On Sat, Oct 08, 2022 at 04:05:17PM -0700, Richard Cochran wrote: > I read Annex B and Appendix III of T-REC-G.8275-202010, and I claim > that linuxptp already implements this functionality, even though there > is no "virtual port" explicitly modeled. > > I also read about APTS in T-REC-G.8275.2-202003. This is what I learned... > > On Mon, Jul 25, 2022 at 02:02:11AM +0000, Greg Armstrong wrote: > > > Virtual PTP Port is defined in Annex B of G.8275. It was moved to > > recommendation G.8275 since it can be used in both G.8275.1 and > > G.8275.2 Profiles. It was defined before 1588-2019 Special > > Port. There are similarities, but not the same. > > The text of Annex B is very thin indeed. I quote the meaty bits in full: > > This annex describes the model for inclusion of a unidirectional, > phase/time interface on a PTP clock. High-level principles are > introduced in this annex. > > When associated with an external input signal, a virtual PTP port > allows this external interface to participate in the PTP > protocol. As an input, this external port can participate in the > source selection with an associated virtual Erbest using the > associated virtual PTP port. > > When associated with an external output signal, a virtual PTP port > allows communication of the PTP clock information to other > equipment.
The APTS is a concept of a network that is not fully SyncE driven and may route through some time-unaware nodes. In this case the PTP quality will degrade, so to counter that there is an option to add a GNSS receiver at the T-BC. If it is functional - it will provide time downstream, however if it loses the track of time for some reason, the T-BC should automatically fall back to the time from the network. Since the GNSS itself doesn't come with any dataset attached, the virtual port concept was created. Its sole purpose is to present the BMCA with the dataset of the physical PPS+ToD signal. The way to implement would require the ts2phc to communicate with ptp4l and present the dataset configured in its config file when the signal is present, so the 1588 upstream port can go into passive state and ptp4l would send the correct dataset downstream. Whenever the PPS is not available, the dataset presented by ts2phc should change and the BMCA should kick in changing the time source in the tree. Regards Maciek _______________________________________________ Linuxptp-devel mailing list Linuxptp-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-devel
