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

From: Miroslav Lichvar
Subject: Re: [gpsd-users] Garmin 18X-5Hz
Date: Mon, 15 Aug 2016 13:55:53 +0200
User-agent: Mutt/1.6.2 (2016-07-01)

On Fri, Aug 12, 2016 at 11:29:48AM -0700, Gary E. Miller wrote:
> On Fri, 12 Aug 2016 11:52:34 +0200
> Miroslav Lichvar <address@hidden> wrote:
> > As ntpd reads SHM only once per second,
> No.  Minimmum read on an unpatched ntpd is 8 seconds.  See minpoll.  I
> prefer to have it at 16 or 32 for better stability.

The minpoll and maxpoll options control how often ntpd polls the
refclock driver, not how often the driver polls its source. The SHM
driver reads the SHM segment once per second. E.g. if minpoll and
maxpoll are 3, there will be 8 samples collected and filtered between
clock updates. If you increase the polling interval, more samples will
be collected between updates and that can improve the stability of the
filtered offset.

Miroslav Lichvar

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