1GPSMON(1) GPSD Documentation GPSMON(1)
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6 gpsmon - real-time GPS packet monitor and control utility
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9 gpsmon [-?] [--debug LVL] [--help] [--list] [--logfile FILE] [--nmea]
10 [--nocurses] [--type TYPE] [--version] [-a] [-D LVL] [-h] [-L]
11 [-l FILE] [-n] [-t TYPE] [-V]
12 [[ server [:port [:device]] | device ]]
13
15 gpsmon is a monitor that watches packets coming from a GPS and displays
16 them along with diagnostic information. It supports commands that can
17 be used to tweak GPS settings in various ways; some are
18 device-independent, some vary with the GPS chipset type. It will behave
19 sanely, just dumping packets, when connected to a GPS type it knows
20 nothing about.
21 gpsmon differs from a navigation client in that it mostly dumps raw
23 data from the GPS, with only enough data-massaging to allow checks
24 against expected output. In particular, this tool does not do any
25 interpolation or modeling to derive climb/sink or error estimates. Nor
26 does it discard altitude reports when the fix quality is too low.
27 Unlike gpsd, gpsmon never writes control or probe strings to the device
29 unless you explicitly tell it to. Thus, while it will auto-sync to
30 binary packet types, it won't automatically recognize a device shipping
31 an extended NMEA protocol as anything other than a plain NMEA device.
32 Use the -t option or the t to work around this.
33 gpsmon is a designed to run in a terminal emulator with a minimum 25x80
35 size; the non-GUI interface is a design choice made to accommodate
36 users operating in constrained environments and over telnet or ssh
37 connections. If run in a larger window, the size of the packet-log
38 window will be increased to fit.
39 This program may be run in either of two modes, as a client for the
41 gpsd daemon (and its associated control socket) or directly connected
42 to a specified serial device. When run with no argument, it attempts to
43 connect to the daemon. If the argument begins with a server:port
44 specification it will also attempt to connect to the daemon. If the
45 argument looks like a bare server name it will attempt to connect to a
46 daemon running on the default gpsd port on that server. Only if the
47 device argument contains slashes but no colons will it be treated as a
48 serial device for direct connection. In direct-connect mode gpsmon will
49 hunt for a correct baud rate and lock on to it automatically. Possible
50 cases look like this:
51 localhost:/dev/ttyS1
53 Look at the default port of localhost, trying both IPv4 and IPv6
54 and watching output from serial device 1.
55 example.com:2317
57 Look at port 2317 on example.com, trying both IPv4 and IPv6.
58 71.162.241.5:2317:/dev/ttyS3
60 Look at port 2317 at the specified IPv4 address, collecting data
61 from attached serial device 3.
62 [FEDC:BA98:7654:3210:FEDC:BA98:7654:3210]:2317:/dev/ttyS5
64 Look at port 2317 at the specified IPv6 address, collecting data
65 from attached serial device 5.
66 After startup (without -a, --nocurses), the top part of the screen
68 reports the contents of several especially interesting packet types.
69 The "PPS" field, if nonempty, is the delta between the last 1PPS top of
70 second and the system clock at that time.
71 The bottom half of the screen is a scrolling hex dump of all packets
73 the GPS is issuing. If the packet type is textual, any trailing CR/LF
74 is omitted. Dump lines beginning >>> represent control packets sent to
75 the GPS. Lines consisting of "PPS" surrounded by dashes, if present,
76 indicate 1PPS and the start of the reporting cycle.
77 Unlike gpsd, gpsmon run in direct mode does not do its own device
79 probing. Thus, in particular, if you point it at a GPS with a native
80 binary mode that happens to be emitting NMEA, it won't identify the
81 actual type unless the device emits a recognizable NMEA trigger
82 sentence. The -t, --type option may help you.
83
85 -?, -h, --help
86 Print a usage message and exit.
87 -a, --nocurses
89 Enables a special debugging mode that does not use screen painting.
90 Packets are dumped normally; any character typed suspends packet
91 dumping and brings up a command prompt. This feature will mainly be
92 of interest to GPSD developers.
93 -d LVL, --debug LVL
95 Enable packet-getter debugging output and is probably only useful
96 to developers of the GPSD code. Consult the packet-getter source
97 code for relevant values.
98 -l FILE, --logfile FILE
100 Set up logging to a specified file (FILE) to start immediately on
101 device open. This may be useful is, for example, you want to
102 capture the startup message from a device that displays firmware
103 version information there.
104 -L, --list
106 Lists a table showing which GPS device types this gpsmon has
107 built-in support for, and which generic commands can be applied to
108 which GPS types, and then exits. Note that this does not list
109 type-specific commands associated with individual GPS types.
110 -n, --nmea
112 Force gpsmon to request NMEA0183 packets instead of the raw data
113 stream from gpsd.
114 -t TYPE, --type TYPE
116 Set a fallback type (TYPE). Give it a string that is a
117 distinguishing prefix of exactly one driver type name; this will be
118 used for mode, speed, and rate switching if the driver selected by
119 the packet type lacks those capabilities. Most useful when the
120 packet type is NMEA but the device is known to have a binary mode,
121 such as SiRF binary.
122
124 The following device-independent commands are available while gpsmon is
125 running:
126 i
128 (Direct mode only.) Enable/disable subtype probing and reinitialize
129 the driver. In normal operation, gpsmon does not send configuration
130 strings to the device (except for wakeup strings needed to get it
131 to send data, if any). The command 'i1' causes it to send the same
132 sequence of subtype probes that gpsd would. The command 'i0' turns
133 off probing; 'i' alone toggles the bit. In either case, the current
134 driver is re-selected; if the probe bit is enabled, probes will
135 begin to be issued immediately.
