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Re: [gpsd-users] Garmin 18X-5Hz

From: Gary E. Miller
Subject: Re: [gpsd-users] Garmin 18X-5Hz
Date: Fri, 12 Aug 2016 11:37:22 -0700

Yo Miroslav!

On Fri, 12 Aug 2016 10:52:02 +0200
Miroslav Lichvar <address@hidden> wrote:

> On Thu, Aug 11, 2016 at 12:19:46PM -0700, Gary E. Miller wrote:
> > OTOH, ntpd will not accept time corrections faster than every 8
> > seconds without a patch.  I find that every every 16 or 32 seconds
> > gives better results.  Even longer may be even better, depending on
> > local clock stability.  
> Yes, the stability of the clock is the most important factor here. If
> the machine is just sitting idle all day, longer update intervals may
> work better, but when the temperature starts changing rapidly due to
> CPU or other components with variable power consumption, even 8 second
> update interval may be too long to keep the kernel PLL locked. In such
> case giving ntpd more samples by increasing the PPS rate would be
> pointless.

Not my experience.  And not possible without patching your ntpd.

NTP visualization tools have been making rapid progress this summer.  The
next ntpsec release, coming soon, will include 'ntpviz'.  Early users
are confirming or disproving, many old-wives-tales about NTP.

On thing that is coming to light, ntpd tends to chase quantization errors
rather than averge them out.  No solutions yet.

For exammple:

You'll notice I'm also graphing temps, at the bottom.

I would encourage you to setup some graphs and prove your point.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

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