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47 lines
1.3 KiB
ArmAsm
47 lines
1.3 KiB
ArmAsm
; Oliver Schmidt
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; comp.sys.apple2.programmer
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; Call with joystick number (0 or 1) in A.
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; Results are stored in value0 and value1.
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; UPPER_THRESHOLD is the paddle value you want to consider as "right enough" /
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; "down enough".
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UPPER_THRESHOLD = 128
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;PTRIG = $c070
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PADDL1 = $C065
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handle_joystick:
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lda #0
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; Read both paddles simultaneously
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asl ; Joystick number -> paddle number
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tax
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ldy #$00
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sty value0
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sty value1
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lda PTRIG ; Trigger paddles
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loop: lda PADDL0,x ; Read paddle (0 or 2)
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bmi set0 ; Cycles: 2 3
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nop ; Cycles: 2
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bpl nop0 ; Cycles: 3
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set0: sty value0 ; Cycles: 4
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nop0: ; - -
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; Cycles: 7 7
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lda PADDL1,x ; Read paddle (1 or 3)
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bmi set1 ; Cycles: 2 3
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nop ; Cycles: 2
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bpl nop1 ; Cycles: 3
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set1: sty value1 ; Cycles: 4
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nop1: ; - -
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; Cycles: 7 7
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iny
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cpy #UPPER_THRESHOLD+1
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bne loop
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rts
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value0: .byte $00
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value1: .byte $00
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