[NRF52840]: fix:

- rtc overflow-while-set-timestamp issue
- timer has a race condition

targets/TARGET_NORDIC/TARGET_NRF5_SDK13/us_ticker.c

@@ -55,32 +55,36 @@
 bool              m_common_rtc_enabled   = false;
 uint32_t volatile m_common_rtc_overflows = 0;
 
+__STATIC_INLINE void rtc_ovf_event_check(void)
+{
+    if (nrf_rtc_event_pending(COMMON_RTC_INSTANCE, NRF_RTC_EVENT_OVERFLOW)) {
+        nrf_rtc_event_clear(COMMON_RTC_INSTANCE, NRF_RTC_EVENT_OVERFLOW);
+        // Don't disable this event. It shall occur periodically.
+
+        ++m_common_rtc_overflows;
+    }
+}
+
 #if defined(TARGET_MCU_NRF51822)
 void common_rtc_irq_handler(void)
 #else
 void COMMON_RTC_IRQ_HANDLER(void)
 #endif
 {
-    if (nrf_rtc_event_pending(COMMON_RTC_INSTANCE, US_TICKER_EVENT))
-    {
+
+    rtc_ovf_event_check();
+
+    if (nrf_rtc_event_pending(COMMON_RTC_INSTANCE, US_TICKER_EVENT)) {
         us_ticker_irq_handler();
     }
 
 #if DEVICE_LOWPOWERTIMER
-    if (nrf_rtc_event_pending(COMMON_RTC_INSTANCE, LP_TICKER_EVENT))
-    {
+    if (nrf_rtc_event_pending(COMMON_RTC_INSTANCE, LP_TICKER_EVENT)) {
 
         lp_ticker_irq_handler();
     }
 #endif
 
-    if (nrf_rtc_event_pending(COMMON_RTC_INSTANCE, NRF_RTC_EVENT_OVERFLOW))
-    {
-        nrf_rtc_event_clear(COMMON_RTC_INSTANCE, NRF_RTC_EVENT_OVERFLOW);
-        // Don't disable this event. It shall occur periodically.
-
-        ++m_common_rtc_overflows;
-    }
 }
 
 // Function for fix errata 20: RTC Register values are invalid
@@ -168,13 +172,37 @@ void common_rtc_init(void)
     m_common_rtc_enabled = true;
 }
 
+__STATIC_INLINE void rtc_ovf_event_safe_check(void)
+{
+    core_util_critical_section_enter();
+
+    rtc_ovf_event_check();
+
+    core_util_critical_section_exit();
+}
+
+
 uint32_t common_rtc_32bit_ticks_get(void)
 {
-    uint32_t ticks = nrf_rtc_counter_get(COMMON_RTC_INSTANCE);
+    uint32_t ticks;
+    uint32_t prev_overflows;
+
+    do {
+        prev_overflows = m_common_rtc_overflows;
+
+        ticks = nrf_rtc_counter_get(COMMON_RTC_INSTANCE);
         // The counter used for time measurements is less than 32 bit wide,
         // so its value is complemented with the number of registered overflows
         // of the counter.
         ticks += (m_common_rtc_overflows << RTC_COUNTER_BITS);
+
+        // Check in case that OVF occurred during execution of a RTC handler (apply if call was from RTC handler)
+        // m_common_rtc_overflows might been updated in this call.
+        rtc_ovf_event_safe_check();
+
+        // If call was made from a low priority level m_common_rtc_overflows might have been updated in RTC handler.
+    } while (m_common_rtc_overflows != prev_overflows);
+
     return ticks;
 }
 
@@ -213,6 +241,7 @@ void common_rtc_set_interrupt(uint32_t us_timestamp, uint32_t cc_channel,
     uint32_t compare_value =
         (uint32_t)CEIL_DIV((timestamp64) * RTC_INPUT_FREQ, 1000000);
 
+    core_util_critical_section_enter();
     // The COMPARE event occurs when the value in compare register is N and
     // the counter value changes from N-1 to N. Therefore, the minimal safe
     // difference between the compare value to be set and the current counter
@@ -226,6 +255,7 @@ void common_rtc_set_interrupt(uint32_t us_timestamp, uint32_t cc_channel,
 
     nrf_rtc_cc_set(COMMON_RTC_INSTANCE, cc_channel, RTC_WRAP(compare_value));
     nrf_rtc_event_enable(COMMON_RTC_INSTANCE, int_mask);
+    core_util_critical_section_exit();
 }
 //------------------------------------------------------------------------------