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CRS SYNC setup with LSE and CubeMX puzzle

Senior III

I try to setup CRS SYNC setup with LSE using the latest CubeMX.
It appears that when CRS SYNC with Source LSE is selected, LSE does not get initialized unless RTC is active as well and its clock source is set to LSE. E.g crystal drive level option does not show up, generated source code does not activate LSE, but __HAL_RCC_CRS_CLK_ENABLE() and HAL_RCCEx_CRSConfig() functions are being called. Is there any reason for that?

What is more, for STM32U5Ax CubeMX allows to select USB as CRS source while according to RM0456, Table 122 that is not an option.




ST Employee

Hello @TDJ and welcome to the ST Community 😊.

Thank you for your post. I'm checking this internally and I will get back to you as soon as possible.

Best regards.


To give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

Senior III

@STTwo-32 Thank you for looking into this. This actually may be more serious bug than it appears to be.
Enabling CRS SYNC does not actually enable it. I realized that after a few hours of investigating why ADC clock was slightly off when it was supposed to be LSE synced. I think it may also seriously impair USB reliability.