[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [gpsd-dev] Disturbing numbers

From: Greg Troxel
Subject: Re: [gpsd-dev] Disturbing numbers
Date: Sun, 03 Nov 2013 19:03:19 -0500
User-agent: Gnus/5.130006 (Ma Gnus v0.6) Emacs/23.4 (berkeley-unix)

Andy Walls <address@hidden> writes:

> Sounds reasonable for startup.  I wouldn't expect it at steady/stable
> state.
> ntpd prefers to slew clocks into alignment.
> system clock frequency will change, and ntpd will have to adjust it, a
> bit until your computer is thermally stable.
> Do keep in mind, that compared to a decent PPS, it is the ntpd
> disciplined system clock which is drifting.

All true, and I don't mean to contradict Andy

What I'd expect is that because the frequency error estimate that NTP
uses ("drift") isn't right when you first start NTP, there will be a
phase error that persists while the frequency is estimated.  So if your
clock is a litle slow, then it will keep getting behind, and the
positive offset will cause NTP to adjust the phase forward and also
increase the frequency offset error.  After a day or so or maybe less
the frequency estimate will be very close and there won't be a
persistent offset.  This is all normal.

Attachment: pgplcgzk4oHst.pgp
Description: PGP signature

reply via email to

[Prev in Thread] Current Thread [Next in Thread]