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<mailto: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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