Disable us ticker in deep-sleep mode.

targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF51/sleep.c

@@ -18,6 +18,8 @@
 #include "mbed_interface.h"
 #include "softdevice_handler.h"
 #include "nrf_soc.h"
+#include "nrf_timer.h"
+#include "us_ticker.h"
 
 // Mask of reserved bits of the register ICSR in the System Control Block peripheral
 // In this case, bits which are equal to 0 are the bits reserved in this register
@@ -25,6 +27,8 @@
 
 #define FPU_EXCEPTION_MASK 0x0000009F
 
+extern bool us_ticker_initialized;
+
 void hal_sleep(void)
 {
     // ensure debug is disconnected if semihost is enabled....
@@ -75,6 +79,15 @@ void hal_sleep(void)
 
 void hal_deepsleep(void)
 {
+    if (us_ticker_initialized) {
+        nrf_timer_task_trigger(NRF_TIMER1, NRF_TIMER_TASK_STOP);
+    }
+
     hal_sleep();
+
+    if (us_ticker_initialized) {
+        nrf_timer_task_trigger(NRF_TIMER1, NRF_TIMER_TASK_START);
+    }
+
     //   NRF_POWER->SYSTEMOFF=1;
 }

targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF51/us_ticker.c

@@ -44,7 +44,7 @@
 #include "nrf_drv_common.h"
 #include "mbed_critical.h"
 
-static bool us_ticker_initialized = false;
+bool us_ticker_initialized = false;
 
 /* us ticker is driven by 1MHz clock and counter length is 16 bits. */
 const ticker_info_t* us_ticker_get_info()