river-raid: Routine at 6C31

6C31: Play bonus life sound effect

Generates a rising pitch sound effect when player earns an extra life. Called once per interrupt while CONTROLS_BIT_BONUS_LIFE is set. The sound plays over 64 interrupts (~1.28 seconds). Counter increments from 0 to 64 over successive interrupts Pitch = ($40 - counter) >> 3, giving values 7→0 as counter increases Lower pitch values = higher frequency, so sound rises in pitch Calls ROM BEEPER routine at $03B5 with duration L=$FF, repeat DE=$0001
do_bonus_life	6C31	LD A,($6C30)	Increment counter and check if reached $40 (64). If so, sound is complete.
	6C34	INC A
	6C35	LD ($6C30),A
	6C38	CP $40	Check if counter reached BONUS_LIFE_SOUND_TICKS. If done, finish sound sequence.
	6C3A	JP Z,bonus_life_sound_done
	6C3D	LD B,A	Calculate pitch: pitch = BONUS_LIFE_SOUND_TICKS - counter.
	6C3E	LD A,$40
	6C40	SUB B
	6C41	LD L,$FF	Set up BEEPER parameters: H = pitch >> 3 (range 7-0), L = $FF (duration).
	6C43	LD H,A
	6C44	SRL H
	6C46	SRL H
	6C48	SRL H
	6C4A	LD DE,$0001	Call ROM BEEPER at $03B5 with DE=$0001 (one iteration). Disable interrupts after.
	6C4D	CALL $03B5
	6C50	DI
	6C51	RET