S32K14x SIRC monitoring needed?

[Xtian]

Hello, 

Can you help clarify the following question related to S32K144 ? 

S32K14x has a system OSC monitor, my understanding is that the SIRC is used to monitor the SOSC. 

The question is : what happens if SIRC fails? will this monitor flag an error ? I would like to think yes ? 

Is there a need to also monitor SIRC during startup and runtime? 

What is the recommended method for monitoring SIRC? I suppose comparing two timer values driven by different clock sources?  

What is the use then of the SIRCVLD bit ? I suppose it is not enough to look at this bit to determine if SIRC  is in the good range of values? 

Thanks for the support, 

Christian

[Xtian]

Many thanks for the support. 

[Yashwant_Singh]

Hi Christian,

Please find answers to your questions below:

1. No the SOSC monitor cannot be relied upon to detect the SIRC failures since SIRC is itself the reference clock. If a reference clock is outside operating parameters, then monitor behavior cannot be guaranteed.

2. Since SIRC is serving as the reference for a safety mechanism it is a source of latent faults only and hence it is recommended to check it at startup only. Quite likely the check of safety mechanisms in itself can check the availability of SIRC.

3 and 4. Checking the SIRCVLD bit is sufficient for running a startup check on the SIRC Clock. However, for a runtime check the SIRCVLD bit cannot be relied upon as it gets latched after startup. If really required as per the customer's analysis, then for a runtime check they may make use of timers running on different clock as you described.

Thanks!

-Yashwant