On 01.02.2019 16:25, Miroslav Lichvar wrote: > On Fri, Jan 18, 2019 at 03:50:51PM +0300, Artem Panfilov wrote: >> The auxiliary snapshot feature allows you to store a snapshot >> (timestamp) of the system time based on an external event. >> This feature is supported on Intel and Synopsys GMAC NICs. >> 1PPS signal could be connected as external timestamping source >> and used to estimate error. > > It's not clear to me what exactly is this supposed to do. It requires > the system clock to be specified as the source clock. Why? > > The only thing I managed to do with it is this: > # ./phc2sys -e 0 -c /dev/ptp1 -s CLOCK_REALTIME -O 0 -m > phc2sys[3070.094]: PPS is not in sync with PHC (0.940064462) > phc2sys[3071.094]: PPS is not in sync with PHC (0.940014584) > phc2sys[3072.094]: PPS is not in sync with PHC (0.940011248) > phc2sys[3073.094]: PPS is not in sync with PHC (0.939944354) > > The patch needs to update the documention and explain what is > synchronized to what in this mode. > > What I'd like to see implemented, and I'm not sure if that's what this > patch is trying to do, is synchronization of a PHC to its own PPS > input. When the PHC is synchronized to an external PPS signal, the > system clock could be synchronized to the PHC. >
Hi Miroslav, I've been meaning to ask some clarification on this patch as well, and perhaps even ask for some suggestions. I believe the typical use case is to use a GNSS module as a clock provider. NMEA data would provide absolute time of day while the servo is unlocked, and PPS signal would provide phase alignment. The issue seems to be that there is no GNSS driver in Linux that exposes the time of day as a PHC. Aditionally, the PPS signal from the GNSS module usually needs to be processed by a PHC driver belonging to an Ethernet controller (and served to userspace as extts events). Frantisek Rysanek added the same functionality a while ago in a program called i210_ext_pps (https://sourceforge.net/p/linuxptp/mailman/message/36228042/) Unfortunately it suffered of the same limitation as the currently proposed patch does: it had no standard interface over which it could collect the GNSS module's time of day. -Vladimir _______________________________________________ Linuxptp-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linuxptp-devel
