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