[Linuxptp-users] offsetFromMaster vs. 1-PPS

[First L. <ssr...@gm...>]

Hello,

I have a system that I am using LinuxPTP with to synchronize a very simple
network. I am using Intel I210-T1 NICs, and outputting a 1-PPS signal to
validate that LinuxPTP is working well. I am trying to compare the
offsetFromMaster value in LinuxPTP and the 1-PPS signal, since they both
measure Time Error between Master and Slave, just in different ways.

In general, I'm seeing the values are relatively close to each other (they
have similar amplitudes), but in no way resemble one another. Sometimes, I
see offsetFromMaster have a large abnormal jump, which I don't see
happening at the PPS signal. I'm wondering why this is. Since I'm using HW
Timestamping, the offsetFromMaster calculation should be doing the standard
offset calculation based on the HW timestamps taken on the NIC, defined in
the spec: ((t2-t1) - (t4-t3)) / 2. And the PPS Signal is asserted once per
second based on the clock on the NIC I believe. What would cause
discrepancies between the two measurements of Time Error?

Thanks.