STM32L151 RTC Alarm interrupt

Question

I am having problem with RTC alarm interrupt of STM32L151. I want my program to go to RTC alarm interrupt every second but it does not work. My main funtion:

int main(void)
{
  HAL_Init();
  SystemClock_Config();
  MX_GPIO_Init();
  MX_IWDG_Init();
  MX_RTC_Init();
  MX_SPI1_Init();
  MX_USART1_UART_Init();

  __HAL_RTC_ALARM_ENABLE_IT(&hrtc, RTC_IT_ALRA);

  while (1)
  {

  }
}

Function configures RTC: MX_RTC_Init():

void MX_RTC_Init(void)
{
  RTC_TimeTypeDef sTime;
  RTC_DateTypeDef sDate;
  RTC_AlarmTypeDef sAlarm;

  hrtc.Instance = RTC;
  hrtc.Init.HourFormat = RTC_HOURFORMAT_24;
  hrtc.Init.AsynchPrediv = 127;
  hrtc.Init.SynchPrediv = 255;
  hrtc.Init.OutPut = RTC_OUTPUT_DISABLE;
  hrtc.Init.OutPutPolarity = RTC_OUTPUT_POLARITY_HIGH;
  hrtc.Init.OutPutType = RTC_OUTPUT_TYPE_OPENDRAIN;
  HAL_RTC_Init(&hrtc);

  sTime.Hours = 0x14;
  sTime.Minutes = 0;
  sTime.Seconds = 0;
  sTime.TimeFormat = RTC_HOURFORMAT12_AM;
  sTime.DayLightSaving = RTC_DAYLIGHTSAVING_NONE;
  sTime.StoreOperation = RTC_STOREOPERATION_RESET;
  HAL_RTC_SetTime(&hrtc, &sTime, FORMAT_BCD);

  sDate.WeekDay = RTC_WEEKDAY_WEDNESDAY;
  sDate.Month = RTC_MONTH_AUGUST;
  sDate.Date = 0x24;
  sDate.Year = 0x16;

  HAL_RTC_SetDate(&hrtc, &sDate, FORMAT_BCD);

    /**Enable the Alarm A 
    */
  sAlarm.AlarmTime.Hours = 0;
  sAlarm.AlarmTime.Minutes = 0;
  sAlarm.AlarmTime.Seconds = 0;
  sAlarm.AlarmTime.TimeFormat = RTC_HOURFORMAT12_AM;
  sAlarm.AlarmTime.DayLightSaving = RTC_DAYLIGHTSAVING_NONE;
  sAlarm.AlarmTime.StoreOperation = RTC_STOREOPERATION_RESET;
  sAlarm.AlarmMask = RTC_ALARMMASK_SECONDS;
  sAlarm.AlarmDateWeekDaySel = RTC_ALARMDATEWEEKDAYSEL_DATE;
  sAlarm.AlarmDateWeekDay = 1;
  sAlarm.Alarm = RTC_ALARM_A;
  HAL_RTC_SetAlarm_IT(&hrtc, &sAlarm, FORMAT_BCD);

}

I created project using CubeMX. Do you have any idea or advice for me? Thank you

Answer 1

If a field is masked, then that won't be compared when checking alarm date. So when you mask SECONDS, then only the DAY, HOUR and MINUTE fields will be compared. The proper way of achieving 1 second interrupts with RTC is to use all alarm mask because this way none of the fields are compared and when the RTC increments the SECOND field an alarm interrupt will be generated.

sAlarm.AlarmMask = RTC_ALARMMASK_ALL;

Also all of this are described by ST in their Using the hardware real-time clock (RTC) in STM32 F0, F2, F3, F4 and L1 series of MCUs application note.

This is a very convenient solution as you do not have to reset the alarm after all interrupts.