NAME

       gpsctl - control the modes of a GPS

SYNOPSIS

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

DESCRIPTION

       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:

       -b
           Put the GPS into native (binary) mode.

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

       -e
           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.

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

       -l
           List a table showing which option switches can be applied to which device types, and
           exit.

       -n
           Put GPS into NMEA mode.

       -s
           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.

       -t
           Force the device type.

       -x
           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.

       -T
           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
           second.

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

       -h
           Display program usage and exit.

       -D
           Set level of debug messages.

       -V
           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.

ENVIRONMENT VARIABLES

       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.

EXAMPLES

       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.

BUGS

       SiRF GPSes can only be identified by the success of an attempt to flip them into SiRF
       binary mode. Thus, the process of probing one of these running in NMEA will change its
       behavior.

       Baud rate and mode changes work in direct mode but are not reliable in client mode. This
       will be fixed in a future release.

SEE ALSO

       gpsd(8), gpsdctl(8), gps(1), libgps(3), libgpsmm(3), gpsprof(1), gpsfake(1).

AUTHOR

       Eric S. Raymond <esr@thyrsus.com>.