diff --git a/BaS_gcc/sources/xhdi_sd.c b/BaS_gcc/sources/xhdi_sd.c
index 5b411f1..f69583c 100644
--- a/BaS_gcc/sources/xhdi_sd.c
+++ b/BaS_gcc/sources/xhdi_sd.c
@@ -32,30 +32,6 @@
 
 static BPB sd_bpb[4];	/* space for four partitions on SD card */
 
-static xhdi_call_fun old_vector = NULL;
-extern uint32_t xhdi_vec(uint16_t *stack);
-
-__attribute__((__interrupt__)) xhdi_call_fun xhdi_sd_install(xhdi_call_fun ov)
-{
-	old_vector = ov;
-	uint32_t *_drvbits = (uint32_t *) 0x4c2;
-
-	__asm__ __volatile__ (
-			"move.l		%[xhdi_call],d1\n\t"
-			"move.l		d1,(sp)\n\t"	/* FIXME: dirty overwrite of saved register on stack with return value */
-			"move.l		d1,8(sp)\n\t"
-			: /* output */
-			: [xhdi_call]"g"(xhdi_vec)
-			: "d1","memory");
-
-	*_drvbits |= (uint32_t) 1 << ('S' - 'A');
-	/*
-	 * this is just to make the compiler happy, the return value is overwritten anyway. Therefore we previously overwrite
-	 * the saved register value on the stack so everything is as we want it to be
-	 */
-	return (xhdi_call_fun) xhdi_call;
-}
-
 uint16_t xhdi_version(void)
 {
 	xprintf("xhdi_version() called\r\n");
diff --git a/BaS_gcc/sources/xhdi_vec.S b/BaS_gcc/sources/xhdi_vec.S
index 9dd2f7f..7b1c7d3 100644
--- a/BaS_gcc/sources/xhdi_vec.S
+++ b/BaS_gcc/sources/xhdi_vec.S
@@ -3,13 +3,36 @@
 //
 		.extern	_xhdi_call
 		.globl	_xhdi_vec
+		.globl	_xhdi_sd_install
 
+//
+// this is where the XHDI cookie points to:
+//
+
+		.text
 _xhdi_vec:
-		lea     -12(sp),sp
+		lea     -12(sp),sp		// save all used registers according to XHDI spec
 		movem.l d1/a0-a1,(sp)
-		pea     16(sp)
-		jsr		_xhdi_call
-		addq.l  #4,sp
-		movem.l (sp),d1/a0-a1
+		pea     16(sp)			// forward address of parameters on stack
+		jsr		_xhdi_call		// to internal routine
+		addq.l  #4,sp			// correct stack
+		movem.l (sp),d1/a0-a1	// restore registers
 		lea     12(sp),sp
 		rts
+
+		.equ	_drvbits, 0x4c2
+
+		.data
+_old_vector:
+		.ds.l	1
+
+		.text
+
+//
+// trap #0 handler to bring the address of the disk routines into TOS
+//
+_xhdi_sd_install:
+		move.l	4(sp),d0		// address of the old XHDI vector
+		move.l	d0,_old_vector	// save it in case we need it
+		move.l	_xhdi_vec,d0	// return our BaS vector to TOS
+		rte