> -----Original Message----- > From: Miroslav Lichvar [mailto:mlich...@redhat.com] > Sent: Thursday, April 26, 2018 12:33 AM > To: Keller, Jacob E <jacob.e.kel...@intel.com> > Cc: Cliff Spradlin <thr...@google.com>; linuxptp-users@lists.sourceforge.net > Subject: Re: [Linuxptp-users] ptp4l and SyncE > > On Tue, Apr 24, 2018 at 05:10:48PM +0000, Keller, Jacob E wrote: > > > -----Original Message----- > > > From: Miroslav Lichvar [mailto:mlich...@redhat.com] > > > Sent: Tuesday, April 24, 2018 12:16 AM > > > To: Cliff Spradlin <thr...@google.com> > > > Cc: linuxptp-users@lists.sourceforge.net > > > Subject: Re: [Linuxptp-users] ptp4l and SyncE > > > > > > I have a pair of directly connected X550 cards, which behave a bit > > > like SyncE with the frequency. Their clocks seem to be locked to each > > > other or some other common source. I'm not sure how this works and I'd > > > love to see some explanation. > > > > If it's two different X550 cards, I don't know. If it's two ports of the > > same card, > the devices *do* share the same clock source (but you can't atomically set the > registers for them, so it's not feasible to set it up as a proper boundary > clock) > > It's two different X550T cards. They have one port connected to the > same switch and one port connected directly between them. Maybe the > cards use one clock for both MAC and PHY layers? If the two ports of > one card shared the clock too, that wouldn't work with different ports > running at slightly different frequencies, right? (I don't know much > about Ethernet and whether any of this makes any sense). >
Each port uses the same clock *source*, but uses its own set of registers to tune the frequency, so each one can run independently. You can't run them as a "2 ports on the same clock" boundary clock style setup, because it is not possible to atomically set all the registers to the same values. Thus, in practice they have separate clocks, but they *do* source from the same frequency. In the case of two X550T cards, I would expect there to be *some* difference, but if the clock sources are high quality it is possible they are close enough that we can't detect any difference in them? (though, changing frequency in on PHC using the ptp API should not affect the other, unless something else is connecting them...) Thanks, Jake > -- > 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
