Hi everyone,
I am using a STM32H563RG and I need the RTC to work even if the VDD is powered off. To do that, I am plugging a battery on the VBAT pin to power the RTC and the Backup domain. But I tested it and it seems the RTC is stopped and the backup domain is cleared when VDD is powered off.
Here is my initialisation code :
/* Configure the system clock */
SystemClock_Config();
/* USER CODE BEGIN SysInit */
/* USER CODE END SysInit */
/* Initialize all configured peripherals */
MX_GPIO_Init();
MX_GPDMA1_Init();
MX_ICACHE_Init();
MX_CRC_Init();
MX_SPI1_Init();
MX_TIM3_Init();
//MX_RTC_Init();
MX_ADC1_Init();
MX_ADC2_Init();
MX_TIM2_Init();
MX_FileX_Init();
MX_IWDG_Init();
MX_TouchGFX_Init();
/* USER CODE BEGIN 2 */
LL_PWR_EnableBkUpRegulator();
LL_PWR_EnableBkUpAccess();
if(LL_RTC_BKP_GetRegister(RTC,LL_RTC_BKP_DR0) == 0x32F2){ //Read Backup register to see if it was previously written
RTC_Datas.RTC_initialized = 1; //Set flag
GPIO_Set(Led_orang); //Turn Orange LED On
}
else{ //If not previously written
RTC_Datas.RTC_initialized = 0; //Clear flag
MX_RTC_Init(); //Call RTC_Init() to initialise RTC
}
RTC_Datas.Jour = __LL_RTC_CONVERT_BCD2BIN(LL_RTC_DATE_GetDay(RTC)); //Read day
RTC_Datas.Mois = __LL_RTC_CONVERT_BCD2BIN(LL_RTC_DATE_GetMonth(RTC)); //Read month
RTC_Datas.Annee = __LL_RTC_CONVERT_BCD2BIN(LL_RTC_DATE_GetYear(RTC)) + 2000; //Read year
RTC_Datas.Minute = __LL_RTC_CONVERT_BCD2BIN(LL_RTC_TIME_GetMinute(RTC));//Read minutes
RTC_Datas.Heure = __LL_RTC_CONVERT_BCD2BIN(LL_RTC_TIME_GetHour(RTC)); //Read hours
The value 0x32F2 is written in the BKR0 backup register by the MX_RTC_Init() function. It should stay written in it even if there is a µC reset (with VBAT at 3,3V). I check if the RTC was previously initialised by reading this backup register : if I read 0x32F2, it means it was initialised and a Orange LED is turned ON. However, after a reset (performed by the VDD being powered off then powered on right away), the Orange LED doesn't turn ON and the RTC values are reinitialised.
What I made sure of :
- RTC is clocked on LSE
- LSE drive capabilty is HIGH
- TAMP secure zone is deactivated
- VBAT stays at approx. 3V3 during reset
- LSE still on after reset
- BREN bit of PWR->BDCR is set (to enable backup regulator)
It seems there is no Backup domain reset happening since the RTCSEL bit field of RCC->BDCR stays at 1 after reset ( it would be equal to 0 after a bakcup domain reset).
I therefore have three questions :
1) Are the RTC values saved in the backup domain or it is two different things ?
2) Is my test method correct to prove the Backup register is cleared ?
3) What could clear the Backup register and the RTC values reset ?
