put IOINIT at $FDA3. Issue #20

c64/kernal/fda3.ioinit.s

@@ -0,0 +1,40 @@
+; Function defined on pp272-273 of C64 Programmers Reference Guide
+ioinit:
+
+	; Set $00/$01 port mode and value
+	; We want BASIC and KERNAL ROMs mapped, and datasette motor off
+	; (https://www.c64-wiki.com/wiki/Zeropage)
+	LDA #$2F
+	STA $00
+	LDA #$27
+	STA $01
+
+	;; Enable CIA1 IRQ and ~50Hz timer
+	;; (https://csdb.dk/forums/?roomid=11&topicid=69037)
+	lda #$7f
+	sta $DC0D 		; First disable all
+
+	;; Set timer interval to ~1/60th of a second
+	;; (This value was calculated by running a custom IRQ haandler on a C64
+	;; with original KERNAL, and writing the values of $DC04/5 to the screen
+	;; in the IRQ handler to see roughly what value the timers must be set to)
+	lda #<16380
+	sta $dc04
+	lda #>16380
+	sta $dc05
+
+	;; Enable timer interrupt
+	lda #$81
+	sta $dc0d
+
+	;; Enable timer A to run continuously
+	;; (http://codebase64.org/doku.php?id=base:timerinterrupts)
+	lda #$11
+	sta $dc0e
+	lda $dc0d
+
+	;; Set DDR on CIA2 for IEC bus, VIC-II banking
+	lda #$3b
+	sta $dd02
+	
+	rts