Fix user context save

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@1203 42af7a65-404d-4744-a932-0658087f49c3

1 files changed, 16 insertions, 13 deletions

diff --git a/nuttx/arch/sh/src/sh1/sh1_saveusercontext.S b/nuttx/arch/sh/src/sh1/sh1_saveusercontext.S
index d9a430816..ee6952f46 100644
--- a/nuttx/arch/sh/src/sh1/sh1_saveusercontext.S
+++ b/nuttx/arch/sh/src/sh1/sh1_saveusercontext.S
@@ -80,29 +80,32 @@ _up_saveusercontext:
 	/* On entry, R4 contains a reference to the register save structure
 	 * to populate.
 	 *
-	 * Save a nonzero value for R0 in the register save area.  This will
-	 * will be the apparent return value when a context switch back to
-	 * this thread is performed.
+	 * Re-position to the end of the structure (+4_ so that we can use
+	 * auto decrement 
 	 */
 
-	mov	#1, r0
-	mov.l	r0, @r4
-
-	/* Move to the end of the structure so that we can use auto decrement */
-
-	add	#(XCPTCONTEXT_SIZE-4), r0
+	add	#(XCPTCONTEXT_SIZE), r4	/* R4: Address of last entry + 4 */
 
 	/* Save the necessary registers */
 
 	stc     sr, r0			/* Get and save the SR */
 	mov.l	r0, @-r4
 	sts.l	pr, @-r4		/* The return address is the restore PC */
-	add	#-(10*4), r4		/* Skip over r0-r7, mach and macl */
-	mov.l	r15, @-r4
-	stc.l	gbr, @-r4
+	add	#-(7*4), r4		/* Skip over r4, r7-r1.  R4 points at R1 storage */
+
+	/* Save a nonzero value for R0 in the register save area.  This will
+	 * will be the apparent return value when a context switch back to
+	 * this thread is performed.
+	 */
+
+	mov	#1, r0			/* Save R0=1 (return value) */
+	mov.l	r0, @-r4
+	add	#-(2*4), r4		/* Skip over mach and macl.  R4 points at R15 storage. */
+	mov.l	r15, @-r4		/* SP */
+	stc.l	gbr, @-r4		/* GBR & PR */
 	sts.l	pr, @-r4
 
-	mov.l	r14, @-r4
+	mov.l	r14, @-r4		/* R14-R8 */
 	mov.l	r13, @-r4
 	mov.l	r12, @-r4
 	mov.l	r11, @-r4