From b6140f15f3f761db057a90e3d5966f97338776e6 Mon Sep 17 00:00:00 2001
From: DipSwitch <dipswitch@ownage4u.nl>
Date: Thu, 7 Apr 2016 00:27:26 +0200
Subject: [PATCH] cpu/cortex-m: Enable STKALIGN to make the Cortex-M keep the
 stack 8 byte aligned on 4 byte aligned stack pointers

---
 cpu/cortexm_common/cortexm_init.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/cpu/cortexm_common/cortexm_init.c b/cpu/cortexm_common/cortexm_init.c
index 6e098b65cb..1875da98fd 100644
--- a/cpu/cortexm_common/cortexm_init.c
+++ b/cpu/cortexm_common/cortexm_init.c
@@ -52,4 +52,12 @@ void cortexm_init(void)
 
     /* enable wake up on events for __WFE CPU sleep */
     SCB->SCR |= SCB_SCR_SEVONPEND_Msk;
+
+    /* for Cortex-M3 r1p0 and up the STKALIGN option was added, but not automatically
+     * enabled until revision r2p0. For 64bit function arguments to work properly this
+     * needs to be enabled.
+     */
+#ifdef SCB_CCR_STKALIGN_Msk
+    SCB->CCR |= SCB_CCR_STKALIGN_Msk;
+#endif
 }