routine OPEN now reacts on device number

c64/kernal/open.s

@@ -1,19 +1,62 @@
 	; Function defined on pp272-273 of C64 Programmers Reference Guide
 	;; See also http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
 
+
+open:
+
+	;; Kernal API is shared between several types of devices - we have
+	;; to dispatch the call to appropriate subroutine
+
+	lda current_device_number
+	beq open_keyboard
+	cmp #$01
+	beq open_tape
+	cmp #$02
+	beq open_rs232
+	cmp #$03
+	beq open_screen
+	cmp #$1F
+	bcs +
+	bmi open_iec
+*
+	;; Device numbers over 30 are not allowed on IEC bus
+
+	;; FALLTHROUGH to error routine
+
+open_keyboard:
+open_tape:
+open_screen:
+
+	;; XXX implement support for these devices
+	lda #$05 ; device not present
+	sta IOSTATUS
+	rts
+	
+open_rs232:
+
+	;; XXX implement support for RS-232
+	lda #$FF ; set every single error bit to discourage using RS-232
+	sta RSSTAT
+	rts
+
+open_iec:
+
+	;; XXX add FILENAM support, test it
+
 	;; Sequence is:
 	;; 1. Call current device to attention as LISTENER = $20 + device
 	;; 2. 
-open:
 
 	;; Disable IRQs, since timing matters!
-	SEI
+	sei
 
 	;; Begin sending under attention
 	jsr iec_assert_atn
 
 	;; CLK is now asserted, and we are ready to transmit a byte
-	lda #$28
+	lda #$20 ; listen
+	clc
+	adc current_device_number
 	jsr iec_tx_byte
 	bcs open_error