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Re: FreeBSD Garmin 18x LVC receiver - precision -20

From: Gary E. Miller
Subject: Re: FreeBSD Garmin 18x LVC receiver - precision -20
Date: Mon, 19 Oct 2020 11:09:07 -0700

Yo Philippe!

On Mon, 19 Oct 2020 14:57:27 +0200
"Philippe Maechler" <> wrote:

> Thank you for the answer. I didn’t knew that the prescision is a
> constant.

No one knows all this stuff.

> While googling I saw other outputs with a precision of -3
> and the like.

-3 is the assumed precision for time from the serial stream.

> So I tought it has something to do with “how accurate
> the position is”

Your thought is correct.  PPS is kinda sorta accurate to -20.

> Many of the tools that are mentioned on the gpsd howtos are not
> available on freebsd. So I only had the telnet output at hands. 

You have to complain to the FreeBSD maintainer about that.  I beleive they
are available, but as a separate package.

> Since I had the impression that the receiver is not “precise” I debug
> ntpd further😊

What do you think you need to debug?

> > Did you read the time howtos?   
> I mostly read howtos on gpsd, ntpd and installing the receiver and a
> huge chapter on PPS scaling (all from the gpsd website) is there any
> other how to I should have a look at? I’m currently re-reading the
> gpsd-time-service-howto

That is the right stuff to read.  Then ask questions here.

> server iburst maxpoll 9
> peer 

I guess you are using NTP Classic, not NTPsec.  With NTPsec a peer
and a server are the same thing.

> server mode 1 prefer
> fudge time1 0.000 refid PPS

That is configuring ntp direct to the serial port.  gpsd is not being
used by ntpd.  But if gpsd is connected to the receiver, then ntpd can
not also directly read the receiver.  This is not per the gpsd howto's as
it does not use gpsd!

> I’m currently in Home-Office and can’t put Hands on the GPS receiver.

That is why there is the internet.

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

            Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin

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