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