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Re: Glitching GPS feed
From: |
Mike Tubby G8TIC |
Subject: |
Re: Glitching GPS feed |
Date: |
Wed, 18 Oct 2023 18:58:48 +0100 |
User-agent: |
Mozilla Thunderbird |
Nick,
Firstly, I rarely use NMEA GPS - I prefer uBlox binary mode, but my
observations:
* I am used to seeing $GPGGA and/or $GPRMC fixes from GPS
* you have $GNRMC and $GNGGA messages which are the newer GNSS agnostic
messages
* there does appear to be two levels of connection - shown in your data:
gpsd://10.253.154.161:2947#tcp://10.253.132.170:7000
* you PDOP is 1.04 and you're seeing enough satellites for a fix
* GPSD appears to be parsing and decoding your location:
"lat":57.314202167,"lon":-111.764077667,"alt":223.400
which puts you in Fort McKay, Canada, here:
https://www.google.com/maps/@57.186758,-111.6367851,3a,75y,90t/data=!3m8!1e2!3m6!1sAF1QipNCGXldgZQf-2D2rP2XGO_pnMIYE6ngcnkat85w!2e10!3e12!6shttps:%2F%2Flh5.googleusercontent.com%2Fp%2FAF1QipNCGXldgZQf-2D2rP2XGO_pnMIYE6ngcnkat85w%3Dw114-h86-k-no!7i4608!8i3456?entry=ttu
* The $GNTXT messages appear to be an indication that it's transmit
buffer is overflowing - it may be configured to generate messages faster
than it's serial port can deliver them to the host and is dropping
frames, or may be being delivered over busiy I2C or SPI bus - depending
on the architecture of the device with the GNSS.
There is plenty of discussion of this issue on the interweb if you
search for "$GNTXT,01,01,00,txbuf alloc*61" and some suggestions that it
is common place on some of the Chinese knock-off uBlox replicas.
Mike
On 18/10/2023 09:55, Nick Taylor wrote:
Hi all
After some advice...
We have a customer who is providing us with a feed via their gpsd
daemon - we don't have exact details of how they are doing this behind
the scenes but it sounds like there are a couple of devices in between
us and the actual GPS receiver.
We can pickup feed using gpsd:// source, however when using this feed
cgps seems to glitch, keeps resetting and never seems to get a fix.
I'm attaching dumps of the received feed (one is gpspipe -r and the
other gpspipe -R). These show feed seems to contain multiple GNTXT
messages which may or may not be causing the issue.
Any suggestions would be much appreciated.
Thanks and regards
Nick