diff --git a/libsrc/atari/diopncls.s b/libsrc/atari/diopncls.s
index 50899bfe7..504994a72 100644
--- a/libsrc/atari/diopncls.s
+++ b/libsrc/atari/diopncls.s
@@ -3,44 +3,79 @@
 ;
 ; This file provides the __dio_open and __dio_close functions
 ; Since on the Atari no real open and close is necessary, they
-; do not much. The __dio_open queries the sector size of the
+; do not much. The __dio_open sets the sector size of the
 ; drive which is later used by the _dio_read and _dio_write
 ; functions.
 ;
-; unsigned char __fastcall__ _dio_open  (_driveid_t drive_id);
-; unsigned char __fastcall__ _dio_close (_driveid_t drive_id);
+; _dhandle_t    __fastcall__ _dio_open  (_driveid_t drive_id);
+; unsigned char __fastcall__ _dio_close (_dhandle_t handle);
 ;
 
  	.export		__dio_open,__dio_close
 	.export		sectsizetab
+	.import		__oserror
+	.importzp	ptr1,tmp1
 	.include	"atari.inc"
 
+
 .bss
 
 sectsizetab:
-	.res	NUMDRVS * 2
+	.res	NUMDRVS * sst_size
 
 .code
 
 
 .proc	__dio_open
 
-	asl	a	; make index from drive id
+	cmp	#NUMDRVS	; valid drive id?
+	bcs	_inv_drive
+	tay			; drive #
+	asl	a		; make index from drive id
+	asl	a
 	tax
-	lda	#128	; currently hardcoded (until I get an 815 :-)
-	sta	sectsizetab,x
+	lda	#128		; currently hardcoded (until I get an 815 :-)
+	sta	sectsizetab+sst_sectsize,x
+	sta	sectsizetab+sst_flag,x		; set flag that drive is "open"
 	lda	#0
-	sta	sectsizetab+1,x
+	sta	sectsizetab+sst_sectsize+1,x
+	sta	__oserror			; success
+	tya
+	sta	sectsizetab+sst_driveno,x
+;	lda	#SSTIDVAL
+;	sta	sectsizetab+sst_id+1,x
+	stx	tmp1
+	lda	#<sectsizetab
+	clc
+	adc	tmp1
+	sta	tmp1
+	lda	#>sectsizetab
+	adc	#0
+	tax
+	lda	tmp1
+	rts
 
-	; fall thru to __dio_close
+_inv_drive:
+	lda	#NONDEV		; non-existent device
+	sta	__oserror
+	lda	#0
+	tax
+	rts			; return NULL
 
 .endproc
 
 .proc	__dio_close
 
+	sta	ptr1
+	stx	ptr1+1
 	lda	#0
+	ldy	#sst_flag
+	sta	(ptr1),y
+;	ldy	#sst_id
+;	sta	(ptr1),y
+	sta	__oserror	; success
 	tax
-	rts		; return no error
+	rts			; return no error
 
 .endproc