WB5MMG RTC Inaccurate

[Csu.11]

WB5MMG RTC Inaccurate, RTC increase by 1s requires 10s or more in reality.

32.768 LSE has been used.

 	RTC_TimeTypeDef sTime = {0};
 	HAL_RTC_GetTime(&hrtc, &sTime, RTC_FORMAT_BIN);
 	RTC_DateTypeDef sDate = {0};
 	HAL_RTC_GetDate(&hrtc, &sDate, RTC_FORMAT_BIN);
 
 	Send_Log("%d %d %d %d% d %d", sDate.Year,sDate.Month,sDate.Date,sTime.Hours,sTime.Minutes,sTime.Seconds);

[Peter BENSCH]

The RTC is just as precise as its settings and clock sources. But since you haven't added any details about your implementation (crystal type, load capacities, layout, LSE settings, clock tree, HAL/LL/direct programming etc.), little information can be given.

Regards

/Peter

[Csu.11]

Thank you for your reply, I have added some information about my settings.

[Peter BENSCH]

OK, where did you assign which value to

• CFG_RTC_ASYNCH_PRESCALER and
• CFG_RTC_SYNCH_PRESCALER?

What are your RCC settings for LSE?

[Csu.11]

RCC settings for LSE is here. I have tried every option of LSE Driver, but it didn’t work.CFG_RTC_ASYNCH_PRESCALER and

CFG_RTC_SYNCH_PRESCALER is an option of CubeIde, and there are no other options to choose.

#define CFG_RTC_ASYNCH_PRESCALER (0x0F)
#define CFG_RTC_SYNCH_PRESCALER (0x7FFF)

 

[Peter BENSCH]

Prescalers of 0x0F = 16 (-1) and 0x7FFF = 32768 (-1) would result in 32768Hz /(2^4*2^15) = 1/16 Hz --> 16s period. It looks like this is what you see, right?
Please change the asynchronous prescaler to 128-1, i.e. 0x7F and the synchronous one to 256-1, i.e. 0xFF, to get the correct 1Hz pulses.
You can check RM0434, section 29 for more information about the RTC and the energy efficient usage of the prescalers.

[Csu.11]

According to your answer, I solved this problem smoothly, thank you very much.

[JWieb]

See Also:

https://community.st.com/s/question/0D53W00000XhmmbSAB/stm32wb-how-to-use-rtc-with-ble