diff --git a/cpu/cortexm_common/cortexm_init.c b/cpu/cortexm_common/cortexm_init.c
index 5419d92db..39ff3a908 100644
--- a/cpu/cortexm_common/cortexm_init.c
+++ b/cpu/cortexm_common/cortexm_init.c
@@ -49,4 +49,7 @@ void cortexm_init(void)
     for (IRQn_Type i = 0; i < (int) CPU_IRQ_NUMOF; i++) {
         NVIC_SetPriority(i, CPU_DEFAULT_IRQ_PRIO);
     }
+
+    /* enable wake up on events for __WFE CPU sleep */
+    SCB->SCR |= SCB_SCR_SEVONPEND_Msk;
 }
diff --git a/cpu/cortexm_common/include/cpu.h b/cpu/cortexm_common/include/cpu.h
index c2a79cbac..fbffb0f2d 100644
--- a/cpu/cortexm_common/include/cpu.h
+++ b/cpu/cortexm_common/include/cpu.h
@@ -102,6 +102,18 @@ static inline void cpu_print_last_instruction(void)
     printf("%p\n", (void*) lr_ptr);
 }
 
+/**
+ * @brief   Put the CPU into the 'wait for event' sleep mode
+ *
+ * This function is meant to be used for short periods of time, where it is not
+ * feasible to switch to the idle thread and back.
+ */
+static inline void cpu_sleep_until_event(void)
+{
+    __SEV();
+    __WFE();
+}
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/cpu/nrf51/periph/hwrng.c b/cpu/nrf51/periph/hwrng.c
deleted file mode 100644
index fa234290c..000000000
--- a/cpu/nrf51/periph/hwrng.c
+++ /dev/null
@@ -1,65 +0,0 @@
-/*
- * Copyright (C) 2014-2016 Freie Universität Berlin
- *
- * 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_nrf51
- * @{
- *
- * @file
- * @brief       Driver for the NRF51822 random number generator
- *
- * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
- * @author      Frank Holtz <frank-riot2015@holtznet.de>
- *
- * @}
- */
-
-#include "cpu.h"
-#include "periph/hwrng.h"
-
-void hwrng_init(void)
-{
-    /* The RNG is initiated every time when RNG read is called
-     * This reduces power consumption when RNG is not needed
-     */
-}
-
-void hwrng_read(uint8_t *buf, unsigned int num)
-{
-    unsigned int count = 0;
-
-    /* power on RNG */
-    NRF_RNG->POWER = 1;
-    /* Generate events when RNG is finished */
-    NRF_RNG->INTENSET = RNG_INTENSET_VALRDY_Msk;
-    /* Start Task */
-    NRF_RNG->TASKS_START = 1;
-    /* NRF51 PAN #21 */
-    NRF_RNG->EVENTS_VALRDY = 0;
-
-    while (count < num) {
-        /* sleep until number is generated */
-        while (NRF_RNG->EVENTS_VALRDY == 0) {
-            /* enable wake up on events for __WFE CPU sleep */
-            SCB->SCR |= SCB_SCR_SEVONPEND_Msk;
-            /* sleep until next event */
-            __SEV();
-            __WFE();
-            __WFE();
-        }
-
-        buf[count++] = (uint8_t)NRF_RNG->VALUE;
-        /* NRF51 PAN #21 */
-        NRF_RNG->EVENTS_VALRDY = 0;
-        /* clear interrupt state */
-        NVIC_ClearPendingIRQ(RNG_IRQn);
-    }
-
-    /* power off RNG */
-    NRF_RNG->POWER = 0;
-}
diff --git a/cpu/nrf52/periph/hwrng.c b/cpu/nrf5x_common/periph/hwrng.c
similarity index 56%
rename from cpu/nrf52/periph/hwrng.c
rename to cpu/nrf5x_common/periph/hwrng.c
index c7ec673ce..832d1378b 100644
--- a/cpu/nrf52/periph/hwrng.c
+++ b/cpu/nrf5x_common/periph/hwrng.c
@@ -1,6 +1,6 @@
 /*
- * Copyright (C) 2015 Jan Wagner <mail@jwagner.eu>
- *               2016 Freie Universität Berlin
+ * Copyright (C) 2014-2016 Freie Universität Berlin
+ *               2015 Jan Wagner <mail@jwagner.eu>
  *
  * 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
@@ -8,13 +8,14 @@
  */
 
 /**
- * @ingroup     cpu_nrf52
+ * @ingroup     cpu_nrf5x_common
  * @{
  *
  * @file
  * @brief       Implementation of the hardware random number generator interface
  *
  * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
+ * @author      Frank Holtz <frank-riot2015@holtznet.de>
  * @author      Jan Wagner <mail@jwagner.eu>
  *
  * @}
@@ -32,14 +33,27 @@ void hwrng_read(uint8_t *buf, unsigned int num)
 {
     unsigned int count = 0;
 
+    /* power on RNG */
+#ifdef CPU_FAM_NRF51
+    NRF_RNG->POWER = 1;
+#endif
     NRF_RNG->TASKS_START = 1;
 
+    /* read the actual random data */
     while (count < num) {
-        while (NRF_RNG->EVENTS_VALRDY == 0);
+        /* sleep until number is generated */
+        while (NRF_RNG->EVENTS_VALRDY == 0) {
+            cpu_sleep_until_event();
+        }
 
-        NRF_RNG->EVENTS_VALRDY = 0;
         buf[count++] = (uint8_t)NRF_RNG->VALUE;
+        /* NRF51 PAN #21 -> read value before clearing VALRDY */
+        NRF_RNG->EVENTS_VALRDY = 0;
     }
 
+    /* power off RNG */
     NRF_RNG->TASKS_STOP = 1;
+#ifdef CPU_FAM_NRF51
+    NRF_RNG->POWER = 0;
+#endif
 }