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gpsctl - control the modes of a GPS


gpsctl [-h] [-b | -n] [-x control] [-e] [-f] [-l] [-s speed] [-t devicetype] [-R]
[-D debuglevel] [-V] [serial-port]


gpsctl can switch a dual-mode GPS between NMEA and vendor-binary modes. It can also be
used to set the device baudrate. Note: Not all devices have these capabilities.

If you have only one GPS attached to your machine, and gpsd is running, it is not
necessary to specify the device; gpsctl does its work through gpsd, which will locate it
for you.

When gpsd is not running, the device specification is required, and you will need to be
running as root or be a member of the device's owning group in order to have write access
to the device. On many Unix variants the owning group will be named 'dialout'.

The program accepts the following options:

Put the GPS into native (binary) mode.

Change the GPS's cycle time. Units are seconds. Note, most GPSes have a fixed cycle
time of 1 second.

Generate the packet from any other arguments specified and ship it to standard output
instead of the device. This switch can be used with the -t option without specifying a
device. Note: the packet data for a binary prototype will be raw, not ASCII-ized in
any way.

Force low-level access (not through the daemon).

List a table showing which option switches can be applied to which device types, and

Put GPS into NMEA mode.

Set the baud rate at which the GPS emits packets.

Use this option with caution. On USB and Bluetooth GPSes 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.

Force the device type.

Send a specified control string to the GPS; gpsctl will provide packet headers and
trailers and checksum as appropriate for binary packet types, and whatever checksum
and trailer is required for text packet types. (You must include the leading $ for
NMEA packets.) When sending to a UBX device, the first two bytes of the string
supplied will become the message class and type, and the remainder the payload. When
sending to a Navcom NCT or Trimble TSIP device, the first byte is interpreted as the
command ID and the rest as payload. When sending to a Zodiac device, the first two
bytes are used as a message ID of type little-endian short, and the remainder as
payload in byte pairs interpreted as little-endian short. For all other supported
binary GPSes (notably including SiRF) the string is taken as the entire message
payload and wrapped with appropriate header, trailer and checksum bytes. C-style
backslash escapes in the string, notably \xNN for hex, will be interpreted;
additionally, \e will be replaced with ESC. This switch implies -f.

Change the sampling timeout. Defaults to 8 seconds, which should always be sufficient
to get an identifying packet from a device emitting at the normal rate of 1 per

Remove the GPSD shared-memory segment used for SHM export. This option will normally
only be of interest to GPSD developers.

Display program usage and exit.

Set level of debug messages.

Display program version and exit.

The argument of the forcing option, -t, should be a string which is contained in exactly
one of the known driver names; for a list, do gpsctl -l.

Forcing the device type behaves somewhat differently depending on whether this tool is
going through the daemon or not. In high-level mode, if the device that daemon selects for
you doesn't match the driver you specified, gpsctl exits with a warning. (This may be
useful in scripts.)

In low-level mode, if the device identifies as a Generic NMEA, use the selected driver
instead. This will be useful if you have a GPS device of known type that is in NMEA mode
and not responding to probes. (This option was originally implemented for talking to
SiRFStar I chips, which don't respond to the normal SiRF ID probe.)

If no options are given, the program will display a message identifying the GPS type of
the selected device and exit.

Reset (-r) operations must stand alone; others can be combined. Multiple options will be
executed in this order: mode changes (-b and -n) first, speed changes (-s) second, and
control-string sends (-c) last.


By setting the environment variable GPSD_SHM_KEY, you can control the key value used to
designate the shared-memory segment removed with the -R option. This will be useful mainly
when isolating test instances of gpsd from production ones.


gpsctl /dev/ttyUSB0
Attempt to identify the device on USB serial device 0. Time out after the default
number of seconds. Adding the -f will force low-level access and suppress the normal
complaint when this tool can't find a GPSD to work through.

gpsctl -f -n -s 9600 /dev/ttyUSB0
Use low-level operations (not going through a gpsd instance) to switch a GPS to NMEA
mode at 9600bps. The tool will identify the GPS type itself.

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