STM32WB55 : Detecting All Types of Clock Errors (Beyond CSS)

[FGron.1]

Hello,

I'm currently working on a medical project based on the STM32WB55. One of our key safety requirements is to be able to detect a maximum of clock-related error, including:

• Complete clock failures

• Missed or irregular clock ticks

• Frequency variations or drift

I’ve already enabled the Clock Security System (CSS) for both HSE and LSE, but it seems that CSS only detects complete clock failures (i.e., when the oscillator stops entirely). It does not catch more subtle issues like missed clock ticks or frequency deviations.

My question is:
Are there any known techniques or best practices to detect a wider range of clock anomalies on STM32WB55?

Any insights, suggestions, or references would be greatly appreciated.

Thanks in advance!

[TDK · Accepted solution]

Start a timer using HSE and another using LSE and periodically compare them to ensure the ratio is as expected. This will catch frequency deviations of one vs the other.