On Tue, Jun 04, 2019 at 01:42:35AM +0200, Mino Sharkhawy wrote: > Using this setup and plotting a histogram of the offsets measured on the > slave (between system clock and GPS reference) over two days, I noticed > that while the offsets roughly follow a normal distribution, they are > centered at around +500ns. I would've expected them to center around 0. > (See attached figure.) > > Can anyone explain what might introduce this behavior? I can't determine if > this is caused by phc2sys, by NTP, by the kernel, by PTP or by the network.
One explanation would be an asymmetry in phc2sys. Synchronizing the system clock to the PHC uses a more accurate method for measuring the offset than synchronizing the PHC to the system clock. This asymmetry was fixed only recently after linuxptp-2.0 was released. Have you tried phc2sys compiled from the latest sources in git? Another explanation might a difference in the PPS signals. Do they come from one GPS receiver, or are there two receivers (using the same model, firmware, configuration and located at the same place)? -- Miroslav Lichvar _______________________________________________ Linuxptp-users mailing list Linuxptp-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-users
