cc65/libsrc/apple2/apple2-stdjoy.s

;
; Standard joystick driver for the Apple ][. May be used multiple times
; when statically linked to the application.
;
; Ullrich von Bassewitz, 2003-05-02
; Oliver Schmidt, 2008-02-25
; Using the readjoy code from Stefan Haubenthal
;

 	.include 	"zeropage.inc"

      	.include 	"joy-kernel.inc"
        .include        "joy-error.inc"
        .include        "apple2.inc"

; ------------------------------------------------------------------------

; Constants

THRESHOLD =	20	; Deviation from center triggering movement

; ------------------------------------------------------------------------

; ROM entry points

PREAD  	:=  	$FB1E	; Read paddle in X, return AD conv. value in Y

; ------------------------------------------------------------------------

; Header. Includes jump table.

	.segment        "JUMPTABLE"

; Driver signature

        .byte   $6A, $6F, $79	; "joy"
        .byte   JOY_API_VERSION	; Driver API version number

; Button state masks (8 values)

        .byte   $10
        .byte   $20
        .byte   $04
        .byte   $08
        .byte   $40
        .byte   $80
        .byte   $00             ; Future expansion
        .byte   $00             ; Future expansion

; Jump table

        .addr   INSTALL
        .addr   UNINSTALL
        .addr   COUNT
        .addr   READJOY
        .addr   0               ; IRQ not used

; ------------------------------------------------------------------------

	.code

; INSTALL routine. Is called after the driver is loaded into memory. If
; possible, check if the hardware is present and determine the amount of
; memory available.
; Must return an JOY_ERR_xx code in a/x.
INSTALL:
        lda     #<JOY_ERR_OK
        ldx     #>JOY_ERR_OK
	; Fall through

; UNINSTALL routine. Is called before the driver is removed from memory.
; Can do cleanup or whatever. Must not return anything.
UNINSTALL:
        rts

; COUNT: Return the total number of available joysticks in a/x.
COUNT:
        lda     #$02		; Number of joysticks we support
        ldx     #$00
        rts

; READ: Read a particular joystick passed in A.
READJOY:
        bit	$C082		; Switch in ROM
	and    	#$01            ; Restrict joystick number

	; Read horizontal paddle
	asl			; Joystick number -> paddle number
	tax	     		; Set paddle number (0, 2)
        jsr     PREAD           ; Read paddle value
        lda	#$00		; 0 0 0 0 0 0 0 0
        cpy     #127 - THRESHOLD
        ror			; !LEFT 0 0 0 0 0 0 0
        cpy     #127 + THRESHOLD
        ror			; RIGHT !LEFT 0 0 0 0 0 0

	; Read vertical paddle
        pha
        inx			; Set paddle number (1, 3)
        jsr     PREAD           ; Read paddle value
        pla
        cpy     #127 - THRESHOLD
        ror			; !UP RIGHT !LEFT 0 0 0 0 0
        cpy     #127 + THRESHOLD
        ror			; DOWN !UP RIGHT !LEFT 0 0 0 0

	; Read primary button
	tay
        lda     BUTN0-1,x	; Check button (1, 3)
        asl
        tya
        ror			; FIRE DOWN !UP RIGHT !LEFT 0 0 0

	; Read secondary button
	tay
	inx
	txa
	and	#$03		; IIgs has fourth button at TAPEIN
	tax
        lda     BUTN0-1,x	; Check button (2, 0)
        asl
        tya
	ror			; FIRE2 FIRE DOWN !UP RIGHT !LEFT 0 0

	; Finalize
        eor     #%00010100      ; FIRE2 FIRE DOWN UP RIGHT LEFT 0 0
        ldx     #$00
	bit	$C080		; Switch in LC bank 2 for R/O
        rts