderPointer], a
	ld a, l
	ld [wSfxHeaderPointer + 1], a
	ld a, [hl]
	and $c0
	rlca
	rlca
	ld c, a
.sfxChannelLoop
	ld d, c
	ld a, c
	add a
	add c
	ld c, a
	ld b, 0
	ld a, [wSfxHeaderPointer]
	ld h, a
	ld a, [wSfxHeaderPointer + 1]
	ld l, a
	add hl, bc
	ld c, d
	ld a, [hl]
	and $f
	ld e, a ; software channel ID
	ld d, 0
	ld hl, wChannelSoundIDs
	add hl, de
	ld a, [hl]
	and a
	jr z, .playChannel
	ld a, e
	cp CHAN8
	jr nz, .notNoiseChannel
	ld a, [wSoundID]
	cp NOISE_INSTRUMENTS_END
	jr nc, .notNoiseInstrument
	ret
.notNoiseInstrument
	ld a, [hl]
	cp NOISE_INSTRUMENTS_END
	jr z, .playChannel
	jr c, .playChannel
.notNoiseChannel
	ld a, [wSoundID]
	cp [hl]
	jr z, .playChannel
	jr c, .playChannel
	ret
.playChannel
	xor a
	push de
	ld h, d
	ld l, e
	add hl, hl
	ld d, h
	ld e, l
	ld hl, wChannelReturnAddresses
	add hl, de
	ld [hli], a
	ld [hl], a
	ld hl, wChannelCommandPointers
	add hl, de
	ld [hli], a
	ld [hl], a
	pop de
	ld hl, wChannelSoundIDs
	add hl, de
	ld [hl], a
	ld hl, wChannelFlags1
	add hl, de
	ld [hl], a
	ld hl, wChannelDutyCycles
	add hl, de
	ld [hl], a
	ld hl, wChannelDutyCyclePatterns
	add hl, de
	ld [hl], a
	ld hl, wChannelVibratoDelayCounters
	add hl, de
	ld [hl], a
	ld hl, wChannelVibratoExtents
	add hl, de
	ld [hl], a
	ld hl, wChannelVibratoRates
	add hl, de
	ld [hl], a
	ld hl, wChannelFrequencyLowBytes
	add hl, de
	ld [hl], a
	ld hl, wChannelVibratoDelayCounterReloadValues
	add hl, de
	ld [hl], a
	ld hl, wChannelPitchSlideLengthModifiers
	add hl, de
	ld [hl], a
	ld hl, wChannelPitchSlideFrequencySteps
	add hl, de
	ld [hl], a
	ld hl, wChannelPitchSlideFrequencyStepsFractionalPart
	add hl, de
	ld [hl], a
	ld hl, wChannelPitchSlideCurrentFrequencyFractionalPart
	add hl, de
	ld [hl], a
	ld hl, wChannelPitchSlideCurrentFrequencyHighBytes
	add hl, de
	ld [hl], a
	ld hl, wChannelPitchSlideCurrentFrequencyLowBytes
	add hl, de
	ld [hl], a
	ld hl, wChannelPitchSlideTargetFrequencyHighBytes
	add hl, de
	ld [hl], a
	ld hl, wChannelPitchSlideTargetFrequencyLowBytes
	add hl, de
	ld [hl], a
	ld hl, wChannelFlags2
	add hl, de
	ld [hl], a
	ld a, $1
	ld hl, wChannelLoopCounters
	add hl, de
	ld [hl], a
	ld hl, wChannelNoteDelayCounters
	add hl, de
	ld [hl], a
	ld hl, wChannelNoteSpeeds
	add hl, de
	ld [hl], a
	ld a, e
	cp CHAN5
	jr nz, .skipSweepDisable
	ld a, AUD1SWEEP_DOWN
	ldh [rAUD1SWEEP], a ; sweep off
.skipSweepDisable
	ld a, c
	and a
	jp z, .playSoundCommon
	dec c
	jp .sfxChannelLoop

