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cc65/libsrc/vic20/joy/vic20-stdjoy.s
2023-02-26 20:03:41 +01:00

120 lines
3.6 KiB
ArmAsm

;
; Standard joystick driver for the VIC20. May be used multiple times when linked
; to the statically application.
;
; Ullrich von Bassewitz, 2002-12-20
; Using code from Steve Schmidtke
;
.include "zeropage.inc"
.include "joy-kernel.inc"
.include "joy-error.inc"
.include "vic20.inc"
.macpack generic
.macpack module
; ------------------------------------------------------------------------
; Header. Includes jump table
module_header _vic20_stdjoy_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
; ------------------------------------------------------------------------
; Constants
JOY_COUNT = 1 ; Number of joysticks we support
; ------------------------------------------------------------------------
; Data.
.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
.assert JOY_ERR_OK = 0, error
tax
; 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.
; The current implemenation will ignore the joystick number because we do only
; have one joystick
READ: 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_PB ; 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_PA1 ; 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