cpu/samd5x: allow to block IDLE mode

Make it possible to prevent the CPU clock from stopping.

cpu/samd5x/include/periph_cpu.h

@@ -53,7 +53,11 @@ extern "C" {
  * @name    Power mode configuration
  * @{
  */
-#define PM_NUM_MODES        (3)
+#define PM_NUM_MODES       4            /**< Backup, Hibernate, Standby, Idle */
+
+#ifndef PM_BLOCKER_INITIAL
+#define PM_BLOCKER_INITIAL 0x00010101   /**< Block all modes but Idle */
+#endif
 /** @} */
 
 /**

cpu/samd5x/periph/pm.c

@@ -45,11 +45,13 @@ void pm_set(unsigned mode)
             _mode = PM_SLEEPCFG_SLEEPMODE_STANDBY;
             deep = 1;
             break;
-        default: /* Falls through */
         case 3:
             DEBUG_PUTS("pm_set(): setting IDLE2 mode.");
             _mode = PM_SLEEPCFG_SLEEPMODE_IDLE2;
             break;
+        default:
+            /* no sleep */
+            return;
     }
 
     /* write sleep configuration */