fix: RTC Alarm with Lowpower (example STM32LowPower -> TimedWakeup)

* RTC_initClock() must be called after reset of backup domain
* NVIC interrupt enable is done within RTC_StartAlarm()
  to avoid cases where alarm is pending but never cleared by ISR handler
* STM32RTC::begin() should get format parameter instead of period
* If timer is not already set, configure an arbitrary time for Lowpower usage

Signed-off-by: Alexandre Bourdiol <alexandre.bourdiol@st.com>

Author: ABOSTM

src/STM32RTC.cpp

@@ -948,7 +948,7 @@ void STM32RTC::configForLowPower(Source_Clock source)
     end();
     _clockSource = source;
     // Enable RTC
-    begin(period);
+    begin(_format);
     // Restore config
     setTime(seconds, minutes, hours, subSeconds, period);
     setDate(weekDay, day, month, years);
@@ -958,6 +958,11 @@ void STM32RTC::configForLowPower(Source_Clock source)
       enableAlarm(alarmMatch);
     }
   }
+
+  if (!isTimeSet()) {
+    // Set arbitrary time for Lowpower; if not already set
+    setTime(12, 0, 0, 0, AM);
+  }
 #endif
 }
 

src/rtc.c

@@ -355,6 +355,7 @@ bool RTC_init(hourFormat_t format, sourceClock_t source, bool reset)
 
   if (reset) {
     resetBackupDomain();
+    RTC_initClock(source);
   }
 
 #if defined(STM32F1xx)
@@ -402,9 +403,6 @@ bool RTC_init(hourFormat_t format, sourceClock_t source, bool reset)
   HAL_RTCEx_EnableBypassShadow(&RtcHandle);
 #endif
 
-  HAL_NVIC_SetPriority(RTC_Alarm_IRQn, RTC_IRQ_PRIO, RTC_IRQ_SUBPRIO);
-  HAL_NVIC_EnableIRQ(RTC_Alarm_IRQn);
-
   return reinit;
 }
 
@@ -654,6 +652,8 @@ void RTC_StartAlarm(uint8_t day, uint8_t hours, uint8_t minutes, uint8_t seconds
 
     /* Set RTC_Alarm */
     HAL_RTC_SetAlarm_IT(&RtcHandle, &RTC_AlarmStructure, RTC_FORMAT_BIN);
+    HAL_NVIC_SetPriority(RTC_Alarm_IRQn, RTC_IRQ_PRIO, RTC_IRQ_SUBPRIO);
+    HAL_NVIC_EnableIRQ(RTC_Alarm_IRQn);
   }
 }