GPS Time

Set the system time by reading from a GPS device connected via serial/USB.

This code opens a serial device at a specified baud rate, then trawls through the data received looking for a $GPRMC message from the GPS. This particular message includes not just the time but also the date. A sample message might be:

$GPRMC,211321.000,A,5309.7743,N,01204.5576,W,0.17,78.41,200813,,,A*4E

The second field has the time in the form HHMMSS.NNN where N is the time in milliseconds. The tenth field has the date in the form YYMMDD in a not particularly Y2K-friendly format.

Compiling and Installing

The application doesn’t require any third-party libraries apart from libc. You’ll need a C compiler such as gcc or clang, make, and libc. Compiling should just be a matter of typing make. If you get compiler errors or warnings, raise a bug or get in touch.

You can install the binary wherever you see fit, but /usr/local/bin is a reasonable option.

Usage

The program takes three optional arguments:

• -s BAUD (sets the baud rate)
• -l DEVICE (sets the serial device)
• -v (prints verbose debugging info)

A good example might be:

$ gps_time -s 9600 -l /dev/ttyu1 -v