136 Note that enabling probing might flip the device into another mode;
138 in particular, it will flip a SiRF chip into binary mode as if you
139 had used the “n” command. This is due to a limitation in the SiRF
140 firmware that we can't fix.
141 This command will generally do nothing after the first time you use
143 it, because the device type will already have been discovered.
144 c
146 (Direct mode only.) Change cycle time. Follow it with a number
147 interpreted as a cycle time in seconds. Most devices have a fixed
148 cycle time of 1 second, so this command may fail with a message.
149 l
151 Toggle packet logging. If packet logging is on, it will be turned
152 off and the log closed. If it is off, logging to the filename
153 following the l will be enabled. Differs from simply capturing the
154 data from the GPS device in that only whole packets are logged. The
155 logfile is opened for append, so you can log more than one portion
156 of the packet stream and they will be stitched together correctly.
157 n
159 (Direct mode only.) With an argument of 0, switch device to NMEA
160 mode at current speed; with an argument of 1, change to binary
161 (native) mode. With no argument, toggle the setting. Will show an
162 error if the device doesn't have such modes.
163 After you switch a dual-protocol GPS to NMEA mode with this
165 command, it retains the information about the original type and its
166 control capabilities. That is why the device type listed before the
167 prompt doesn't change.
168 q
170 Quit gpsmon. Control-C, or whatever your current interrupt
171 character is, works as well.
172 s
174 (Direct mode only.) Change baud rate. Follow it with a number
175 interpreted as bits per second, for example "s9600". The speed
176 number may optionally be followed by a colon and a
177 wordlength-parity-stopbits specification in the traditional style,
178 e.g 8N1 (the default), 7E1, etc. Some devices don't support serial
179 modes other than their default, so this command may fail with a
180 message.
181 Use this command with caution. On USB and Bluetooth GPSs it is also
183 possible for serial mode setting to fail either because the serial
184 adaptor chip does not support non-8N1 modes or because the device
185 firmware does not properly synchronize the serial adaptor chip with
186 the UART on the GPS chipset when the speed changes. These failures
187 can hang your device, possibly requiring a GPS power cycle or (in
188 extreme cases) physically disconnecting the NVRAM backup battery.
189 t
191 (Direct mode only.) Force a switch of monitoring type. Follow it
192 with a string that is unique to the name of a gpsd driver with
193 gpsmon support; gpsmon will switch to using that driver and display
194 code. Will show an error message if there is no matching gpsd
195 driver, or multiple matches, or the unique match has no display
196 support in gpsmon.
197 x
199 (Direct mode only.) Send hex payload to device. Following the
200 command letter you may type hex digit pairs; end with a newline.
201 These will become the payload of a control packet shipped to the
202 device. The packet will be wrapped with headers, trailers, and
203 checksum appropriate for the current driver type. The first one or
204 two bytes of the payload may be specially interpreted, see the
205 description of the -x of gpsctl(1).
206 X
208 (Direct mode only.) Send raw hex bytes to device. Following the
209 command letter you may type hex digit pairs; end with a newline.
210 These will be shipped to the device.
211 Ctrl-S
213 Freeze display, suspend scrolling in debug window.
214 Ctrl-Q
216 Unfreeze display, resume normal operation.
217 NMEA support
219 (These remarks apply to not just generic NMEA devices but all extended
220 NMEA devices for which gpsmon presently has support.)
221 All fields are raw data from the GPS except (a) the "Cooked PVT" window
223 near top of screen, provided as a check and (b) the "PPS offset" field.
224 There are no device-specific commands. Which generic commands are
226 available may vary by type: examine the output of gpsmon -l to learn
227 more.
228 SiRF support
230 Most information is raw from the GPS. Underlined fields are derived by
231 translation from ECEF coordinates or application of leap-second and
232 local time-zone offsets. 1PPS is the clock lag as usual.
233 The following commands are supported for SiRF GPSes only:
235 A
237 (Direct mode only.) Toggle reporting of 50BPS subframe data.
238 M
240 (Direct mode only.) Set (M1) or clear (M0) static navigation. The
241 SiRF documentation says “Static navigation is a position filter
242 designed to be used with motor vehicles. When the vehicle's
243 velocity falls below a threshold, the position and heading are
244 frozen, and velocity is set to zero. This condition will continue
245 until the computed velocity rises above 1.2 times the threshold or
246 until the computed position is at least a set distance from the
247 frozen place. The threshold velocity and set distance may vary with
248 software versions.”
249 Non-static mode is designed for use with road navigation software,
251 which often snaps the reported position to the nearest road within
252 some uncertainty radius. You probably want to turn static
253 navigation off for pedestrian use, as it is likely to report speed
254 zero and position changing in large jumps.
255 P
257 (Direct mode only.) Toggle navigation-parameter display mode.
258 Toggles between normal display and one that shows selected
259 navigation parameters from MID 19, including the Static Navigation
260 bit toggled by the 'M' command.
261 To interpret what you see, you will need a copy of the SiRF Binary
263 Protocol Reference Manual.
264 u-blox support
266 Most information is raw from the GPS. Underlined fields are derived by
267 translation from ECEF coordinates. 1PPS is the clock lag as usual.
268 There are no per-type special commands.
269
271 The PPS Offset field will never be updated when running in client mode,
272 even if you can see PPS events in the packet window. This limitation
273 may be fixed in a future release.
274
276 gpsd(8), gpsdctl(8), gps(1), libgps(3), libgpsmm(3), gpsprof(1),
277 gpsfake(1), gpsctl(1), gpscat(1). gpspipe(1).
278
280 Eric S. Raymond <esr@thyrsus.com>.
281The GPSD Project 6 December 2020 GPSMON(1)