Hi, We had a similar issue where our time source was sending out ARB time rather than PTP time. The Hardware timestamped node was always out by the TAI / UTC offset (36 seconds at the moment) from the software timestamped node.
When it sends ARB (there is a flag in the PTP packet), it ends up sending the UTC time which appears to get interpreted by the hardware timestamping system as TAI, whereas the software system correctly picks it as UTC. When it sends PTP time, it has to be TAI, so both interpret it correctly. Once we managed to get the timesource to output PTP time (a Symmetricom source that wouldn't send PTP time unless it has a valid GPS lock) the problem went away. Cheers, Gethyn -----Original Message----- From: Miroslav Lichvar [mailto:mlich...@redhat.com] Sent: 14 July 2017 08:05 To: Petr Kulhavy Cc: linuxptp-users@lists.sourceforge.net Subject: Re: [Linuxptp-users] UTC offset On Fri, Jul 14, 2017 at 12:32:58AM +0200, Petr Kulhavy wrote: > I have two devices running linuxptp as slaves with the same > configuration, the only difference is that one uses SW timestamping > and the other HW timestamping. > Both report the same GM in `pmc GET TIME_STATUS_NP`, but they have a > different time, approximately the 36 seconds in difference. > > Generally I would expect both slaves to behave the same if they have > the same configuration and use the same GM. > What is wrong? What do I have to do in order to make them both have > the same time as the master? As you observed, the difference is in the timestamping. With HW timestamping ptp4l keeps the PTP clock in TAI and it's up to phc2sys to convert it to UTC when it synchronizes the system clock. With SW timestamping ptp4l synchronizes the system clock, so it must convert it to UTC. I guess it would be possible to implement a mode where ptp4l keeps the PTP clock in UTC. I'm not sure how useful that would be. -- Miroslav Lichvar ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Linuxptp-users mailing list Linuxptp-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-users The data contained in, or attached to, this e-mail, may contain confidential information. If you have received it in error you should notify the sender immediately by reply e-mail, delete the message from your system and contact +44 (0) 3301235850 (Security Operations Centre) if you need assistance. Please do not copy it for any purpose, or disclose its contents to any other person. An e-mail response to this address may be subject to interception or monitoring for operational reasons or for lawful business practices. (c) 2017 Rolls-Royce plc Registered office: 62 Buckingham Gate, London SW1E 6AT Company number: 1003142. Registered in England. ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Linuxptp-users mailing list Linuxptp-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-users
