Everyone's A Wally: Routine at B482

B482: Play the next note of the theme tune and get a keypress

Used by the routine at 80E5.
B482	LD HL,($B4E7)	Point HL towards the next note in the tune.
B485	LD A,(HL)	Is the next byte zero?
B486	OR A	Is the next byte zero?
B487	JR NZ,$B494	Jump forward if it isn't.
B489	LD A,$01	Set tune back to index 1.
B48B	LD ($B55F),A	Set tune back to index 1.
B48E	LD A,$FF	Set no keys pressed and return.
B490	LD ($B4E9),A
B493	RET
There is more of the tune to play, so do it. First, work out if the type of sound wave needs changing.
B494	INC HL	Point HL at the next note.
B495	CP $FE	Is it a control character FE?
B497	JR NZ,$B4A2	Jump forward if it isn't.
B499	XOR A	Switch to sawtooth wave.
B49A	LD ($B4EA),A	Switch to sawtooth wave.
B49D	LD ($B4E7),HL	Set the next address of the tune to play. (B4E7)
B4A0	JR $B482	Jump forward to play the note.
B4A2	CP $FF	Is it a control character FF?
B4A4	JR NZ,$B4AA	Jump forward if not.
B4A6	LD A,$01	Switch to square wave and jump back to set this.
B4A8	JR $B49A	Switch to square wave and jump back to set this.
Now play the note.
B4AA	PUSH AF	Store AF.
B4AB	LD A,(HL)	Get the current note.
B4AC	INC HL	Point HL at the next note to play.
B4AD	LD ($B4E7),HL	Point HL at the next note to play.
B4B0	OR A	Is it zero?
B4B1	JR Z,$B4DB	If so, jump forward.
B4B3	LD L,A	Put the note in HL.
B4B4	LD H,$00	Put the note in HL.
B4B6	ADD HL,HL	Double it to get a word offset.
B4B7	LD DE,$B537	Add the base address for the note frequencies. (B537)
B4BA	ADD HL,DE	Add the base address for the note frequencies. (B537)
B4BB	LD C,(HL)	Get the frequency and put it in BC.
B4BC	LD B,$00	Get the frequency and put it in BC.
B4BE	INC HL	Get the length and put it in DE.
B4BF	LD E,(HL)
B4C0	LD D,B
B4C1	POP AF	Restore AF.
B4C2	LD HL,$0000	Multiply DE with the note value to get the length.
B4C5	ADD HL,DE
B4C6	DEC A
B4C7	JR NZ,$B4C5
B4C9	EX DE,HL	Swap DE and HL.
B4CA	CALL $B505	Play the note.
B4CD	LD A,($B4E9)	Was a key pressed?
B4D0	CP $FF	Was a key pressed?
B4D2	RET NZ	Return if it was.
B4D3	LD BC,$0320	Pause and get a keypress.
B4D6	CALL $B4EB	Pause and get a keypress.
B4D9	JR $B482	Jump back and play more of the tune.
B4DB	LD BC,$19C8
B4DE	POP AF	Restore AF.
B4DF	CALL $B4EB	Pause and get a keypress.
B4E2	DEC A	Was a key pressed? Loop while there was.
B4E3	JR NZ,$B4DF	Was a key pressed? Loop while there was.
B4E5	JR $B4D3	Otherwise jump back to play more of the tune.