diff --git a/regnual/sys.c b/regnual/sys.c
index fc8d0a9..702e4c8 100644
--- a/regnual/sys.c
+++ b/regnual/sys.c
@@ -15,28 +15,21 @@ void entry (void)
 {
   asm volatile ("ldr	r0, =__ram_end__\n\t"
 		"ldr	r1, =__main_stack_size__\n\t"
-		"subs	r0, r0, r1\n\t"
-		"msr	PSP, r0\n\t" /* Process (main routine) stack */
-		"movs	r0, #0\n\t"
+		"sub	r0, r0, r1\n\t"
+		"mov	sp, r0\n\t"
+		"mov	r0, #0\n\t"
 		"ldr	r1, =_bss_start\n\t"
-		"ldr	r2, =_bss_start\n"
+		"ldr	r2, =_bss_end\n"
 	"0:\n\t"
-		"cmp	r1, r2\n\t"
-		"bge	1f\n\t"
-		"str	r0, [r1]\n\t"
-		"adds	r1, r1, #4\n\t"
-		"b	0b\n"
-	"1:\n\t"
-		"movs	r0, #2\n\t" /* Switch to PSP */
-		"msr	CONTROL, r0\n\t"
-		"isb\n\t"
-		"movs	r0, #0\n\t"
-		"msr	BASEPRI, r0\n\t" /* Enable interrupts */
-		"cpsie	i\n\t"
+		"str	r0, [r1], #4\n\t"
+		"cmp	r2, r1\n\t"
+		"bhi	0b\n\t"
+		"cpsie	i\n\t"	/* Enable interrupts */
+		"mov	r0, #0\n\t"
 		"mov	r1, r0\n\t"
 		"bl	main\n"
-	"2:\n\t"
-		"b	2b\n"
+	"1:\n\t"
+		"b	1b\n"
 		: /* no output */ : /* no input */ : "memory");
 }