NAME¶

gpsmon - real-time GPS packet monitor and control utility

SYNOPSIS¶

gpsmon [OPTIONS} [server[:port[:device]]]

gpsmon -h

gpsmon -V

DESCRIPTION¶

gpsmon is a monitor that watches packets coming from a GPS and displays them along with diagnostic information. It supports commands that can be used to tweak GPS settings in various ways; some are device-independent, some vary with the GPS chipset type. It will behave sanely, just dumping packets, when connected to a GPS type it knows nothing about.

gpsmon differs from a navigation client in that it mostly dumps raw data from the GPS, with only enough data-massaging to allow checks against expected output. It does not use gpsd to decode packets. There are many raw data types that gpsd knows about that gpsmon does not. In particular, this tool does not do any interpolation or modeling to derive climb/sink or error estimates. Nor does it discard altitude reports when the fix quality is too low.

The casual gpsd user will be better served by the cgps clients which display navigation data the same way for all GNSS receivers that gpsd supports. Such as cgps and xgps.

Unlike gpsd, gpsmon never writes control or probe strings to the device unless you explicitly tell it to. Thus, while it will auto-sync to binary packet types, it won’t automatically recognize a device shipping an extended NMEA protocol as anything other than a plain NMEA device. Use the -t option or the t to work around this.

gpsmon is a designed to run in a terminal emulator with a minimum 25x80 size; the non-GUI interface is a design choice made to accommodate users operating in constrained environments and over telnet or ssh connections. If run in a larger window, the size of the packet-log window will be increased to fit.

After startup (without -a or --nocurses), the top part of the screen reports the contents of several especially interesting packet types. The "PPS" field, if nonempty, is the delta between the last 1PPS top of second and the system clock at that time.

The bottom half of the screen is a scrolling hex dump of all packets the GPS is issuing. If the packet type is textual, any trailing CR/LF is omitted. Dump lines beginning ">>>" represent control packets sent to the GPS. Lines consisting of "PPS" surrounded by dashes, if present, indicate 1PPS and the start of the reporting cycle.

Unlike gpsd, gpsmon when run in direct mode does not do its own device probing. Thus, in particular, if you point it at a GPS with a native binary mode that happens to be emitting NMEA, it won’t identify the actual type unless the device emits a recognizable NMEA trigger sentence. The -t, --type option may help you.

gpsmon does not require root privileges, except maybe to access the serial port in direct mode. It will run fine as root.

OPTIONS¶

-?, -h, --help

-a, --nocurses

-d LVL, --debug LVL

-l FILE, --logfile FILE

-L, --list

-n, --nmea

-t TYPE, --type TYPE

ARGUMENTS¶

This program may be run in either of two modes, as a client for the gpsd daemon (and its associated control socket) or directly connected to a specified serial device.

By default, clients collect data from the local gpsd daemon running on localhost, using the default GPSD port 2947. The optional argument to any client may override this behavior: [server[:port[:device]]]

For further explanation, and examples, see the ARGUMENTS section in the gps(1) man page

If instead the argument contains slashes but no colons will it be treated as a serial device for direct connection. In direct-connect mode gpsmon will hunt for a correct baud rate and lock on to it automatically.

COMMANDS¶

The following device-independent commands are available while gpsmon is running:

i

Note that enabling probing might flip the device into another mode; in particular, it will flip a SiRF chip into binary mode as if you had used the "n" command. This is due to a limitation in the SiRF firmware that we can’t fix.

This command will generally do nothing after the first time you use it, because the device type will already have been discovered.

c

l

n

After you switch a dual-protocol GPS to NMEA mode with this command, it retains the information about the original type and its control capabilities. That is why the device type listed before the prompt doesn’t change.

q

s

t

x

X

Ctrl-S

Ctrl-Q

BUGS AND LIMITATIONS¶

The PPS Offset field will never be updated when running in client mode, even if you can see PPS events in the packet window. This limitation may be fixed in a future release.

RETURN VALUES¶

0

1

SEE ALSO¶

gpsd(8), cgps, (1)gpsctl(1), gps(1), *xgps(1)

RESOURCES¶

Project web site: <https://gpsd.io/>

COPYING¶

This file is Copyright 2013 by the GPSD project
SPDX-License-Identifier: BSD-2-clause

AUTHOR¶

Eric S. Raymond