.stopAllAudio
	ld a, AUDENA_ON
	ldh [rAUDENA], a ; sound hardware on
	ldh [rAUD3ENA], a ; wave playback on
	xor a
	ldh [rAUDTERM], a ; no sound output
	ldh [rAUD3LEVEL], a ; mute channel 3 (wave channel)
	ld a, AUD1SWEEP_DOWN
	ldh [rAUD1SWEEP], a ; sweep off
	ldh [rAUD1ENV], a ; mute channel 1 (pulse channel 1)
	ldh [rAUD2ENV], a ; mute channel 2 (pulse channel 2)
	ldh [rAUD4ENV], a ; mute channel 4 (noise channel)
	ld a, AUD1HIGH_LENGTH_ON
	ldh [rAUD1HIGH], a ; counter mode
	ldh [rAUD2HIGH], a
	ldh [rAUD4GO], a
	ld a, $77
	ldh [rAUDVOL], a ; full volume
	xor a
	ld [wUnusedMusicByte], a
	ld [wDisableChannelOutputWhenSfxEnds], a
	ld [wMuteAudioAndPauseMusic], a
	ld [wMusicTempo + 1], a
	ld [wSfxTempo + 1], a
	ld [wMusicWaveInstrument], a
	ld [wSfxWaveInstrument], a
	ld d, $a0
	ld hl, wChannelCommandPointers
	call .FillMem
	ld a, $1
	ld d, $18
	ld hl, wChannelNoteDelayCounters
	call .FillMem
	ld [wMusicTempo], a
	ld [wSfxTempo], a
	ld a, $ff
	ld [wStereoPanning], a
	ret

; fills d bytes at hl with a
.FillMem
	ld b, d
.loop
	ld [hli], a
	dec b
	jr nz, .loop
	ret

.playSoundCommon
	ld a, [wSoundID]
	ld l, a
	ld e, a
	ld h, 0
	ld d, h
	add hl, hl
	add hl, de
	ld de, SFX_Headers_1
	add hl, de
	ld e, l
	ld d, h
	ld hl, wChannelCommandPointers
	ld a, [de] ; get channel number
	ld b, a
	rlca
	rlca
	and $3
	ld c, a
	ld a, b
	and $f
	ld b, c
	inc b
	inc de
	ld c, 0
.commandPointerLoop
	cp c
	jr z, .next
	inc c
	inc hl
	inc hl
	jr .commandPointerLoop
.next
	push hl
	push bc
	push af
	ld b, 0
	ld c, a
	ld hl, wChannelSoundIDs
	add hl, bc
	ld a, [wSoundID]
	ld [hl], a
	pop af
	cp CHAN4
	jr c, .skipSettingFlag
	ld hl, wChannelFlags1
	add hl, bc
	set BIT_NOISE_OR_SFX, [hl]
.skipSettingFlag
	pop bc
	pop hl
	ld a, [de] ; get channel pointer
	ld [hli], a
	inc de
	ld a, [de]
	ld [hli], a
	inc de
	inc c
	dec b
	ld a, b
	and a
	ld a, [de]
	inc de
	jr nz, .commandPointerLoop
	ld a, [wSoundID]
	cp CRY_SFX_START
	jr nc, .maybeCry
	jr .done
.maybeCry
	ld a, [wSoundID]
	cp CRY_SFX_END
	jr z, .done
	jr c, .cry
	jr .done
.cry
	ld hl, wChannelSoundIDs + CHAN5
	ld [hli], a
	ld [hli], a
	ld [hli], a
	ld [hl], a
	ld hl, wChannelCommandPointers + CHAN7 * 2 ; sfx wave channel pointer
	ld de, Audio1_CryRet
	ld [hl], e
	inc hl
	ld [hl], d ; overwrite pointer to point to sound_ret
	ld a, [wSavedVolume]
	and a
	jr nz, .done
	ldh a, [rAUDVOL]
	ld [wSavedVolume], a
	ld a, $77
	ldh [rAUDVOL], a ; full volume
.done
	ret

Audio1_CryRet:
	sound_ret

Audio1_HWChannelBaseAddresses:
; the low bytes of each HW channel's base address
	db HW_CH1_BASE, HW_CH2_BASE, HW_CH3_BASE, HW_CH4_BASE ; channels 0-3
	db HW_CH1_BASE, HW_CH2_BASE, HW_CH3_BASE, HW_CH4_BASE ; channels 4-7

Audio1_HWChannelDisableMasks:
	db HW_CH1_DISABLE_MASK, HW_CH2_DISABLE_MASK, HW_CH3_DISABLE_MASK, HW_CH4_DISABLE_MASK ; channels 0-3
	db HW_CH1_DISABLE_MASK, HW_CH2_DISABLE_MASK, HW_CH3_DISABLE_MASK, HW_CH4_DISABLE_MASK ; channels 4-7

Audio1_HWChannelEnableMasks:
	db HW_CH1_ENABLE_MASK, HW_CH2_ENABLE_MASK, HW_CH3_ENABLE_MASK, HW_CH4_ENABLE_MASK ; channels 0-3
	db HW_CH1_ENABLE_MASK, HW_CH2_ENABLE_MASK, HW_CH3_ENABLE_MASK, HW_CH4_ENABLE_MASK ; channels 4-7

Audio1_Pitches:
INCLUDE "audio/notes.asm"