dos33fsprogs/games/duke/joystick.s

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2020-11-28 05:51:57 +00:00
; Oliver Schmidt
; comp.sys.apple2.programmer
; Call with joystick number (0 or 1) in A.
; Results are stored in value0 and value1.
; UPPER_THRESHOLD is the paddle value you want to consider as "right enough" /
; "down enough".
UPPER_THRESHOLD = 128
;PTRIG = $c070
PADDL1 = $C065
handle_joystick:
lda #0
; Read both paddles simultaneously
asl ; Joystick number -> paddle number
tax
ldy #$00
sty value0
sty value1
lda PTRIG ; Trigger paddles
loop: lda PADDL0,x ; Read paddle (0 or 2)
bmi set0 ; Cycles: 2 3
nop ; Cycles: 2
bpl nop0 ; Cycles: 3
set0: sty value0 ; Cycles: 4
nop0: ; - -
; Cycles: 7 7
lda PADDL1,x ; Read paddle (1 or 3)
bmi set1 ; Cycles: 2 3
nop ; Cycles: 2
bpl nop1 ; Cycles: 3
set1: sty value1 ; Cycles: 4
nop1: ; - -
; Cycles: 7 7
iny
cpy #UPPER_THRESHOLD+1
bne loop
rts
value0: .byte $00
value1: .byte $00