Knight Lore: Routine at D50E

Used by the routine at end_of_frame.

Called once a frame. The half-row $7E is B, N, M, SYMBOL SHIFT and SPACE, and read_port returns SPACE as bit 0. Only SPACE on its own pauses: with any other key of that half-row held as well the routine returns. Why that matters has not been worked out.

The pause itself is a busy wait inside this routine: nothing moves, nothing is drawn and the frame counter stops until SPACE is pressed and let go again. toggle_audio_hw_x24 sounds on the way in and on the way out.

Used by the routine at end_of_frame. Called once a frame. The half-row $7E is B, N, M, SYMBOL SHIFT and SPACE, and read_port returns SPACE as bit 0. Only SPACE on its own pauses: with any other key of that half-row held as well the routine returns. Why that matters has not been worked out. The pause itself is a busy wait inside this routine: nothing moves, nothing is drawn and the frame counter stops until SPACE is pressed and let go again. toggle_audio_hw_x24 sounds on the way in and on the way out.
handle_pause	D50E	LD A,$7E	SPACE not pressed: carry on
	D510	CALL read_port
	D513	BIT 0,A
	D515	RET Z
	D516	AND $1E	another key of the half-row is held too: not a pause
	D518	RET NZ