gpsmon(1) GPSD Documentation gpsmon(1)
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
Print a usage message and exit.
-a, --nocurses
Enables a special debugging mode that does not use screen painting.
Packets are dumped normally, any character typed suspends packet
dumping and brings up a command prompt. This feature will mainly be
of interest to GPSD developers.
-d LVL, --debug LVL
Enable packet-getter debugging output and is probably only useful to
developers of the GPSD code. Consult the packet-getter source code
for relevant values.
-l FILE, --logfile FILE
Set up logging to a specified file (FILE) to start immediately on
device open. This may be useful is, for example, you want to capture
the startup message from a device that displays firmware version
information there.
-L, --list
Lists a table showing which GPS device types this gpsmon has built-in
support for, and which generic commands can be applied to which GPS
types, and then exits. Note that this does not list type-specific
commands associated with individual GPS types.
-n, --nmea
Force gpsmon to request NMEA0183 packets instead of the raw data
stream from gpsd.
-t TYPE, --type TYPE
Set a fallback type (TYPE). Give it a string that is a distinguishing
prefix of exactly one driver type name; this will be used for mode,
speed, and rate switching if the driver selected by the packet type
lacks those capabilities. Most useful when the packet type is NMEA
but the device is known to have a binary mode, such as SiRF binary.
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
(Direct mode only.) Enable/disable subtype probing and reinitialize
the driver. In normal operation, gpsmon does not send configuration
strings to the device (except for wakeup strings needed to get it to
send data, if any). The command 'i1' causes it to send the same
sequence of subtype probes that gpsd would. The command 'i0' turns
off probing; 'i' alone toggles the bit. In either case, the current
driver is re-selected; if the probe bit is enabled, probes will begin
to be issued immediately.
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
(Direct mode only.) Change cycle time. Follow it with a number
interpreted as a cycle time in seconds. Most devices have a fixed
cycle time of 1 second, so this command may fail with a message.
l
Toggle packet logging. If packet logging is on, it will be turned off
and the log closed. If it is off, logging to the filename following
the l will be enabled. Differs from simply capturing the data from
the GPS device in that only whole packets are logged. The logfile is
opened for append, so you can log more than one portion of the packet
stream and they will be stitched together correctly.
n
(Direct mode only.) With an argument of 0, switch device to NMEA mode
at current speed; with an argument of 1, change to binary (native)
mode. With no argument, toggle the setting. Will show an error if the
device doesn't have such modes.
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
Quit gpsmon. Control-C, or whatever your current interrupt character
is, works as well.
s
(Direct mode only.) Change baud rate. Follow it with a number
interpreted as bits per second, for example "s9600". The speed number
may optionally be followed by a colon and a
wordlength-parity-stopbits specification in the traditional style,
e.g 8N1 (the default), 7E1, etc. Some devices don't support serial
modes other than their default, so this command may fail with a
message.
Note
Use this command with caution. On USB and Bluetooth GPSs it is also
possible for serial mode setting to fail either because the serial
adaptor chip does not support non-8N1 modes or because the device
firmware does not properly synchronize the serial adaptor chip with
the UART on the GPS chipset when the speed changes. These failures
can hang your device, possibly requiring a GPS power cycle or (in
extreme cases) physically disconnecting the NVRAM backup battery.
t
(Direct mode only.) Force a switch of monitoring type. Follow it with
a string that is unique to the name of a gpsd driver with gpsmon
support; gpsmon will switch to using that driver and display code.
Will show an error message if there is no matching gpsd driver, or
multiple matches, or the unique match has no display support in
gpsmon.
x
(Direct mode only.) Send hex payload to device. Following the command
letter you may type hex digit pairs; end with a newline. These will
become the payload of a control packet shipped to the device. The
packet will be wrapped with headers, trailers, and checksum
appropriate for the current driver type. The first one or two bytes
of the payload may be specially interpreted, see the description of
the -x of gpsctl 1 .
X
(Direct mode only.) Send raw hex bytes to device. Following the
command letter you may type hex digit pairs; end with a newline.
These will be shipped to the device.
Ctrl-S
Freeze display, suspend scrolling in debug window.
Ctrl-Q
Unfreeze display, resume normal operation.
NMEA support
(These remarks apply to not just generic NMEA devices but all extended
NMEA devices for which gpsmon presently has support.)
All fields are raw data from the GPS except (a) the "Cooked PVT" window
near top of screen, provided as a check and (b) the "PPS offset" field.
There are no device-specific commands. Which generic commands are
available may vary by type: examine the output of gpsmon -l to learn
more.
SiRF support
Most information is raw from the GPS. Underlined fields are derived by
translation from ECEF coordinates or application of leap-second and local
time-zone offsets. 1PPS is the clock lag as usual.
The following commands are supported for SiRF GPSes only:
A
(Direct mode only.) Toggle reporting of 50BPS subframe data.
M
(Direct mode only.) Set (M1) or clear (M0) static navigation. The
SiRF documentation says "Static navigation is a position filter
designed to be used with motor vehicles. When the vehicle's velocity
falls below a threshold, the position and heading are frozen, and
velocity is set to zero. This condition will continue until the
computed velocity rises above 1.2 times the threshold or until the
computed position is at least a set distance from the frozen place.
The threshold velocity and set distance may vary with software
versions."
Non-static mode is designed for use with road navigation software, which
often snaps the reported position to the nearest road within some
uncertainty radius. You probably want to turn static navigation off for
pedestrian use, as it is likely to report speed zero and position
changing in large jumps.
P
(Direct mode only.) Toggle navigation-parameter display mode. Toggles
between normal display and one that shows selected navigation
parameters from MID 19, including the Static Navigation bit toggled
by the 'M' command.
To interpret what you see, you will need a copy of the SiRF Binary
Protocol Reference Manual.
u-blox support
Most information is raw from the GPS. Underlined fields are derived by
translation from ECEF coordinates. 1PPS is the clock lag as usual. There
are no per-type special commands.
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
on success.
1
on failure
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
GPSD, Version 3.24 2022-04-27 gpsmon(1)
mgpsd 3.24 - Generated Sun Jan 1 10:34:56 CST 2023