On Tue, Jul 02, 2019 at 09:31:44AM -0700, Richard Cochran wrote: > On Tue, Jul 02, 2019 at 09:36:50AM +0200, Miroslav Lichvar wrote: > > So, with two > > directly connected I210s (short cable) the measured delay should be > > close to zero. > > That is true of any two devices, since the tx/rx asymmetry cancels out > (even without any corrections applied).
The error in the measured offset cancels out between any two identical NICs, but the measured PTP delay is a sum of the TX and RX timestamping errors (and the delay in the cable). For example between two I350s on 1Gb I see a delay of 507 ns. An offset I measured between an I210 (using the igb compensation) and I350 in the same computer over PCIe is about 240 ns, so the TX/RX error of the I350 seems to be very asymmetric too. -- Miroslav Lichvar _______________________________________________ Linuxptp-users mailing list Linuxptp-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-users
