4cade/src/hw.joystick.a

;------------------------------------------------------------------------------
; 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
;------------------------------------------------------------------------------
; Fastchip firmware 0.4b-compatibility fix by Frank M. (0.5b seems unaffected)
;------------------------------------------------------------------------------
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
++
         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