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This could lead to an about >> 1-second error in the reported time. > > Have you checked whether the hardware protects against this (i.o.w. the > hardware latches the PTP_STSR value when PTP_STNSR is read, or vice > versa? Several PTP devices I've looked at do this to allow consistent > reading. > It doesn't. I was able to observe inconsistent values doing reads in either order, and we had already observed the issue with that same IP on another device (Cortex-M based, not running Linux). It's not easy to reproduce, the time window is small, but it's there.