Tranz Am: Routine at 611B

Used by the routine at HandlerPlayer.

Plays the next step of the sound made when a cup is collected or the car is refuelled. This is called every frame but only makes a sound on every other frame. The step counter is held at SoundCounter. For the refuel sound it counts down from 07 and bit 7 is clear; each step has a higher pitch than the one before. For the cup sound it starts at 87 (bit 7 set) and each step has a lower pitch than the one before. Each step plays 20 square waves using PlaySquareWave, and there are six of them. The cup sound:

The refuel sound:

Used by the routine at HandlerPlayer. Plays the next step of the sound made when a cup is collected or the car is refuelled. This is called every frame but only makes a sound on every other frame. The step counter is held at SoundCounter. For the refuel sound it counts down from 07 and bit 7 is clear; each step has a higher pitch than the one before. For the cup sound it starts at 87 (bit 7 set) and each step has a lower pitch than the one before. Each step plays 20 square waves using PlaySquareWave, and there are six of them. The cup sound: The refuel sound:
SoundsCupRefuel	611B	LD A,($5E29)	Fetch the game timer from GameTimer.
	611E	AND %00000001	Keep only bit 0.
	6120	RET NZ	Return on every other frame.
	6121	LD HL,$5E46	Point HL at the step counter (SoundCounter).
	6124	LD A,(HL)	Fetch the step counter.
	6125	BIT 7,A	Jump to SoundsCup if bit 7 is set, as that is the cup sound.
	6127	JR NZ,SoundsCup
	6129	AND A	Return if the step counter is zero, as there is no sound to play.
	612A	RET Z
	612B	DEC A	Decrease the step counter by one.
	612C	LD (HL),A	Write the new step counter back to SoundCounter.
	612D	RET Z	Return if the step counter has reached zero, as the sound is over.
Work out the period of the waves from the step counter.
SoundsRefuel	612E	RLCA	Multiply the step counter by 04 by rotating it left twice.
	612F	RLCA	Multiply the step counter by 04 by rotating it left twice.
	6130	AND %00011100	Keep only bits 2-4.
	6132	OR %00100000	Set bit 5.
	6134	LD D,A	Set the period of the waves.
	6135	LD C,$20	Set the wave counter to 20.
SoundsCupRefuel_Loop	6137	CALL PlaySquareWave	Play a square wave using PlaySquareWave.
	613A	DEC C	Decrease the wave counter by one and loop back to SoundsCupRefuel_Loop until all 20 waves have been played.
	613B	JR NZ,SoundsCupRefuel_Loop
	613D	RET	Return.
The cup sound keeps bit 7 set in the step counter, and inverts the step so that the pitch falls rather than rises.
SoundsCup	613E	AND %01111111	Keep only the step counter (bits 0-6).
	6140	RET Z	Return if the step counter is zero, as the sound is over.
	6141	DEC A	Decrease the step counter by one.
	6142	OR %10000000	Set bit 7 so that the sound stays the cup sound.
	6144	LD (HL),A	Write the new step counter back to SoundCounter.
	6145	AND %01111111	Keep only the step counter (bits 0-6).
	6147	RET Z	Return if the step counter has reached zero.
	6148	CPL	Flip the bits, so that the pitch falls with each step.
	6149	JR SoundsRefuel	Jump to SoundsRefuel.