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This file is Copyright 2009 by the GPSD project
SPDX-License-Identifier: BSD-2-clause
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   "-//OASIS//DTD DocBook XML V4.1.2//EN"
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<refentry id='gpsmon.1'>
<refentryinfo><date>30 March 2020</date></refentryinfo>
<refmeta>
<refentrytitle>gpsmon</refentrytitle>
<manvolnum>1</manvolnum>
<refmiscinfo class="source">The GPSD Project</refmiscinfo>
<refmiscinfo class="manual">GPSD Documentation</refmiscinfo>
</refmeta>
<refnamediv id='name'>
<refname>gpsmon</refname>
<refpurpose>real-time GPS packet monitor and control utility</refpurpose>
</refnamediv>
<refsynopsisdiv id='synopsis'>

<cmdsynopsis>
  <command>gpsmon</command>
      <arg choice='opt'>-L </arg>
      <arg choice='opt'>-V </arg>
      <arg choice='opt'>-h </arg>
      <arg choice='opt'>-n </arg>
      <arg choice='opt'>-a </arg>
      <arg choice='opt'>-l <replaceable>logfile</replaceable></arg>
      <arg choice='opt'>-t <replaceable>driver-prefix</replaceable></arg>
      <arg choice='opt'>
        <group>
          <arg choice='plain'>
            <replaceable>server</replaceable>
            <group>
              <replaceable>:port</replaceable>
              <group><replaceable>:device</replaceable></group>
            </group>
          </arg>
          <arg choice='plain'><replaceable>device</replaceable></arg>
        </group>
      </arg>
      <arg choice='opt'>-D <replaceable>debuglevel</replaceable></arg>
</cmdsynopsis>
</refsynopsisdiv>

<refsect1 id='description'><title>DESCRIPTION</title>

<para><application>gpsmon</application> 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.</para>

<para><application>gpsmon</application> 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.  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.</para>

<para>Unlike <application>gpsd</application>,
<application>gpsmon</application> 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 <option>-t</option> option or
the <command>t</command> to work around this.</para>

<para><application>gpsmon</application> 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.</para>

<para><application>gpsmon</application> accepts an -h option that
displays a usage message, or a -V option to dump the package
version and exit.</para>

<para>This program may be run in either of two modes, as a client for
the <application>gpsd</application> daemon (and its associated control
socket) or directly connected to a specified serial device.  When run
with no argument, it attempts to connect to the daemon.  If the
argument begins with a server:port specification it will also attempt
to connect to the daemon.  If the argument looks like a bare server
name it will attempt to connect to a daemon running on the default
gpsd port on that server.  Only if the device argument contains
slashes but no colons will it be treated as a serial device for direct
connection. In direct-connect mode <application>gpsmon</application>
will hunt for a correct baud rate and lock on to it
automatically. Possible cases look like this:</para>

<variablelist>
<varlistentry>
<term>localhost:/dev/ttyS1</term>
<listitem><para>Look at the default port of localhost, trying both
IPv4 and IPv6 and watching output from serial device 1.</para></listitem>
</varlistentry>
<varlistentry>
<term>example.com:2317</term>
<listitem><para>Look at port 2317 on example.com, trying both
IPv4 and IPv6.</para></listitem>
</varlistentry>
<varlistentry>
<term>71.162.241.5:2317:/dev/ttyS3</term>
<listitem><para>Look at port 2317 at the specified IPv4
address, collecting data from attached serial device 3.</para></listitem>
</varlistentry>
<varlistentry>
<term>[FEDC:BA98:7654:3210:FEDC:BA98:7654:3210]:2317:/dev/ttyS5</term>
<listitem><para>Look at port 2317 at the specified IPv6
address, collecting data from attached serial device 5.</para></listitem>
</varlistentry>
</variablelist>

<para>Unlike <application>gpsd</application>,
<application>gpsmon</application> 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 and -i options may help you.</para>

<para>The -F option is only valid in client mode; it specifies a
control socket to which the program should send device control
strings.  You must specify a valid pathname of a Unix-domain socket on
your local filesystem.</para>

<para>The -D option enables packet-getter debugging output and is
probably only useful to developers of the GPSD code.  Consult the
packet-getter source code for relevant values.</para>

<para>The -L option lists a table showing which GPS device types
<application>gpsmon</application> 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.</para>

<para>The -l option sets up logging to a specified 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.</para>

<para>The -n option forces gpsmon to request NMEA0183 packets instead of the
raw data stream from gpsd.</para>

