emailler/drivers/c64_input.s

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.export check_for_abort_key
.export abort_key
.exportzp abort_key_default = $3f
.exportzp abort_key_disable = $ff
.data
abort_key: .byte $3f ; RUN/STOP
.code
; check whether the abort key is being pressed
; inputs: none
; outputs: sec if abort key pressed, clear otherwise
check_for_abort_key:
lda $cb ; current key pressed
cmp abort_key
bne no_key
@flush_loop:
ldy #$ff
jsr $f142 ; not officially documented - where F13E (GETIN) falls through to if device # is 0 (KEYBD)
cpy #$ff ; Y gets modified iff there's a character available - this approach allows to read ^@ as 0
bne @flush_loop
lda $cb ; current key pressed
cmp abort_key
beq @flush_loop
sec
rts
no_key:
clc
rts
; -- LICENSE FOR c64_input.s --
; The contents of this file are subject to the Mozilla Public License
; Version 1.1 (the "License"); you may not use this file except in
; compliance with the License. You may obtain a copy of the License at
; http://www.mozilla.org/MPL/
;
; Software distributed under the License is distributed on an "AS IS"
; basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
; License for the specific language governing rights and limitations
; under the License.
;
; The Original Code is ip65.
;
; The Initial Developer of the Original Code is Jonno Downes,
; jonno@jamtronix.com.
; Portions created by the Initial Developer are Copyright (C) 2009
; Jonno Downes. All Rights Reserved.
; -- LICENSE END --