> From: "alkope...@googlemail.com" <alkope...@googlemail.com> > Date: Wed, 17 Dec 2008 08:09:24 -0800 (PST) > Sender: questions-bounces+oberman=es....@lists.ntp.org > > > Hi > I have 2 ntp servers running Linux with LinuxPPS patch. Number one > uses a Meinberg PCI511 v1.00 as time source, number two uses a > Meinberg GPS170PCI v1.10. > On both machines ntp is configured to use the Meinberg refclock > (127.127.8.0) and furthermore the Meinberg PPS outputs are connected > to the serial interfaces and use the atom driver (127.127.22.0). > The strange thing is, that there is always a delay of 1-4 ms between > the refclock and the pps signal. In my opinion they should arrive at > the exact same time. > > Here is an example graph of the dcf card: > http://img-up.net/img/dcf-delayY6wXrh.png > > Here is an example graph of the gps card: > http://img-up.net/img/gps-delayHbRmW6U.png > > And here the ntp conf entries: > DCF: > # meinberg dcf > server 127.127.8.0 prefer mode 2 > fudge 127.127.8.0 time1 -0.003 > fudge 127.127.8.0 refid DCFi > # meinberg dcf-pps > server 127.127.22.0 > > GPS: > # meinberg gps > server 127.127.8.0 prefer mode 7 > fudge 127.127.8.0 refid GPSi > # meinberg gps-pps > server 127.127.22.0 > > Does anybody else experience this problem or know how I can fix it? > > _______________________________________________ > questions mailing list > questions@lists.ntp.org > https://lists.ntp.org/mailman/listinfo/questions >
What you see is typical and the reason you use the PPS signal. The time to process the time string from the clock is long and fairly slow. The PPS is short and fast. As the documentation states, the PPS signal "trains" the clock. While it is normal and not a real problem, you can use a "fudge" to correct this a bit, but, as long as you leave the system up and configure it reasonably, it should work fine. You should also set the GPS and PPS servers with "minpoll 4 maxpoll 4". This will result in much faster convergence. -- R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: ober...@es.net Phone: +1 510 486-8634 Key fingerprint:059B 2DDF 031C 9BA3 14A4 EADA 927D EBB3 987B 3751
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