<para>The -t option sets up a fallback 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.</para>

<para>The -a option 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.</para>

<para>After startup (without -a), 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.</para>

<para>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 &gt;&gt;&gt; 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.</para>

</refsect1>
<refsect1 id='commands'><title>COMMANDS</title>

<para>The following device-independent commands are available while
<application>gpsmon</application> is running:</para>

<variablelist>

<varlistentry>
<term>i</term>
<listitem>
<para>(Direct mode only.) Enable/disable subtype probing and
reinitialize the driver. In normal operation,
<application>gpsmon</application> 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 <application>gpsd</application> 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.</para>

<para>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 <quote>n</quote> command.  This is due to a
limitation in the SiRF firmware that we can't fix.</para>

<para>This command will generally do nothing after the first time you
use it, because the device type will already have been discovered.</para>
</listitem>
</varlistentry>

<varlistentry>
<term>c</term>
<listitem>
<para>(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.</para>
</listitem>
</varlistentry>

<varlistentry>
<term>l</term>
<listitem>
<para>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.</para>
</listitem>
</varlistentry>

<varlistentry>
<term>n</term>
<listitem>
<para>(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.</para>

<para>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.</para>
</listitem>
</varlistentry>

<varlistentry>
<term>q</term>
<listitem>
<para>Quit <application>gpsmon</application>.  Control-C, or whatever
your current interrupt character is, works as well.</para>
</listitem>
</varlistentry>

<varlistentry>
<term>s</term>
<listitem>
<para>(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.</para>

<para>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.</para>
</listitem>
</varlistentry>

<varlistentry>
<term>t</term>
<listitem>
<para>(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
<application>gpsmon</application> support;
<application>gpsmon</application> 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 <application>gpsmon</application>.</para>
</listitem>
</varlistentry>

<varlistentry>
<term>x</term>
<listitem>
<para>(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 <option>-x</option> of
<citerefentry><refentrytitle>gpsctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para>
</listitem>
</varlistentry>

<varlistentry>
<term>X</term>
<listitem>
<para>(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.</para>
</listitem>
</varlistentry>

<varlistentry>
<term>Ctrl-S</term>
<listitem>
<para>Freeze display, suspend scrolling in debug window.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Ctrl-Q</term>
<listitem>
<para>Unfreeze display, resume normal operation.</para>
</listitem>
</varlistentry>
</variablelist>

<refsect2><title>NMEA support</title>

<para>(These remarks apply to not just generic NMEA devices
but all extended NMEA devices for which
<application>gpsmon</application> presently has support.)</para>

<para>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.</para>

<para>There are no device-specific commands. Which generic
commands are available may vary by type: examine the output
of <command>gpsmon -l</command> to learn more.</para>
</refsect2>

<refsect2><title>SiRF support</title>
<para>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.</para>

<para>The following commands are supported for SiRF GPSes only:</para>

<variablelist>
<varlistentry>
<term>A</term>
<listitem>
<para>(Direct mode only.) Toggle reporting of 50BPS subframe data.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>M</term>
<listitem>
<para>(Direct mode only.) Set (M1) or clear (M0) static
navigation. The SiRF documentation says <quote>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.</quote></para>

<para>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.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>P</term>
<listitem>
<para>(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.</para>
</listitem>
</varlistentry>
</variablelist>

<para>To interpret what you see, you will need a copy of the
<citetitle>SiRF Binary Protocol Reference Manual</citetitle>.</para>

</refsect2>
<refsect2><title>u-blox support</title>
<para>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.</para>

</refsect2>
</refsect1>
<refsect1 id='bugs'><title>BUGS AND LIMITATIONS</title>

<para>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.</para>

<!--
Debug window dumps of control message sends to the GPS (preceded
by '>>>') are only supported for the following drivers: NMEA, SiRF,
EverMore, Navcom, UBX, TSIP, iTalk, Garmintxt. This feature will not
work for Zodiacs and not always work for Garmins in binary
mode.
-->

</refsect1>
<refsect1 id='see_also'><title>SEE ALSO</title>
<para>
<citerefentry><refentrytitle>gpsd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>gpsdctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>gps</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>libgps</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>libgpsmm</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>gpsprof</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>gpsfake</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>gpsctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>gpscat</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
<citerefentry><refentrytitle>gpspipe</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
</para>
</refsect1>

<refsect1 id='maintainer'><title>AUTHOR</title>

<para>Eric S. Raymond <email>esr@thyrsus.com</email>.</para>
</refsect1>

</refentry>

