4cade/src/hw.joystick.a
2019-01-13 18:55:40 -05:00

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;------------------------------------------------------------------------------
; HasJoystick
; Checks whether computer has joystick connected
;
; in: none
; out: C set if joystick found
; C clear if no joystick found
; other flags clobbered
; A,X clobbered
; Y preserved
;
; adapted from "Prince of Persia" by Jordan Mechner
; (c) 1989 Broderbund Software
; https://github.com/jmechner/Prince-of-Persia-Apple-II/blob/master/01%20POP%20Source/Source/GRAFIX.S#L1225
;------------------------------------------------------------------------------
HasJoystick
lda #0
sta @joyX
sta @joyY
lda $C070 ; reset analog input timers
@loop ldx #1
@1 lda $C064,x ; check timer input
bpl @beat
inc @joyX,x ; still high, increment counter
@nextpdl dex
bpl @1
lda $C064
ora $C065
bpl @yes ; both inputs low, we're done
lda @joyX
ora @joyY
bpl @loop ; do it again
@no clc
+HIDE_NEXT_BYTE
@yes sec
rts
@beat nop
bpl @nextpdl ; kill time
@joyX !byte 0
@joyY !byte 0