On 2013-11-22, [email protected] <[email protected]> wrote: > I have just written a PHC driver for NTP and tested it on this system: > Supermicro SYS-50150EHF-D525 which has a pair of Intel 82574L NICs which > have IEEE 1588 hardware-based timestamping. I'm using NTP dev 4.2.7p397 on > Linux kernel 3.12 with linuxptp. One of the PHCs is sync'd via PTP to an FEI > Zyfer Gsync GrandMaster, which is in turn synced via 5MHz to the USNO Master > Clock #2. > > I'm running ptp4l to sync PHC1 to the GrandMaster. Then NTP is reading the > refclocks PHC0, PHC1 and an NTP server on the LAN ptp2: > > ntpq -p > remote refid st t when poll reach delay offset jitter >============================================================================== > +PHC(0) .PTP. 0 l 15 16 377 0.000 0.000 0.000 > *PHC(1) .PTP. 0 l 2 16 377 0.000 -0.001 0.000 > +ptp2 .IRIG. 1 u 38 64 377 0.123 0.018 0.007 > > After about 15 hours the loopstats shows a s.d. of +/- 0.579 microsec with > peak-peak 2.52 microsec (3,073 points). Very superb. > > However, it took fully 75 minutes at start to converge. It took that long to > remove 20ms of phase error. I have never seen such a slow convergence. Very > smooth too. I have tested the NMEA/ATOM drivers on this system and the > convergence was the normal few minutes. Any suggestions? Can email plots.
David Mills has always stated that rate of convergence is not a problem he cares about at all. Stability of running is. ntpd is NOT designed to converge quickly. If you want faster convergence ( and better clock discipline although possibly slightly higher drift noise) use chrony. Certainly a SD of .5us is far better than any standard PC can get from an interrupt driven stratum 0 source due to interrupt latency fluctuations. I am surprized you can get such good results from a NIC based solution (even with hardware timestamping). > > Rich Schmidt > Time Service Dept > US Naval Observatory _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
