diff --git a/cpu/arm/aducrf101/Makefile.aducrf101 b/cpu/arm/aducrf101/Makefile.aducrf101
index a613fd28f..337da3385 100644
--- a/cpu/arm/aducrf101/Makefile.aducrf101
+++ b/cpu/arm/aducrf101/Makefile.aducrf101
@@ -101,6 +101,7 @@ CONTIKI_CPU_DIRS += ../common/CMSIS
 
 CONTIKI_CPU_DIRS += .
 CONTIKI_SOURCEFILES += slip-arch.c
+CONTIKI_SOURCEFILES += rtimer-arch.c
 
 CONTIKI_CPU_DIRS += dev
 CONTIKI_SOURCEFILES += uart.c
diff --git a/cpu/arm/aducrf101/aducrf101-contiki.h b/cpu/arm/aducrf101/aducrf101-contiki.h
index f82231cba..00fd8765d 100644
--- a/cpu/arm/aducrf101/aducrf101-contiki.h
+++ b/cpu/arm/aducrf101/aducrf101-contiki.h
@@ -45,8 +45,8 @@
 typedef uint32_t clock_time_t;
 typedef uint16_t uip_stats_t;
 
-typedef unsigned long rtimer_clock_t;
-#define RTIMER_CLOCK_LT(a, b)     ((signed long)((a) - (b)) < 0)
+typedef uint32_t rtimer_clock_t;
+#define RTIMER_CLOCK_LT(a, b)  ((int32_t)((a) - (b)) < 0)
 rtimer_clock_t rtimer_arch_now(void);
 
 #endif
diff --git a/cpu/arm/aducrf101/rtimer-arch.c b/cpu/arm/aducrf101/rtimer-arch.c
index 14518eb84..4f6b3caa3 100644
--- a/cpu/arm/aducrf101/rtimer-arch.c
+++ b/cpu/arm/aducrf101/rtimer-arch.c
@@ -35,25 +35,104 @@
  * \author Jim Paris <jim.paris@rigado.com>
  */
 
+#include <contiki.h>
 #include "rtimer-arch.h"
+#include "aducrf101-contiki.h"
 
+/* rtimer on the ADuCRF101 is implemented with the "wakeup" timer.
+   (timer 2).  It should be clocked from an external crystal,
+   but if that doesn't seem to be present, this code will select the
+   imprecise internal 32.768 KHz oscillator instead. */
+
+static void
+_timer2_enable(int enable)
+{
+  T2CON_ENABLE_BBA = enable;
+  clock_time_t now = clock_time();
+  while(T2STA_CON_BBA) {
+    /* Synchronizing settings may fail if the chosen clock isn't running;
+       wait no more than 1ms for it */
+    if((clock_time() - now) > (CLOCK_SECOND / 1000)) {
+      break;
+    }
+  }
+}
+static uint32_t
+_timer2_val(void)
+{
+  /* This is atomic because the FREEZE bit is set in T2CON. */
+  uint32_t now;
+  now = pADI_WUT->T2VAL0;
+  now |= pADI_WUT->T2VAL1 << 16;
+  return now;
+}
+static uint32_t
+_timer2_measure_freq(void)
+{
+  const int test_usec = 10000;
+  uint32_t now = _timer2_val();
+  clock_delay_usec(test_usec);
+  return (_timer2_val() - now) * (1000000 / test_usec);
+}
 void
 rtimer_arch_init(void)
 {
+  uint32_t freq;
+  const char *timer = "LFXTAL";
+
+  _timer2_enable(0);
+  pADI_WUT->T2CON = T2CON_PRE_DIV1 | T2CON_MOD_FREERUN | T2CON_FREEZE_EN |
+    T2CON_WUEN_EN;
+
+  /* Try 32.768 KHz crystal */
+  pADI_WUT->T2CON |= T2CON_CLK_LFXTAL;
+  _timer2_enable(1);
+  freq = _timer2_measure_freq();
+
+  if(freq < 20000 || freq > 40000) {
+    /* No good; use 32.768 KHz internal oscillator */
+    _timer2_enable(0);
+    pADI_WUT->T2CON &= ~T2CON_CLK_MSK;
+    pADI_WUT->T2CON |= T2CON_CLK_LFOSC;
+    _timer2_enable(1);
+    freq = _timer2_measure_freq();
+    timer = "LFOSC";
+  }
+
+  printf("Using %s for rtimer (%ld Hz)\n", timer, freq);
+
+  /* Enable interrupt in NVIC, but disable in WUT for now. */
+  pADI_WUT->T2IEN = 0;
+  NVIC_EnableIRQ(WUT_IRQn);
 }
-/*---------------------------------------------------------------------------*/
-void
-rtimer_arch_schedule(rtimer_clock_t t)
-{
-}
-/*---------------------------------------------------------------------------*/
-void
-rtimer_arch_set(rtimer_clock_t t)
-{
-}
-/*---------------------------------------------------------------------------*/
 rtimer_clock_t
 rtimer_arch_now(void)
 {
-  return 0;
+  /* This is atomic because the FREEZE bit is set in T2CON. */
+  return _timer2_val();
+}
+void
+rtimer_arch_schedule(rtimer_clock_t t)
+{
+  uint32_t now = _timer2_val();
+
+  /* Minimum of 5 wakeup timer ticks */
+  if((int32_t)(t - now) < 5) {
+    t = now + 5;
+  }
+
+  /* Set T2WUFB to match at target time */
+  T2IEN_WUFB_BBA = 0;
+  pADI_WUT->T2WUFB0 = (t & 0xffff);
+  pADI_WUT->T2WUFB1 = (t >> 16);
+  T2IEN_WUFB_BBA = 1;
+}
+void
+WakeUp_Int_Handler(void)
+{
+  /* clear interrupt */
+  T2CLRI_WUFB_BBA = 1;
+  /* disable T2WUFB match */
+  T2IEN_WUFB_BBA = 0;
+  rtimer_run_next();
 }
diff --git a/cpu/arm/aducrf101/rtimer-arch.h b/cpu/arm/aducrf101/rtimer-arch.h
index 88399bd87..ec28dcf7d 100644
--- a/cpu/arm/aducrf101/rtimer-arch.h
+++ b/cpu/arm/aducrf101/rtimer-arch.h
@@ -40,7 +40,7 @@
 
 #include <stdint.h>
 
-#define RTIMER_ARCH_SECOND (1000)
+#define RTIMER_ARCH_SECOND (32768)
 
 #include "sys/rtimer.h"
 
diff --git a/platform/ev-aducrf101mkxz/contiki-main.c b/platform/ev-aducrf101mkxz/contiki-main.c
index 944e2d278..0dd4dee18 100644
--- a/platform/ev-aducrf101mkxz/contiki-main.c
+++ b/platform/ev-aducrf101mkxz/contiki-main.c
@@ -132,6 +132,7 @@ main(int argc, char **argv)
   process_init();
   process_start(&etimer_process, NULL);
   ctimer_init();
+  rtimer_init();
 
   set_rime_addr();