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cc65/libsrc/lynx/kbhit.s

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;
; Karri Kaksonen, 2004-11-01
;
; unsigned char kbhit (void);
;
.export _kbhit
.export KBBUF
.import return0, return1
; --------------------------------------------------------------------------
; The Atari Lynx has a very small keyboard - only 3 keys
; Opt1, Opt2 and Pause.
; But the designers have decided that pressing Pause and Opt1 at the
; same time means Restart and pressing Pause and Opt2 means Flip screen.
; For "easter egg" use I have also included all three keys pressed '?'
; and Opt1 + Opt2 pressed '3'.
; So the keyboard returns '1', '2', '3', 'P', 'R', 'F' or '?'.
.data
KBBUF: .byte 0
DEBOUNCE: .byte 0 ; Contains char until key is freed
.code
_kbhit:
lda $FCB1 ; Read the Pause key
and #1
bne @L4
lda $FCB0 ; No Pause pressed
and #$0c
bne @L1
stz DEBOUNCE ; No keys pressed at all
lda KBBUF ; But we may have some old key in the buffer
bne @L9
jmp return0 ; No key has been pressed
@L1:
cmp #$0c
bne @L2
ldx #'3' ; Opt 1 + Opt 2 pressed
bra @L8
@L2:
cmp #$08
bne @L3
ldx #'1' ; Opt 1 pressed
bra @L8
@L3:
ldx #'2' ; Opt 2 pressed
bra @L8
@L4:
lda $FCB0
and #$0c
bne @L5
ldx #'P' ; Pause pressed
bra @L8
@L5:
cmp #$0c
bne @L6
ldx #'?' ; Opt 1 + Opt 2 + Pause pressed
bra @L8
@L6:
cmp #$08
bne @L7
ldx #'R' ; Restart pressed
bra @L8
@L7:
ldx #'F' ; Flip pressed
@L8:
lda KBBUF
bne @L10
lda DEBOUNCE
beq @L10
jmp return0 ; Return no key pressed until keys are released
@L10:
stx KBBUF
sta DEBOUNCE
@L9: jmp return1