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Music_DoLowHealthAlarm::
ld a, [wLowHealthAlarm]
cp $ff
jr z, .disableAlarm
bit 7, a ;alarm enabled?
ret z ;nope
and $7f ;low 7 bits are the timer.
jr nz, .asm_21383 ;if timer > 0, play low tone.
call .playToneHi
ld a, 30 ;keep this tone for 30 frames.
jr .asm_21395 ;reset the timer.
.asm_21383
cp 20
jr nz, .asm_2138a ;if timer == 20,
call .playToneLo ;actually set the sound registers.
.asm_2138a
ld a, $86
ld [wChannelSoundIDs + Ch5], a ;disable sound channel?
ld a, [wLowHealthAlarm]
and $7f ;decrement alarm timer.
dec a
.asm_21395
; reset the timer and enable flag.
set 7, a
ld [wLowHealthAlarm], a
ret
.disableAlarm
xor a
ld [wLowHealthAlarm], a ;disable alarm
ld [wChannelSoundIDs + Ch5], a ;re-enable sound channel?
ld de, .toneDataSilence
jr .playTone
;update the sound registers to change the frequency.
;the tone set here stays until we change it.
.playToneHi
ld de, .toneDataHi
jr .playTone
.playToneLo
ld de, .toneDataLo
;update sound channel 1 to play the alarm, overriding all other sounds.
.playTone
ld hl, rNR10 ;channel 1 sound register
ld c, $5
xor a
.copyLoop
ld [hli], a
ld a, [de]
inc de
dec c
jr nz, .copyLoop
ret
;bytes to write to sound channel 1 registers for health alarm.
;starting at FF11 (FF10 is always zeroed), so these bytes are:
;length, envelope, freq lo, freq hi
.toneDataHi
db $A0,$E2,$50,$87
.toneDataLo
db $B0,$E2,$EE,$86
;written to stop the alarm
.toneDataSilence
db $00,$00,$00,$80
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