Skip to content
Switch branches/tags

Latest commit


Git stats


Failed to load latest commit information.
Latest commit message
Commit time

FDX reader for Garmin GND10

This is software to read the FDX protocol data seen on the USB port of Garmin GND10 gateways.

The GND10 unit is used on boats and translates between Nexus FDX and NMEA2000.


fdxread is available from and should be installed using pip:

$ pip install fdxread
$ fdxread --help  # Should be in $PATH

Tested on Linux and OS X, with Python 2.7 and Python 3.6. Goal is that it should work laptops and on any raspberry pis out there.

Note that on Debian systems you need to run apt-get install python-dev first for the LatLon23 (dependency) module to install/compile correctly. (at least on my armhf jessie system)

If you don't want to install it globally on the system, you can use a virtualenv like described in the development section below.

Running it

fdxread will read FDX either from a saved file (.dump/.nxb) or from a serial port.

It will send output to the terminal (stdout) on the format configured, normally NMEA0183.

$ fdxread /dev/ttyACM0
[ .. output cut .. ]

fdxread does not require root permissions. It should not be run under sudo. For access to devices in /dev/ the user it runs as should be added to the dialout group. (on Debian/Ubuntu)

There may be parse warnings logged to stderr that clutter the screen. These can be filtered with console redirection as usual: 2>/dev/null

When reading a saved file it is recommended to add "--pace 5" to slow down the output flow. A file for testing can be found in the source repository:

$ fdxread --pace 5 onsdagsregatta-2016-08-24.dump | head -10
WARNING:root:No handler for 6 byte 0x020200: 020200000081

Using it with OpenCPN and other software

For now the best way of running it is to pipe the output to a NMEA multiplexer using TCP.

I prefer the kplex multiplexer. After installing it, it can be started with: kplex tcp:direction=both,mode=server,address=,port=10110

You then pipe the output from fdxread into it using netcat: fdxread /dev/ttyACM0 | nc localhost 10110

Some information on how to set up OpenCPN and the Chrome application NMEA Sleuth can be found in .

--help output

usage: fdxread [-h] [--format fmt] [--seek n] [--pace n] [--send-psilfdx] [-v]

fdxread v0.9.1 - Nexus FDX parser (incl. Garmin GND10)

positional arguments:
  inputfile       Serial port or file to read from. Examples: /dev/ttyACM0,
                  COM3, ./file.dump

optional arguments:
  -h, --help      show this help message and exit
  --format fmt    Output mode, default nmea0183. (json, signalk, nmea0183,
                  none, raw)
  --seek n        Seek this many bytes into file before starting (for files)
  --pace n        Pace reading to n messages per second (for files)
  --send-psilfdx  Send initial mode change command to port (for NX2 server)
  -v, --verbose   Verbose output

fdxread is used to read FDX protocol data from Garmin GND10 units.

Background information

Everything here is deduced from staring at the arriving bytes while disconnecting some units and motoring in circles. Something was pretty simple to figure out, some other metrics I'm still not sure is right.

Use at your own risk.

On a side note, I believe this is the only open/freely available document on the format of the FDX protocol.


The development happens in git on

    $ git clone
    $ cd fdxread
    $ virtualenv --system-site-packages venv
    $ . venv/bin/activate
    $ pip install -r requirements.txt


The contents of this repository is licensed under GNU GPLv2. See the LICENSE file for more information.

Copyright (C) 2016-2017 Lasse Karstensen


Nexus FDX decoder for Garmin GND10




No packages published