[Linuxptp-users] Measure the accuracy of system time respect to the PHC time

[Ledda W. E. <Wil...@it...>]

Hi all,
I need to measure the accuracy of the system time respect to the time from the PHC. With the two clock synchronize with phc2sys I've tried the following

clock_gettime(CLOCK_REALTIME, &ts)
clock_gettime(phc, &tphc)
accuracy = ts - tphc

In this way the accuracy is always about 3 us.

I'm a bit confused about the difference between this value and the offset reported from phc2sys (always under 1us). I have seen the code in order to find the reason of this difference and I understand that the offset is calculated reading the PHC between two system time and assuming that the PHC is exacltly in the half between them.

My question is: which is the best way to measure the accuracy between the system time and the PTP time?