[ntp:questions] Red Hat vote for chrony

Miroslav Lichvar mlichvar at redhat.com
Wed Dec 10 10:04:24 UTC 2014


On Tue, Dec 09, 2014 at 07:38:06PM +0000, William Unruh wrote:
> On 2014-12-09, Charles Swiger <cswiger at mac.com> wrote:
> > Well, yes.  You can get a PCI(e) card with a TCXO or OCXO and an
> > optional GPS module like the Beagle ClockCard or a SpectraCom TSync
> > for a few hundred bucks.
> >
> > That's quite a bit more than a $40 GPS puck, but these will also
> > freewheel for a lot longer before losing or gaining a second in
> > error: ~2 seconds/month if kept stable at 23C, I believe one said.
> 
> I suspect even the cheap ones can do that if kept stable at 23C. 
> (that is about 1PPM) And if you could put a fast thermal probe onto the
> crystal, you could probably do as well even in a flutuating environment
> with an addition to ntpd/chrony to use the temp data to compensate the
> clock rate.

Here is an interesting test of temperature compensation on the
BeagleBone Black where the frequency stability improved almost by a
factor of 20.

http://blog.dan.drown.org/beaglebone-black-ntpgps-server-temperature-compensation/

See also the following post, apparently the BBB can use a separate HW
timer to timestamp PPS, reducing the error and jitter significantly.

http://blog.dan.drown.org/beaglebone-black-timer-capture-driver/

It looks like this could be a really nice and cheap NTP/PTP server.

-- 
Miroslav Lichvar


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