How do I read the RTC on the STM32L433 after power up.

Scott Dev · ‎2018-12-24

Hi

I am using the RTC on the STM32L433 with battery backup. After the date/time been set and running , then either processor reset or repoert the unit the date/time resets to the default time. As it happens even after reset (power not disconnected) I know it isnt a repower issue.

Basically as I have a battery backup, I want to not set the date/time after repowering (or resetting) the processor , but simply keep the same date and time. How is this done?

Thanks

Scott

waclawek.jan · ‎2018-12-26

Simply by not doing anything.

Ditched Cube yet?

JW

Scott Dev · ‎2018-12-27

Thanks, that worked, cheers. I thought it still had to be reinitialised.

I only use Cube to do the clock initialisation, but the rest by simply programming the registers. Still getting used to the stm32 , but getting there 🙂

Scott

Scott Dev · ‎2019-01-11

With the battery backup the time is kept up to date, but the date isnt. Anyone know why this is?

Regards

Scott

waclawek.jan · ‎2019-01-11

post details

Scott Dev · ‎2019-01-11

Sorry , I thought I posted the below...

After power up I check the backup register to see if previous been setup, if its not, then initialise RTC. Else read date and time.

Regards

Scott

//Routine for initialising RTC after power up

void InitRTC(void)

{

if((RCC->APB1ENR1 & RCC_APB1ENR1_PWREN)==0)

RCC->APB1ENR1 |= RCC_APB1ENR1_PWREN;

//check to see previously set

if(RTC->BKP0R!=0x1954)

{

//nope

if((PWR->CR1 & PWR_CR1_DBP) ==0)

{

PWR->CR1 |= PWR_CR1_DBP;

while((PWR->CR1 & PWR_CR1_DBP)==0);

}

RCC->BDCR &= ~(RCC_BDCR_LSEON | RCC_BDCR_LSEBYP);

RCC->BDCR |= RCC_BDCR_BDRST;

RCC->BDCR &= ~RCC_BDCR_BDRST;

while((RCC->BDCR & RCC_BDCR_LSERDY)==0)

RCC->BDCR |= RCC_BDCR_LSEON;

RCC->BDCR &= ~RCC_BDCR_RTCSEL;

RCC->BDCR |= RCC_BDCR_RTCSEL_0;

RCC->BDCR |= RCC_BDCR_RTCEN;

RTC->WPR = 0xCA;

RTC->WPR = 0x53;

RTC->ISR |= RTC_ISR_INIT;

if((RTC->ISR & RTC_ISR_INITF) == 0)

RTC->ISR = (uint32_t)0xFFFFFFFFU;

while((RTC->ISR & RTC_ISR_INITF) == 0);

while((RTC->ISR & RTC_ISR_ALRAWF)==0);

RTC->PRER = 0x007F00FF;

//set initialise date/time

RTC->TR= 0U<<22 | 1U <<20 | 5U<<16 | 1U<<12 | 1U<<8 |1<< 4 | 5;

RTC->DR= 1U<<20 | 8U <<16 | 1U << 13| 1U<<12 | 2U<<8 | 6U<<4 | 4;

RTC->ISR &=~ RTC_ISR_INIT;

RTC->WPR = 0xFF;

RCC->BDCR |= RCC_BDCR_RTCEN;

RTC->BKP0R=0x1954;

}

while((RTC->ISR & RTC_ISR_RSF)==0);

ReadTime();

ReadDate();

}

void ReadTime(void)

{

Tme.Sec=(((RTC->TR & 0x7f) >> 4)*10)+(RTC->TR & 0xf);

Tme.Min=((RTC->TR & 0x7f00) >> 8);

Tme.Min=(((Tme.Min & 0x7f)>>4)*10)+(Tme.Min & 0xf);

Tme.Hour=((RTC->TR & 0x7f0000) >> 16);

Tme.Hour=(((Tme.Hour & 0x7f)>>4)*10)+(Tme.Hour & 0xf);

Tme.Time=Tme.Hour*100+Tme.Min;

Tme.FullTime=(long)Tme.Hour*10000+(long)Tme.Min*100+(long)Tme.Sec;

}

void ReadDate(void)

{

Dte.Year=((RTC->DR >> 20)*10) + ((RTC->DR >>16) & 0xf);

Dte.Month=((RTC->DR >> 12) & 1)*10 + ((RTC->DR >>8) & 0xf);

Dte.Day=((RTC->DR >> 4) & 3)*10 + (RTC->DR & 0xf);

Dte.Date=((long)Dte.Year+2000)*10000+(long)Dte.Month*100+(long)Dte.Day;

}

waclawek.jan · ‎2019-01-11

> time is kept up to date, but the date isnt

What exactly are the symptoms and how exactly do you observe them?

While this shouldn't cause problems you describe, I would recommend against multiple reading of the RTC_TR and RTC_DR registers. Read them once into a temporary variable to be dissected later. Mind the order of reading if BYPSHAD=0 ( To ensure consistency between the 3 values, reading either RTC_SSR or

RTC_TR locks the values in the higher-order calendar shadow registers until RTC_DR is

read.)

JW

Scott Dev · ‎2019-01-11

After I read the date/time into variables, I display them on a terminal application. Every few seconds I display date/time on the terminal. I never copied the date/time into variables as I am still learning the STM32 processor (previously a freescale, or NXP now person), so this is just temporary code just till I get used to each module. I switch off the power and after a few days, re-apply it , just to see the time is still accurate, but the date hasnt changed. Which I dont understand. I am not sure if I am doing anything wrong, but must be somewhere :(

Regards

Scott

waclawek.jan · ‎2019-01-11

Humm this is weird and I never experienced anything like this.

Can you please now read out the RTC registers using a debugger and post them, pointing out what is the expected value of DR?

JW

Scott Dev · ‎2019-01-15

It worked this time, this is weird. I couldnt see why it wouldnt , but I am sure it didnt the other day. I have currently set it, and will test it every few days to make sure all is what it should be. I will blame it on my New Year , we like to celibrate it here in Scotland ...

Scott