RTC Accuracy issue

[PG26]

Hello,

we are working on new release of STM32WL "STM32Cube_FW_WL_V1.3.0". release which has introduced changes in RTC driver which we believe is fixed for the issue (RTC loosing time issue STMicroelectronics/STM32CubeH7#24 )

But, after running RTC overnight we have seen RTC issue is still persist in different manner this time RTC is increasing time

Test Start time : 17:55:56, UTC time 1670415956

Test End Time: 9:48:00, UTC time 1670473080, (57124 Seconds)

Difference of UTC time should be : 57124 (1670473080 - 1670415956)

But, From attached logs we can see Test End time is 9:48:00 and total seconds are 57135s837 (check last line in logs).

RTC had generated 57135s837 seconds instead of 57124 Seconds.

So, 57135 - 57124 = 11 Seconds are increased in actual time

RTCTestLogs.txt

RTC Driver.zip

Driver files are also attached for more details.

Can someone please explain how to fix this?

[waclawek.jan]

LSE oscillator may be designed improperly and run at higher than expected frequency, or it may be influenced by high-current adjacent signals.

Read AN2867.

JW

[Piranha]

So it's slower by 193 ppm. That can easily be because of too much load capacitance for a crystal.

[AScha.3 · Accepted solution]

no, this crystal is running 193ppm too fast !

means: missing or wrong (too small) load capacitors.

check data sheet of the crystal and adjust caps to this.

read:

https://www.st.com/resource/en/application_note/cd00221665-oscillator-design-guide-for-stm8afals-stm32-mcus-and-mpus-stmicroelectronics.pdf

[PG26]

we have made changes in capacitance and now with release v1.3.0 module is providing correct time.

we have tested continuously 4 days and haven't seen any missing seconds on logs. thank you guys for the suggestion and quick support