cpu: saml21: add periph/pm support

cpu/saml21/Makefile.features

@@ -0,0 +1 @@
+FEATURES_PROVIDED += periph_pm

cpu/saml21/Makefile.include

@@ -1,5 +1,7 @@
 export CPU_ARCH = cortex-m0plus
 export CPU_FAM  = saml21
 
+USEMODULE += pm_layered
+
 include $(RIOTCPU)/sam0_common/Makefile.include
 include $(RIOTCPU)/Makefile.include.cortexm_common

cpu/saml21/include/periph_cpu.h

@@ -60,6 +60,8 @@ typedef enum {
 /** @} */
 #endif /* ndef DOXYGEN */
 
+#define PM_NUM_MODES    (3)
+
 #ifdef __cplusplus
 }
 #endif

cpu/saml21/periph/pm.c

@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2017 Kaspar Schleiser <kaspar@schleiser.de>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     cpu_saml21
+ * @{
+ *
+ * @file
+ * @brief       Implementation of the kernels power management interface
+ *
+ * @author      Kaspar Schleiser <kaspar@schleiser.de>
+ *
+ * @}
+ */
+
+#include "periph/pm.h"
+
+#define ENABLE_DEBUG (0)
+#include "debug.h"
+
+void pm_set(unsigned mode)
+{
+    if (mode < PM_NUM_MODES) {
+        uint32_t _mode;
+
+        switch (mode) {
+            case 0:
+                DEBUG("pm_set(): setting BACKUP mode.\n");
+                _mode = PM_SLEEPCFG_SLEEPMODE_BACKUP;
+                break;
+            case 1:
+                DEBUG("pm_set(): setting STANDBY mode.\n");
+                _mode = PM_SLEEPCFG_SLEEPMODE_STANDBY;
+                break;
+            case 2:
+                DEBUG("pm_set(): setting IDLE mode.\n");
+                _mode = PM_SLEEPCFG_SLEEPMODE_IDLE2;
+                break;
+        }
+
+        /* write sleep configuration */
+        PM->SLEEPCFG.bit.SLEEPMODE = _mode;
+        /* make sure value has been set */
+        while (PM->SLEEPCFG.bit.SLEEPMODE != _mode) {}
+    }
+
+    /* Executes a device DSB (Data Synchronization Barrier) */
+    __DSB();
+    /* Enter standby mode */
+    __WFI();
+}