Re: Multiple TPV lines per sec?

[Gary E. Miller]

Yo Tor!

On Tue, 8 Jun 2021 16:19:37 +0200
Tor Rune Skoglund <trs@fourc.eu> wrote:

> Thanks Gary, for the hints below. We tried using -b, -p and both but
> to no avail, so we ended up with delaying starting gpsd until we are
> sure that the modem setup has stablized.

Ouch.  But not unexpected with a GNSS modem.

> However, we just recently noticed that the issue also appear after 
> having driven through a tunnel:

Without IMU support, tunnels, and urban canyons, are problems.

> After startup, a TPV comes every second as expected, for example like
> this:

Maybe you expected that, but often not the case.

> Then, the vehicle enters a tunnel, TPV messages comes like this once
> a second while in the tunnel (as expected):

Maybe you expected that, but often not the case.

> Then the vehicle leaves the tunnel; two TPVs start coming every
> second quite, e.g. like this:

Pretty common.  Note that the 2nd one contained more information than
the first one.  As the data dribbles in to gpsd, gpsd pused it out as JSON.

> As one can see, the messages that come simultaneous are quite equal,
> but "track" and "magtrack" are missing in the first one.

Can 't be equal when they are different.

> Restarting
> gpsd resets the TPV reporting back to the initial one with one line
> every second.

This is because of your receiver firmware changing its output due to
changing conditions.  Nothing can be done about it.  All GNSS receivers
do it.

> I was thinking there might be a config option for the GNSS device or 
> something that could cause this, but have no immediate clues so any
> help and pointers would be appreciated.

u-blox 9 has over a thousand distinct configuration options.  Feel
free to spend your next year, or two, exploring how they all interact.

Or, live with it.  It is perfectly normal and expected.

> The GNSS in question is the one on a Sierra Wireless MC7304 modem but
> we also see on e.g. SimCom modems' GNSS.

Sadly, they doc is not acvailable for public download.  I do see a 
copyright date of 2015, and that it is EOL, so not a modern modem.

Without doc I can't say anything about your device.

RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
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