[ntp:questions] Slow convergence loopstats (but nice results)

schmidt.rich at gmail.com schmidt.rich at gmail.com
Fri Nov 22 16:19:11 UTC 2013

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..

Rich Schmidt
Time Service Dept
US Naval Observatory

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