work towards CHKIN, CHKOUT and CLRCHN

c64/kernal/open.s

@@ -8,13 +8,23 @@
 ;; CPU registers that has to be preserved (see [RG64]): none
 ;;
 
-;; XXX this is only a test implementation, does not do what the Kernal does!
 
 open:
 
-	;; LAT / FAT / SAT support implemented according to
-	;; 'Compute's Mapping the Commodore 64', page 52
+	;; Reset status
+	jsr kernalstatus_reset
 
+	;; Check if the logical file number is unique
+	ldy LDTND
+*
+	beq +
+	dey
+	lda LAT, y
+	cmp current_logical_filenum
+	beq kernalerror_FILE_ALREADY_OPEN
+	cpy #$00
+	jmp -
+*
 	;; Check if we have space in tables
 
 	ldy LDTND
@@ -22,15 +32,16 @@ open:
 	bcs +
 	bmi open_has_space
 *
-	;; Table is full - according to https://codebase64.org/doku.php?id=base:kernalreference
-	;; C flag set means error occured
-	sec
-	rts
+	;; Table is full
+	jmp kernalerror_TOO_MANY_OPEN_FILES
 
 open_has_space:
 
 	;; Update the tables
 
+	;; LAT / FAT / SAT support implemented according to
+	;; 'Compute's Mapping the Commodore 64', page 52
+
 	lda current_logical_filenum
 	sta LAT, y
 	lda current_device_number
@@ -40,66 +51,7 @@ open_has_space:
 
 	iny
 	sty LDTND
-
-	;; 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:
-
-	;; Part implemented according to https://www.pagetable.com/?p=1031, https://github.com/mist64/cbmbus_doc
-	;; XXX note: this is only a temporary test implementation, real 'open' does not send anything to IEC,
-	;; see http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
-
-	;; Request device to talk
-	lda current_device_number
-	jsr talk
-	bcs open_iec_error
-
-	;; Send secondary address
-	lda current_secondary_address
-	jsr second
-	bcs open_iec_error
-
-	;; Turnaround
-	jsr iec_turnaround_to_listen
-	bcs open_iec_error
-
-	;; Indicate success
-	lda #$00
 	clc
-
-open_iec_error:
-	;; Carry flag will be set by low-level routines
 	rts
+