Knight Tyme (48k): Routine at 54575

54575: If key-press was enqueued then return index of last key pressed, else wait for key-press and return index

Used by the routines at 31468 and 54647.

Output
A	Index of key pressed

The operand of the instruction at 54575 represents an enqueued key-press. This is modified by the instructions at 54593 and 54656.

54575

LD A,0

Load A with enqueued key index...

54577

OR A

...and if not zero...

54578

JR NZ,54584

...then skip ahead to 54584

54580

XOR A

Clear last pressed key...

54581

LD (23560),A

...

54584

HALT

Wait for interrupt

54585

LD A,(23560)

Load last pressed key into A...

54588

OR A

...and if this is zero (i.e. no key pressed)...

54589

JR Z,54584

...then loop back to 54584

54591

EX AF,AF'

Switch AF and AF'

54592

XOR A

Set enqueued key index to zero...

54593

LD (54576),A

...

54596

EX AF,AF'

Switch AF and AF'

54597

RET

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