[ntp:questions] best jitter on qnx always = 0.977

Dave Hart hart at ntp.org
Tue May 10 17:09:44 UTC 2011

On Tue, May 10, 2011 at 16:22 UTC, Николай Орехов <nowhere at mail.ru> wrote:
> Why on QNX I always get the same best jitter 0.977 even on PPS ?

I see the same thing on a laptop running Windows Vista.  This likely
indicates ntpd measured your system clock precision as 2 ** -10
seconds, or 1/1024th of a second.  ntpd uses the precision of the
local clock as the minimum jitter, because every local timestamp
involved in its calculations is trusted only to the level of the clock

Reading the clock probably costs less than a millisecond on your
system, but the value read changes only once per millisecond.  If you
could convince QNX to provide a higher-precision system clock, you can
drive the precision down and bring your jitter figures with it.

Dave Hart

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