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30 lines
885 B
PHP
30 lines
885 B
PHP
;
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; Callback routine called from the IRQ handler after the ROM IRQ handler
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; had been run.
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;
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; Christian Groessler, 24.04.2014
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;
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; Check if there was button/joystick activity before and/or after the ROM handler.
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; If there was activity, discard the key presses since they are most
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; probably "phantom" key presses.
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callback:
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ldx old_key_count
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cpx KEY_COUNT
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beq @nokey
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lda OLD_BUTTONS ; keypress before?
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bne @discard_key ; yes, discard key
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lda #$7F
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sta CIA1_PRA
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lda CIA1_PRB ; Read joystick #0
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and #$1F
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eor #$1F ; keypress after
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beq @nokey ; no, probably a real key press
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@discard_key:
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stx KEY_COUNT ; set old keyboard buffer fill level
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@nokey: rts
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