[ntp:questions] Tutorial for setting up Garmin 18 LVC on FreeBSD 8.0

ryandoyle rd at ryandoyle.net
Tue Feb 23 00:35:58 UTC 2010

On Feb 23, 5:13 am, unruh <un... at wormhole.physics.ubc.ca> wrote:
> On 2010-02-22, ryandoyle <r... at ryandoyle.net> wrote:
> > For anyone interested in setting up a Garmin 18 LVC GPS receiver on
> > FreeBSD 8, I wrote up a fairly detailed tutorial of my experiences
> > here:http://blog.doylenet.net/?p=145
> > A couple of months ago I thought it would be a neat idea to run a
> > strat 1 time server at my work. I hadn't had any experience with NTP
> > before, didn't know what local clock drivers were etc... and coming
> > from a Linux background I had very little experience with FreeBSD.
> I disagree with your comments re the accuracy on Linux. I have
> consistantly gotten 2usec accuracy on Linux with ntpd, (and with chrony, Lichvar
> gets sub usec accuracy with no change in the kernel).

Admittedly, the wild inaccuracies that I was experiencing could have
been due to my setup. I was running GPSd and using it as a local clock
driver for NTP. At the time is seemed the "cleanest" way. Also I found
that FreeBSD becomes stable at a much quicker rate compared to Linux.
I never like patching the Linux kernel when package management is very
tightly integrated into the distribution such as RHEL/CentOS which I
was using and is why I didn't try other methods such as those found
here: http://time.qnan.org/.

On Feb 23, 2:55 am, "David J Taylor" <david-tay... at blueyonder.delete-
this-bit.and-this-part.co.uk.invalid> wrote:

> Thanks for doing that, Ryan.  I've added a link from my own Web page:

>   http://www.satsignal.eu/ntp/FreeBSD-GPS-PPS.htm

> Cheers,
> David

Appreciated David, thanks for your write up as well, was a great help.

On 2010-02-22, Thomas Laus <lau... at acm.org> wrote:

> You should state this in your writeup.  Someone new to FreeBSD could be
> using your instructions as a cookbook recipe.  The deviations from the
> default and best practice defaults should have an explaination of the
> benefits and tradeoffs of doing something.

Tom, I appreciate your concern for security. I've changed the wording
a bit and justified why I have permitted them in my case.

On Feb 23, 4:20 am, Dave Hart <daveh... at gmail.com> wrote:

> Agreed.  FYI with 4.2.6 and later, "minpoll 4" on your refclock is all
> that's needed.  Maxpoll is essentially clamped to minpoll for
> refclocks.

> I'm not sure when this changed, but I believe it was after 4.2.4.

> Cheers,
> Dave Hart

Dave, thanks for the information, I'll update this for completeness.

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