cc65/libsrc/vic20/joy/vic20-ptvjoy.s

;
; PTV-3 Player joystick driver for the VIC20
;
; Stefan Haubenthal, 2005-05-25
; Groepaz/Hitmen, 2002-12-23
; obviously based on Ullrichs driver :)
; Using code from Steve Schmidtke
;

        .include "zeropage.inc"

        .include "joy-kernel.inc"
        .include "joy-error.inc"
        .include "vic20.inc"

        .macpack module


; ------------------------------------------------------------------------
; Header. Includes jump table

        module_header   _vic20_ptvjoy_joy

; Driver signature

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

; Library reference

        .addr   $0000

; Jump table.

        .addr   INSTALL
        .addr   UNINSTALL
        .addr   COUNT
        .addr   READ
        .addr   0                       ; IRQ entry unused

; ------------------------------------------------------------------------
; Constants

VIA1_PRB        := VIA1         ; User port register
JOY_COUNT       = 3             ; Number of joysticks we support


.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
;       rts                     ; Run into UNINSTALL instead

; ------------------------------------------------------------------------
; 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     #<JOY_COUNT
        ldx     #>JOY_COUNT
        rts

; ------------------------------------------------------------------------
; READ: Read a particular joystick passed in A.
;

READ:   tax                     ; Joystick number into X
        bne     joy2

; Read joystick 1

joy1:   lda     #$7F            ; mask for VIA2 JOYBIT: sw3
        ldx     #$C3            ; mask for VIA1 JOYBITS: sw0,sw1,sw2,sw4
        sei                     ; necessary?

        ldy     VIA2_DDRB       ; remember the date of DDRB
        sta     VIA2_DDRB       ; set JOYBITS on this VIA for input
        lda     VIA2_JOY        ; read JOYBIT: sw3
        sty     VIA2_DDRB       ; restore the state of DDRB
        asl                     ; Shift sw3 into carry

        ldy     VIA1_DDRA       ; remember the state of DDRA
        stx     VIA1_DDRA       ; set JOYBITS on this VIA for input
        lda     VIA1_JOY        ; read JOYBITS: sw0,sw1,sw2,sw4
        sty     VIA1_DDRA       ; restore the state of DDRA

        cli                     ; necessary?
        php                     ; Save sw3 in carry
        lsr                     ; Shift sw0,sw1,sw2,sw4 into bits 1-4
        tax                     ; Save sw0,sw1,sw2
        and     #$10            ; Extract sw4 in bit 4
        sta     tmp1            ; Save sw4 in bit 4
        txa                     ; Restore sw0,sw1,sw2
        lsr                     ; Shift sw0,sw1,sw2 into bits 0-2
        and     #$07            ; Mask bits 0-2
        plp                     ; Restore sw3 in carry
        bcc     @L0             ; Is sw3 set?
        ora     #$08            ; Yes: Add sw3 in bit 3
@L0:    ora     tmp1            ; Add sw4 in bit 4
        eor     #$1F            ; Active states are inverted

        ldx     #0
        rts

; Read joystick 2

joy2:   lda     #%10000000      ; via port B Data-Direction
        sta     VIA1_DDRB       ; bit 7: out    bit 6-0: in

        dex
        bne     joy3

        lda     #$80            ; via port B read/write
        sta     VIA1_PRB        ; (output one at PB7)

        lda     VIA1_PRB        ; via port B read/write
        and     #$1F            ; get bit 4-0 (PB4-PB0)
        eor     #$1F
        rts

; Read joystick 3

joy3:   lda     #$00            ; via port B read/write
        sta     VIA1_PRB        ; (output zero at PB7)

        lda     VIA1_PRB        ; via port B read/write
        and     #$0F            ; get bit 3-0 (PB3-PB0)
        sta     tmp1            ; joy 4 directions

        lda     VIA1_PRB        ; via port B read/write
        and     #%00100000      ; get bit 5 (PB5)
        lsr
        ora     tmp1
        eor     #$1F

        ldx     #0
        rts