Alien 8: Routine at CE22

Used by the routine at OBJECT_DONE.

Called once a turn by the main loop (OBJECT_DONE). READ_KEYS is given $7E, which selects two half-rows at once -- SPACE to B, and CAPS SHIFT to V -- read with a key pressed as a set bit; SPACE and CAPS SHIFT share bit 0, so either on its own pauses. A beep (PAUSE_BEEP), a wait for the key to be let go, then for a press and a release, and a beep again.

The pause is a busy wait with interrupts off: the game has no EI anywhere, so nothing runs while it waits. Pentagram's pause turns interrupts on while it waits; Knight Lore's and this one do not.

Used by the routine at OBJECT_DONE. Called once a turn by the main loop (OBJECT_DONE). READ_KEYS is given $7E, which selects two half-rows at once -- SPACE to B, and CAPS SHIFT to V -- read with a key pressed as a set bit; SPACE and CAPS SHIFT share bit 0, so either on its own pauses. A beep (PAUSE_BEEP), a wait for the key to be let go, then for a press and a release, and a beep again. The pause is a busy wait with interrupts off: the game has no EI anywhere, so nothing runs while it waits. Pentagram's pause turns interrupts on while it waits; Knight Lore's and this one do not.
HANDLE_PAUSE	CE22	LD A,$7E	SPACE not pressed: no pause
	CE24	CALL READ_KEYS
	CE27	BIT 0,A
	CE29	RET Z
	CE2A	AND $1E	Another key of the half-row with it: no pause
	CE2C	RET NZ	Another key of the half-row with it: no pause
HANDLE_PAUSE_0	CE2D	LD A,$7E	Wait for it to be let go
	CE2F	CALL READ_KEYS
	CE32	BIT 0,A
	CE34	JR NZ,HANDLE_PAUSE_0
	CE36	CALL PAUSE_BEEP	A beep
HANDLE_PAUSE_1	CE39	LD A,$7E	Wait for a press
	CE3B	CALL READ_KEYS
	CE3E	BIT 0,A
	CE40	JR Z,HANDLE_PAUSE_1
HANDLE_PAUSE_2	CE42	LD A,$7E	And for it to be let go
	CE44	CALL READ_KEYS
	CE47	BIT 0,A
	CE49	JR NZ,HANDLE_PAUSE_2
	CE4B	JP PAUSE_BEEP	A beep, and back to the game