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Re: GPSD doesn't report signal dropout

From: Gary E. Miller
Subject: Re: GPSD doesn't report signal dropout
Date: Tue, 6 Oct 2020 18:53:38 -0700

Yo Tom!

On Wed, 7 Oct 2020 14:24:23 +1300
Tom Isaacson <> wrote:

> We are using gpsd 3.19

gpsd 3.19 is a tad old.  3.20 fixes some bugs in 3.19.

Built from source or from a distro package?

> on a Quectel EC25 Mini PCIe
> ( GPS seems to work fine
> until we lose the signal (e.g. go into a tunnel).

I see no doc on what the part sends out.  Hard to support an undocumented

> The NMEA0183 output shows when I disconnect/reconnect the antenna:

I see no direct indication of antenna disconnect.  I don't think
NMEA understands the concpet.  AFAIK that requires a binary protocol.

> See $GPRMC validity ( change from A (ok)
> to V (invalid) and back again.

Which may be caused by antenna disconnect, or by other things.

> The GPSD log shows the same - you can see the lock disappear and
> reappear:

I don't see,it.  Way too short a data sample, at too low a -D level,
with no timestamps to line up with the libgps output.  Maybe more
obvious at -D5.

The timestamps on the nmea-disconnect.txt do not line up wit the timestamps
in gpsd-api-disconnect.txt so I can not coorelate them.

I do see a warning about bad time:

gpsd:WARN: merge_hhmmss(), malformed time

But without the matching input I don't know why.

I do see no TPV from 1:00:02 to 1:00:07

> But the client app never sees the dropout:

What client app?


20 seconds is a bit short.

whatI prefer is simultaineous capture if gpsd input and output.

In separate terminals, run:
        gpspipe -w > json.log
        gpspipe -R > raw.log

Send those files here.

> Any suggestions? Is this a known bug, have we just compiled with the
> wrong flags, what?

Not a known bug.  Since you showed nothing of how you compiled I can not
comment on that, but I doubt a build error.  Since you compiled it, try
3.20 or git head.

If you have doc on the protocol, send that too.  As aa general rule gpsd
can not support undocumented parts.

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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