> From: "David McConnell" <[EMAIL PROTECTED]> > Date: Tue, 30 Sep 2008 14:04:18 +0100 > Sender: [EMAIL PROTECTED] > > > Hi > > We are using Linux ntpd with GPS/PPS reference clock to discipline the time > on our systems. > > Our application requires good time accuracy (better than 5ms) but it also > needs to get there quickly (as quickly as possible, but ideally taking no > more than about 15 minutes). > (The Linux/ntpd is running on a remote embedded device that is frequently > restarted - possibly once a day or so - so we cant wait hours for > convergence). > > Currently ntpd can take hours to achieve the desired acuracy. > > So, the question is simple - is there any way to significantly speedup the > convergence of ntpd (using GPS/PPS reference clock)? > > We would be prepared to compromise somewhat on accuracy and jitter. > (Currently accuracy and jitter values are excellent with jitter as low as 1 > microsecond and accuracy better than 10 uS but it can take a day or two to > get there). > > It does not seem unreasonable to expect that the ntpd could achieve the > required accuracy within 15 minutes or so - but nothing we have tried seems > to work. > Have tried modifying some of the tinker values, but we dont really > understand what they all do - and have not really had any success. > > So to summarise: > > 1) Is it possible to speedup ntpd convergence (using GPS/PPS reference > clock)? > 2) If so, how - and what are the tradeoffs?
Sorry for the dup for everyone on the mailing list, but I need to send it unsigned to make it to the news group. Most important is to start ntpd at boot time with the -g option so that it will immediately set the time. Then adjust your ntp.conf to set the maxpoll and minpoll to 4 for your reference clock. "minpoll 4 maxpoll 4" This will get the time synced to close to correct, hopefully a few microseconds, within a couple of minutes, depending on your hardware. -- R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: [EMAIL PROTECTED] Phone: +1 510 486-8634 Key fingerprint:059B 2DDF 031C 9BA3 14A4 EADA 927D EBB3 987B 3751 --==_Exmh_1222806547_81119P Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (FreeBSD) Comment: Exmh version 2.5 06/03/2002 iD8DBQFI4owTkn3rs5h7N1ERAmQBAJ4hJZT+g/g867Jcijg6bPrhrzT9AQCeN+5k Orv1xQK+MBGU7BWQ8YXnhio= =LqU7 -----END PGP SIGNATURE----- --==_Exmh_1222806547_81119P-- _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
