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Re: Decreasing number of used satellites

From: Gary E. Miller
Subject: Re: Decreasing number of used satellites
Date: Tue, 14 Jun 2022 14:43:55 -0700

Yo Ulrich!

On Tue, 14 Jun 2022 11:14:35 +0000
"Wielant, Ulrich" <> wrote:

> Gpsd version: 3.23.1 (I am using the opensuse 15.2 gpsd package)

You realize that is not from us?  We can't support OpenSUSE.

> GPS: Garmin 24xd HVS

My condolences.  Pretty well unsupported by Garmin.

> Firmware: unknown - I cannot find any hint about the firmware version

You should see that in the (non-existent) manual.  You also might see
that in the NMEA on startup.

> NMEA version: don't know - have to ask Garmin but that takes time. I
> guess it's < 4.11.

They may not even know.  All their good people left over a decade ago.

> I managed to configure the GPS so that only GPS satellites are used
> and no other systems like GLONASS, QZSS etc.

Not a good idea.

> So all GSA and GSV
> messages should only report GPS PRNs.

If you want to cripple your device, we cant stop you.

> After I start gpsd most of the time all satellites are tagged with
> used=false in the SKY sentence. But in rare cases after I start gpsd
> they are tagged with used=true.

Once again, you have still not provided NMEA for us to look at.  A
description of your skyview would also help.

> I have created gpsd debugs for both cases start gpsd with the
> following parameters: /usr/sbin/gpsd -G -n -D 5 -N /dev/ttyS0 I have
> compared the debugs but I do not find the point why gpsd behaves
> different.

We did not ask for those.  Once again, without the NMEA, they are not
useful to us.  When we have your NMEA we can make out own logs.  But
we can't make NMEA from the logs.

> The only difference I can find is that DOP is set in the mask when
> satellites are reported as used.

When you ask us for help, it is because you are not finding the answers
you want.  For us to help, we need the raw NMEA.

> The GSA messages looks good to me. I
> only wonder that PRN 26 is sometimes reported twice. But that happens
> in both cases.

Firmware bug, report to Garmin.  Then get a good GNSS receiver from another

> used=true:   gpsd:IO: <= GPS:
> $GPGSA,A,3,05,16,18,23,26,26,27,,,,,,0.90,0.55,0.72*01 used=false:
> gpsd:IO: <= GPS: $GPGSA,A,3,05,16,18,23,26,27,,,,,,,0.90,0.55,0.72*05

Not what we asked for, or can use.

> Do you see what makes the difference between gpsd reporting
> satellites as used and not as used?

Nope.  Without the raw NMEA, nothing we can see.

Here is how to grab the NMEA:  "gpspipe -R -x 30 > raw.nmea"

Mail us the "raw.nmea" file.

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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