river-raid: Routine at 7ACD

7ACD: Wait until the user chooses a valid control type or switch to the overview mode on timeout.


controls_input	7ACD	LD HL,($7802)	Decrease timer
	7AD0	DEC HL
	7AD1	LD ($7802),HL
	7AD4	LD A,H	Check if the time is up
	7AD5	OR L
	7AD6	JP Z,switch_to_overview_mode
	7AD9	LD A,($5C08)
	7ADC	CALL $02BF	Scan keyboard
	7ADF	EI	Scan keyboard
	7AE0	SUB $31	Subtract "1" from the pressed key ASCII code, mapping "1" to 0, "2" to 1, etc.
	7AE2	LD ($7800),A
	7AE5	AND $FC	Validate the pressed key by making sure that none of the bits older than the first two are set, effectively allowing values 0 through 3.
	7AE7	CP $00
	7AE9	JR NZ,controls_input	Repeat if a valid key was not pressed.
	7AEB	LD A,$FF
game_mode_print	7AED	LD B,$00	Initialize delay counter.
controls_input_delay_loop	7AEF	DJNZ controls_input_delay_loop	Delay loop (purpose unclear).
	7AF1	DEC A
	7AF2	JR NZ,game_mode_print
	7AF4	LD D,$07	PAPER BLACK; INK WHITE
	7AF6	CALL clear_screen
	7AF9	LD DE,$792A	Print game mode dialog
	7AFC	LD BC,$0104
	7AFF	CALL $203C
	7B02	LD A,$0D
	7B04	LD ($5C08),A