4cade/src/hw.joystick.a

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;------------------------------------------------------------------------------
; HasJoystick
; Checks whether computer has joystick connected
;
; in: none
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; out: C set if joystick found
; C clear if no joystick found
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; 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
;------------------------------------------------------------------------------
; Fastchip firmware 0.4b-compatibility fix by Frank M. (0.5b seems unaffected)
;------------------------------------------------------------------------------
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HasJoystick
lda $FBB3
cmp #$06
bne ++
lda $FBC0
cmp #$E0
beq + ; test for Fastchip on enhanced //e
cmp #$EA
beq + ; test for Fastchip on non-enhanced //e
jmp ++
+ ; FASTChip
fc_lock = $C06A
fc_enable = $C06B
fc_config = $C06E
fc_data = $C06F
FC_UNLOCK = $6A ; write 4 times
FC_LOCK = $A6
FC_SPKR = 2 ; speaker delay register
FC_HIFI = 4 ; set to 'HIFI'
FC_JOY = 3 ; joystick delay register
FC_LONG = 2 ; set to 'LONG'
lda #FC_UNLOCK
sta fc_lock
sta fc_lock
sta fc_lock
sta fc_lock
sta fc_enable
lda fc_enable ; 00 if no fastchip
cmp #$80 ; 80 if Fastchip normal
bne ++ ; A0 if Fastchip disabled
lda #FC_JOY ; change Fastchip joystick delay setting to 'LONG'
sta fc_config ; (improves joystick detection)
lda #FC_LONG
sta fc_data
lda #FC_SPKR ; change Fastchip speaker delay setting to 'HIFI'
sta fc_config ; (improves sound on most games)
lda #FC_HIFI
sta fc_data
lda #FC_LOCK ; (settings revert on power cycle)
sta fc_lock
++
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lda #0
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sta @joyX
sta @joyY
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lda $C070 ; reset analog input timers
@loop ldx #1
@1 lda $C064,x ; check timer input
bpl @beat
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inc @joyX,x ; still high, increment counter
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@nextpdl dex
bpl @1
lda $C064
ora $C065
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bpl @yes ; both inputs low, we're done
lda @joyX
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
@beat nop
bpl @nextpdl ; kill time
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@joyX !byte 0
@joyY !byte 0