[ntp:questions] ntpd - gpsd communication

Gary E. Miller gem at rellim.com
Mon Jun 8 22:25:09 UTC 2020

Yo Steven!

On Mon, 8 Jun 2020 17:06:55 -0500
Steven Sommars <stevesommarsntp at gmail.com> wrote:

> The off by N-second errors are often seen soon after NTP server
> initialization.

This is common to all GPS based NTP servers.  It is distinct from
long lasting off-by one errors that one version of gpsd could fall
victimm to.

When a GPS starts up, it often uses the value for the current leap
second stored in the firmware.  By "leap second" I mean the correction
from GPS tim to UTC time which is always in integer seconds.

This stored leap second is often off by one or two seconds, or more,
for a while.

After receiving the Almanac, which can take up to 25 minutes on some
older GPS, the current leap second offset is known.  But now ntpd is
set in its ways, and will take a while to slew to the correct time.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588

	    Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin
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