--- cci/d/event/prvinstr.s	2019/07/28 12:24:19	1.1.1.1
+++ cci/d/event/prvinstr.s	2019/07/28 12:30:55	1.1.1.2
@@ -117,13 +117,15 @@ _prvinstr:
 	movab	(sp),_savvec0		/* Save current SP */
 	movpsl	_savvec1		/* Save current PSL */	
 	movl	fp,_savvec2		/* Save current FP */
+	mfpr	$KSP,_savvec9		/* Save kernal stack pointer */
+	mfpr	$USP,_savveca		/* Save user stack pointer */
 
 	mtpr	$0,$ISP			/* Init ISP to 0  */
 	movab	_pcb0,r1		/* Init PCB0	*/
 	mtpr	r1,$PCBB		/* Set PCBB to pcb0 */
 
-	movl	_savvec0,PCB_KSP(r1)	/* PCB_KSP = current SP */
-	movl	$-1,PCB_USP(r1)		/* PCB_USP = -1 */
+	movl	_savvec9,PCB_KSP(r1)	/* PCB_KSP = saved value of KSP */
+	movl	_savveca,PCB_USP(r1)		/* PCB_USP = -1 */
 	movl	$0,PCB_R0(r1)
 	movl	$0x11111111,PCB_R1(r1)
 	movl	$0x22222222,PCB_R2(r1)
@@ -338,7 +340,9 @@ rtnld:
 #/*	the stack. So svpctx can use it		*/
 
 9:
-nxts:	mtpr	_savvec0,$ISP	/* Init ISP = original SP */
+nxts:	mtpr	_savvec0,$ISP	/* Init ISP = original ISP */
+	mtpr	_savvec9,$KSP	/* Init KSP = original KSP */
+	mtpr	_savveca,$USP	/* Init USP = original USP */
 	movab	_pcb1,r6
 	movl	r6,r7		/* r7 = address  of Pcb1 */
 	mtpr	r7,$PCBB	/* Set PCBB = physical address PCB1 */
@@ -461,7 +465,7 @@ nxts:	mtpr	_savvec0,$ISP	/* Init ISP = o
 	mtpr	$0,$ISP			/* Init ISP to 0  */
 	movab	_pcb0,r1		/* Init PCB0	*/
 	mtpr	r1,$PCBB		/* Set PCBB to pcb0 */
-	movl	_savvec0,PCB_KSP(r1)	/* PCB_KSP = current SP */
+	movl	_savvec9,PCB_KSP(r1)	/* PCB_KSP = saved value of KSP */
 	movl	$-1,PCB_USP(r1)		/* PCB_USP = -1 */
 	movl	$0x5e5e5e5e,PCB_ACCM(r1) /* set MS of fpp's acc. */
 	movl	$0x6f6f6f6f,PCB_ACCL(r1) /* set LS of fpp's acc. */
@@ -560,8 +564,6 @@ nxts:	mtpr	_savvec0,$ISP	/* Init ISP = o
 	movab	_pcb0,r1	/* Set PCBB to pcb0			*/
 	mtpr	r1,$PCBB
 
-	movl	$0,_pcb0+PCB_KSP	/* PCB_KSP = PCB_USP = 0 */
-	movl	$0,_pcb0+PCB_USP
 	movl	$0x041d0000,-(sp) 	/* Set PSL,PC  on stack for next REI */
 					/* REI to K mode and IPL == 0x1d  */
 	movab	rei1,r3
@@ -594,8 +596,8 @@ rei1:
 #
 #	REI K mode to K mode; is =0; ipl = 1d
 1:
-	subl3	$16,r2,_pcb0	/* set PCB_KSP to SP-16		*/
-	subl3	$24,r2,_pcb0+PCB_USP	/* Set PCB_USP to SP-24	*/
+	mtpr	_savvec9,$KSP	/* restore kernal stack pointer */
+	mtpr	_savveca,$USP	/* restore user stack pointer */
 	mtpr	$0,$ISP
 	pushl	$0x001d0000	/* Set up PSL,PC on stack for REI */
 	pushab	1f		/* PSL_IS = 0; PSL_IPL = 1d; K mode */
@@ -633,14 +635,14 @@ rei2:
 #	** SISR = bit 7 & 2 ON				
 #
 1:
-	movl	$0x140004,*$HSR  /* Set HISR : pending console transmit */
-				 /* interrupt at IPL#0x14  */
-	movl	$0x82,*$SSR	/* Set SISR : pending IPL#7, IPL#2 */
 
