Hello Sanjay.
“Richard had suggested that this could be done by feeding GPS PPS into the NIC” I have modified the FEC driver for iMX6 to bring in the GPS-PPS. I’m able to track GPS by +/- 25ns (given that the GPS receiver is only that stable) Using a modified version of phy2sys to keep /dev/ptp0 in sync From: Sanjay Bhandari [mailto:san...@ziffusion.com] Sent: Dienstag, 11. Juni 2019 14:31 To: Miroslav Lichvar Cc: linuxptp-devel@lists.sourceforge.net Subject: Re: [Linuxptp-devel] support for chrony like refclock SOCK > How is timestamping GPS PPS different from timestamping external events? If > the driver could provide this feature using the existing PHC API, I think that would be the best approach. It's not. I am saying that to train the PHC to GPS time, we need to timestamp the GPS PPS with the PHC clock (so we can get the offset to train the PHC). In the other thread (https://is.gd/qyYHDt) Richard had suggested that this could be done by feeding GPS PPS into the NIC - IF the NIC was capable of timestamping external events like this. I was saying that some NICs can't do this, so it may be done elsewhere (like we do in our FPGA). In which case it would help to have a mechanism being discussed in this thread, to feed the samples into ptp4l or phc2sys to train the PHC. On Tue, Jun 11, 2019 at 8:47 AM Miroslav Lichvar <mlich...@redhat.com> wrote: On Mon, Jun 10, 2019 at 08:17:05AM -0400, Sanjay Bhandari wrote: > Has it been considered adding a chrony like refclock SOCK interface ( > https://is.gd/skln7i) to either ptp4l or phc2sys, where samples could be > fed from an external source like the GPS (or other) to set the PHC? What > are the pros and cons to this? There is an option in phc2sys to forward the measurements to an external process using the NTP SHM refclock interface, so it would make some sense to add an option to read for the measurements. Instead of the chrony SOCK or NTP SHM refclock, I'd prefer something simpler like reading pairs of offset and delay in a text form from the standard input. > But some PHCs do not support timestamping external events. In our case, for > example, we are timestamping GPS PPS by the PHC clock in the hardware > (FPGA) How is timestamping GPS PPS different from timestamping external events? If the driver could provide this feature using the existing PHC API, I think that would be the best approach. -- Miroslav Lichvar
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