Added VIC20 port changes from Steve Schmidtke

git-svn-id: svn://svn.cc65.org/cc65/trunk@1376 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/vic20/readjoy.s

@@ -0,0 +1,73 @@
+;
+; Ullrich von Bassewitz, 23.09.1998
+; Adapted for Vic20 by Steve Schmidtke 05.08.2002
+;
+; unsigned readjoy (unsigned char joy);
+;
+
+     	.export		_readjoy
+
+	.include	"vic20.inc"
+
+
+.proc	_readjoy
+
+	tax			; Joystick number into X
+	bne    	joy2
+
+; Read joystick 1
+
+joy1:	lda     #$7F		
+	ldx     #$C3
+	sei			; necessary?
+	ldy	VIA1_DDRA
+	stx     VIA1_DDRA
+	ldx	VIA1_JOY
+	sty	VIA1_DDRA
+	ldy	VIA2_DDRB
+	sta     VIA2_DDRB
+	lda	VIA2_JOY	; sw3 happens to be the 7th bit (i.e negative)
+	sty	VIA2_DDRB
+	cli			; necessary?
+; all this mess below tries to normalize the returned results (see joystick.h)
+; by shifting bits around and inserting switch3 (right).
+; easier (and far smaller) would have been just to return the bits where they
+; lay and just #ifdef different joystick constants for the Vic20.
+	bmi     s3_off		; must stay valid from the VIA2_JOY load
+	txa                     ; state: sw3 on, fire ?
+	and	#$20		; find out if fire has been pressed
+	bne	f_off1
+	txa			; state: sw3 on, fire on
+	lsr
+	lsr
+	and	#$07
+	eor	#$1F		
+	rts
+f_off1:	txa                     ; state: sw3 on, fire off
+	lsr
+	lsr
+	and	#$07 
+	eor	#$0F		
+	rts
+s3_off: txa			; state: sw3 off, fire ?
+	and	#$20		; find out if fire has been pressed
+	bne	f_off2		; yeah, that's just about my sentiment by now
+	txa			; state: sw3 off, fire on
+	lsr
+	lsr
+	and	#$07
+	eor	#$17		
+	rts
+f_off2:	txa			; state: sw3 off, fire off
+	lsr
+	lsr
+	and	#$07 
+	eor	#$07		
+	rts
+ 
+; Read joystick 2 + (just return joy1)
+
+joy2:	jmp	joy1		; stub for more joysticks (pointless?) 
+
+.endproc
+