 	movl	_scb+44,_savvec4   /* Save int vector for console trans int. */
 	movl	_scb+SIVEC1-24,_savvec6 /* Save int vector for IPL# 7    */
 	movab	hs14,_scb+44		/* New vector for HISR #0x14 */
 	movab	ss7,_scb+SIVEC1-24	/* New vector soft int. #7 */
+	movl	$0x140004,*$HSR  /* Set HISR : pending console transmit */
+				 /* interrupt at IPL#0x14  */
+	movl	$0x82,*$SSR	/* Set SISR : pending IPL#7, IPL#2 */
 	brw	1f
 #
 #	**************
@@ -678,6 +680,7 @@ rei3:
 	pushl	$0x00130000		/* Set up PSL,PC for REI	*/
 	pushab	9f
 	movab	rei4,r3
+	mfpr	$ISP,r4		/* save interrupt stack pointer	*/
 rei4:
 	rei			/* Should take pending hardware int. #0x14 */
 	movl	$14,r0		/* error : REI fell thru */
@@ -712,7 +715,7 @@ hsr_hdl:			/* This is where REI should c
 #
 1:
 	movab	(sp),r1		/* check if current SP = (ISP-8)	*/
-	mfpr	$ISP,r2
+	movl	r4,r2		/* r4 is saved ISP	*/
 	subl2	$8,r2
 	cmpl	r1,r2
 	beql	1f
@@ -776,6 +779,7 @@ sw7:				/* This is where REI comes	*/
 	movl	_savvec6,_scb+SIVEC1-24	/*restore original vector for	*/
 					/*ipl #7			*/
 	movl	_savvec0,sp
+	mtpr	_savveca,$USP	/* Restore user stack pointer */
 	pushl	$0x1000000	/* Set up to REI to user, IPL = 0, IS = 0 */
 	pushab	1f
 	mtpr	$0,$ISP		/* Set ISP to 0			*/
@@ -814,7 +818,7 @@ rei6:
 #	still running in user mode	
 #
 1:
-	movl	_savvec0,sp
+	movl	_savveca,sp	/* restore stack pointer (user stack) */
 	pushl	$0x1000000	/* Set up to REI to another user */
 	pushab	1f
 	movab	rei7,r3
@@ -836,13 +840,14 @@ rei7:
 	beql	1f
 	movl	$33,r0
 	jmp    *badrtn		/*sp not set to USP when mode = U*/
-1:
-	movl	$2,*$SSR	/* This is cheating : Set SISR	*/
-	movl	_scb+SIVEC1,r4	/* directly in PSA */
+1:			
+	movl	_scb+SIVEC1,r4
 	movab	sw2,_scb+SIVEC1 /* New handler for software int.#2 */
 	pushl	$0x01000000	/* Set PSL,PC to REI to user ipl0 */
 	pushab	1f
 	movab	rei8,r3
+	movl	$2,*$SSR	/* This is cheating : Set SISR	*/
+				/* directly in PSA */
 rei8:
 	rei		/* Use REI with pending int #2 in SISR to get back */
 	movl	$14,r0
@@ -854,12 +859,14 @@ rei8:
 #
 	.align	2
 sw2:	
-	movl	r4,_scb+SIVEC1
 	mtpr	$31,$IPL
+	movl	r4,_scb+SIVEC1	/* restore software vector for int#2 */
 	movl	(sp)+,r0
 	movl	(sp)+,r0
 	movl	_savvec0,sp	/* Original SP		*/
 	movl	_savvec2,fp
+	mtpr	_savvec9,$KSP	/* Restore kernal stack pointer */
+	mtpr	_savveca,$USP	/* Restore user stack pointer */
 	ret
 #
 #