[STM32L0] Wake up Flag for RTC does not rise when an alarm occurs

[greffeb]

Hi,

I have a STM32L071 on a custom board

The code was generated with CubeMx for TrueSTUDIO.

I have an alarm set on the RTC to wake up the chip from standby mode everyday at 2 AM.

I tested it and the system does wake up ! good.

My problem is that I need to differentiate the origin of the wake up between RTC alarm and WKUP pin 1.

I check for PWR_FLAG_WU which does not give much information to differentiate the two.

My understanding from the reference manual (RM0377 DocID025942 Rev 8 p559) is that the bit ALRAF in the RTC initialization and status register (RTC_ISR) is the one that might be useful for me.

But even tho the system wakes up from RTC, the ALRAF flag is not set

same with RTC_IT_ALRA and RTC_FLAG_WUTF

Is there a way to know if the origin of wake up is the WKUP pin ?

regards,

Benjamin GREFFE.

code used to check the flags :

 if(__HAL_RTC_ALARM_GET_IT(&hrtc, RTC_IT_ALRA))
 {
	 lbWakedUpByRTC_IT = true;
 }
 if (__HAL_RTC_ALARM_GET_FLAG(&hrtc, RTC_FLAG_ALRAF))
 {
	 lbWakedUpByRTC_ALRAF = true;
 }
 if (__HAL_RTC_WAKEUPTIMER_GET_FLAG(&hrtc, RTC_FLAG_WUTF))
 {
	 lbWakedUpByRTC_WUTF = true;
 }

code to initialize the rtc

static void MX_RTC_Init(void)
{
 RTC_AlarmTypeDef sAlarm = {0};
 
 /** Initialize RTC Only 
 */
 hrtc.Instance = RTC;
 hrtc.Init.HourFormat = RTC_HOURFORMAT_24;
 hrtc.Init.AsynchPrediv = 125;
 hrtc.Init.SynchPrediv = 296;
 hrtc.Init.OutPut = RTC_OUTPUT_DISABLE;
 hrtc.Init.OutPutRemap = RTC_OUTPUT_REMAP_NONE;
 hrtc.Init.OutPutPolarity = RTC_OUTPUT_POLARITY_HIGH;
 hrtc.Init.OutPutType = RTC_OUTPUT_TYPE_OPENDRAIN;
 if (HAL_RTC_Init(&hrtc) != HAL_OK)
 {
 Error_Handler();
 }
 
 /** Enable the Alarm A
 */
 sAlarm.AlarmTime.Hours = 0x2;
 sAlarm.AlarmTime.Minutes = 0x0;
 sAlarm.AlarmTime.Seconds = 0x0;
 sAlarm.AlarmTime.SubSeconds = 0x0;
 sAlarm.AlarmTime.DayLightSaving = RTC_DAYLIGHTSAVING_NONE;
 sAlarm.AlarmTime.StoreOperation = RTC_STOREOPERATION_RESET;
 sAlarm.AlarmMask = RTC_ALARMMASK_DATEWEEKDAY;
 sAlarm.AlarmSubSecondMask = RTC_ALARMSUBSECONDMASK_ALL;
 sAlarm.AlarmDateWeekDaySel = RTC_ALARMDATEWEEKDAYSEL_DATE;
 sAlarm.AlarmDateWeekDay = 0x1;
 sAlarm.Alarm = RTC_ALARM_A;
 if (HAL_RTC_SetAlarm_IT(&hrtc, &sAlarm, RTC_FORMAT_BCD) != HAL_OK)
 {
 Error_Handler();
 }
}

code to go to sleep

	HAL_PWR_DisableWakeUpPin(PWR_WAKEUP_PIN1);
	__HAL_PWR_CLEAR_FLAG(PWR_FLAG_WU);
	HAL_PWR_EnableWakeUpPin(PWR_WAKEUP_PIN1);
	HAL_PWR_EnterSTANDBYMode();
	while (1)
	{
	 NVIC_SystemReset();
	}

[MFahl.1]

Hi, I have the same or similar problem. ALRAF is not set when returning from standby. I am on a different MCU, STM32F100.

For me all works according to the datasheets when I run in the debugger (ST-Link). However when I run outside the debugger the ALRAF bit never reads as 1. The MCU is returning (reset) perfectly from standby on RTC but I am not able to read a correct value on ALRAF.

Did you find a solution somewhere?

/Mats

[MFara.1346]

Any one found a solution for this?

[greffeb]

I have found a workaround to differentiate source of wakeup

after the  SystemClock_Config(); i clear all wakeup flags.

 /* Check and handle if the system was resumed from StandBy mode */
 if(__HAL_PWR_GET_FLAG(PWR_FLAG_SB) != RESET)
 {
 /* Clear Standby flag */
 __HAL_PWR_CLEAR_FLAG(PWR_FLAG_SB);
 }
 /* Disable all used wakeup sources: PWR_WAKEUP_PIN1 */
 HAL_PWR_DisableWakeUpPin(PWR_WAKEUP_PIN1);
 
 /* Clear all related wakeup flags*/
 __HAL_PWR_CLEAR_FLAG(PWR_FLAG_WU);

then i compare current RTC date with expected Calendar alarm

 /**** check alarm wakeup ****/
 /* read programmed alarm */
 uint32_t tmpregalarm = (uint32_t) RTC->ALRMAR;
 int alr_hour = bcd2int((uint8_t)((tmpregalarm & (RTC_ALRMAR_HT | RTC_ALRMAR_HU )) >> 16));
 int alr_min = bcd2int((uint8_t)((tmpregalarm & (RTC_ALRMAR_MNT | RTC_ALRMAR_MNU)) >> 8 ));
 int alr_sec = bcd2int((uint8_t) (tmpregalarm & (RTC_ALRMAR_ST | RTC_ALRMAR_SU )) );
 /* read current RTC */
 uint32_t tmpregrtc = (uint32_t) RTC->TR;
 int rtc_hour = bcd2int((uint8_t)((tmpregrtc & (RTC_TR_HT | RTC_TR_HU )) >> 16));
 int rtc_min = bcd2int((uint8_t)((tmpregrtc & (RTC_TR_MNT | RTC_TR_MNU)) >> 8 ));
 int rtc_sec = bcd2int((uint8_t) (tmpregrtc & (RTC_TR_ST | RTC_TR_SU )) );
 /* if current date= alarm -> alarm wakeup */
 if(alr_hour==rtc_hour && alr_min==rtc_min && alr_sec==rtc_sec){lbSystemWakedUpByRtcAlarm = true ;}
 else {lbSystemWakedUpByRtcAlarm = false;}

if true, the source of wakeup was the alarm. If false, the source of wakeup was from another source( WKUP PIN or RST in my case)

[MFara.1346]

Many thanks. Really appreciated. I also asked this question from ST if I get any different reply I will share it here for everyone to use.

[Cgelectronics]

I don't know if it is the same case for the STM32L071 as the STM32F103, but after many attempts and tests, I have opened a ticket with ST, and I've got this answer:

"It turns out that the ALRF flag (and indeed the whole register) is not kept through system reset - which occurs at wake up. Although this is not explicitly documented. The only similar flag that is kept is WUF in PWR_CSR register but this is combines wakeup from button and RTC alarm so not helpful in your case.
The solution is then the one you already applied - compare the current time to a predefined one from Flash/backup registers."

Check the following post if you have not solved this topic yet:

• STM32F103 Multiple wakeup sources detection. Unable to read RTC_CRL[ALRF] flag after reset from STBY