emmanuelguegan / gpsdate

Simple tool for fetching date and time from a GPS receiver and saving it as a local time.

gpsdate

Gpsdate is a simple tool which reads date and time from a GPS receiver connected via serial port (or a CDC ACM virtual serial port over USB) and saves it as a local time on Linux.

The program waits for a specified maximum time until a valid $GPRMC NMEA sentence is received. If the GPS receiver is not fixed and no valid time information is received, the local time remains unchanged.

This version is a fork from https://github.com/adamheinrich/gpsdate attended to correct week rollover GPS issue.

See : https://en.wikipedia.org/wiki/GPS_week_number_rollover

Building

git clone https://github.com/emmanuelguegan/gpsdate # Or download as zip
cd gpsdate
make

Usage

Connect the GPS receiver and obtain ts device name. Mine is /dev/ttyACM0 as found in dmesg:

$ dmesg | tail
...
[22625.034377] usb 1-1.1: new full-speed USB device number 9 using ehci_hcd
[22625.128637] cdc_acm 1-1.1:1.0: ttyACM0: USB ACM device

Then check if it sends back NMEA sentences, e.g. using cat:

$ stty -F /dev/ttyACM0 9600 # Optional
$ cat /dev/ttyACM0
$GPRMC,191745.80,V,,,,,,,160314,,,N*7B
$GPVTG,,,,,,,,,N*30

Now you can gpsdate to change local time:

# ./gpsdate /dev/ttyACM0
Local time was: 2022-02-15 16:55:45 (GMT)
GPS   time  is: 2022-02-15 16:55:45 (GMT)
Adjtime : Successfully updated local time.

Note that changing time requires root privileges. To achieve this, run:

sudo ./gpsdate /dev/ttyACM0

It is possible to change the default baud rate or a timeout. Run the program with option -h for a complete list of options:

$ ./gpsdate -h
Usage: ./gpsdate [options] port
Sets time from a GPS receiver connected to a serial port as a local time.

Options:
  -b <baudrate>    Sets baud rate. Only a limited set of baud rates {2400,
                   4800, ..., 230400} is supported (Default 9600 baud).
  -t,-d <timeout>  Sets the maximum timeout in seconds or 0 for no timeout
                   (Default 10 seconds)
  -h               Displays this help.
  -r               Correct GPS week number rollover
  -n               Dry run , Get the GPS time but don't apply it

License

Gpsdate is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

See COPYING for details.