My question is about the scenario where they do share the same hardware clock (as described in the manual).
On Wed, May 22, 2019, 3:57 PM Lynch, Mike <mike.ly...@hbm.com> wrote: > It is possible to have PTP hardware that does NOT share timestamping > hardware. In that case you must configure ptp4l to use “just a bunch of > devices” (boundary_clock_jbod) and use phc2sys (or the like) to synchronize > the independent timestamping hardware. The one platform I have experienced > this with is the Cyclone V SOC (arm). > > > > *From:* Sanjay Bhandari <san...@ziffusion.com> > *Sent:* Wednesday, May 22, 2019 2:18 PM > *To:* Richard Cochran <richardcoch...@gmail.com> > *Cc:* linuxptp-users@lists.sourceforge.net > *Subject:* Re: [Linuxptp-users] question on "-a" option in phc2sys (and > boundary clock etc.) > > > > Have a followup question on this. > > > > It says in the man page that: > > > > > When running as a boundary clock ... all of the ports share the same > hardware clock device. > > > > And then: > > > > > For this mode, the collection of clocks must be synchronized by an > external program, for example phc2sys > <https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmanpages.ubuntu.com%2Fmanpages%2Fcosmic%2Fman8%2Fphc2sys.8.html&data=01%7C01%7Cmike.lynch%40hbm.com%7C29e44de4211041057cd708d6deea64e4%7C6cce74a3397545e09893b072988b30b6%7C0&sdata=bbokgjlR%2BjMwYLylu5k%2Bc52xFBZ663k5n5pRbYiOMfw%3D&reserved=0>(8) > in "automatic" mode. > > > > I am confused about what this external program is supposed to do. If all > the ports share the same hardware clock device, then aren't these ports > synchronized already? Once ptp4l sets the PHC on a slave port, won't all > the other ports see the same exact time automatically? How can 2 clocks > that share the same hardware clock device be even out of sync? > > > > On Tue, May 21, 2019 at 12:53 AM Richard Cochran <richardcoch...@gmail.com> > wrote: > > On Mon, May 20, 2019 at 12:31:07PM -0400, Sanjay Bhandari wrote: > > > With the *-a* option, the clocks to synchronize are fetched from the > > running *ptp4l* daemon and the direction of synchronization automatically > > follows changes of the PTP port states. > > > > Is this talking about multiple PTP ports (clocks)? > > Yes. > > > Is it saying that > > phc2sys will follow the roles decided by the PTP protocol, and set the > PHC > > on ports that happen to be masters from a port that is a slave? > > You got it! > > > All I can > > think is that this applies when the node is a boundary clock. Can someone > > comment? > > Um hm. > > > How does this play with the scenario where the node is the grandmaster? > > What is the direction of time synchronization in that case? > > It picks the first interface from the ptp4l command line (or > config. file) as the master clock. > > With -r -r you can also serve CLOCK_REALTIME. > > HTH, > Richard > >
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