GPSFS(8)                                                 GPSFS(8)

     NAME
          gpsfs, gpsevermore - GPS time and position service

     SYNOPSIS
          aux/gpsfs [ -d device ] [ -b baud ] [ -s srvname ] [ -m
          mntpt ]

          aux/gpsevermore [ -d device ] [ -b baud ] [ -n baud ] [ -l
          location ]

     DESCRIPTION
          Aux/gpsfs reads an NMEA-compatible serial GPS (Global Posi-
          tioning System) device and provides time and position
          through a file system, by default mounted on /mnt and imple-
          menting /mnt/gps.

          It implements four files in the gps directory: position,
          time, satellites, and raw.

          The read-only position file contains one line of information
          in 9 tab-separated fields:

          fix quality         0 means position data invalid, 1 means a
                              2D position is available, 2 means a 3D
                              position is available.  The value is 8,
                              9, or 10, respectively, when the fix
                              data comes from a file rather than an
                              actual GPS.

          zulu time           universal coordinated time encoded as
                              hhmmss followed by the character 'Z'.

          system time         time and date converted to the format of
                              time(2).

          longitude           in degrees, east of Greenwich is posi-
                              tive, west negative.

          latitude            in degrees, positive is north, negative
                              south of the equator.

          altitude            above sea level, in meters.

          course              degrees, clockwise from true north.

          ground speed        in km/h

          magnetic deviation  (not provided by all GPSs), in degrees,
                              positive is westerly, negative easterly.

     GPSFS(8)                                                 GPSFS(8)

          The read-only time file contains one line of information in
          4 tab-separated fields:

          gps time     in time(2) format.

          gps time     in nsec (see time(2)) format (ms accuracy).

          system time  in nsec format.  This is the system time at the
                       time of the gps time sample.  The difference
                       between this and the previous field is used in
                       clock synchronization.  See timesync(8).

          validity     the character A meaning sample valid and usable
                       for clock synchronization.  The other values
                       are not usable for clock sync: B means valid
                       sample from file playback, V means invalid sam-
                       ple, and W means invalid playback sample.

          The read-only satellites file contains information about the
          current satellite constellation.  It consists of one line of
          general information, followed by zero or more lines, one for
          each satellite in use.  The first line contains two fields:

          fix quality         same as in the position file.

          satellites in view  number of satellites above the horizon

          Subsequent lines have four fields:

          prn        satellite ID

          elevation  above the horizon, degrees.

          azimuth    direction, degrees from true north

          snr        Signal to noise ratio, 0 - 99 dB

          The contents of these files are refreshed once per second
          when reading from an actual GPS, and once per 100 ms (giving
          a speed up of a factor 10) when playing back from file.

          The read-only raw file can be read to obtain a copy of the
          raw NMEA GPS output.  Gpsfs keeps an internal buffer of 8KB,
          so the reader must keep up with the output (typically 500 or
          so bytes per second).

          The -d flag establishes the device the GPS samples are read
          from.  If the device file is not a serial interface, gpsfs
          assumes playback from file and modifies quality parameters

     GPSFS(8)                                                 GPSFS(8)

          as such.

          The -b flag specifies the baud rate of the serial line.  The
          standard baud rate for NMEA GPS is 4800 baud, but many
          device allow changing to higher speeds.

          The -s flag specifies the name under which the gpsfs service
          is posted in /srv.

          The -m flag specifies a mount other than /mnt.

        Evermore
          Aux/gpsevermore is used to configure GPSs using an Evermore
          chipset.

          The -d flag specifies the serial device to the GPS.

          The -b flag specifies the baud rate of the serial line.  The
          standard baud rate for NMEA GPS is 4800 baud, but many
          device allow changing to higher speeds.

          The -n flag specifies the speed to set the GPS to.  When the
          command finishes, the GPS should be read (and configured) at
          the new speed.

          The -l flag is sued to specify the location to initialize
          the GPS to.  The format is dd:mm:ssX or dd:mm.mmmX or
          dd.dddX, where dd stands for degrees (one or more digits),
          mm for minutes and ss for seconds of arc.  X is one of W, E,
          N or S.  Longitudes come with W or E, latitudes with N or S.
          The -l flag is followed by two such fields, one for longi-
          tude, one for latitude.  They may be given in a single argu-
          ment (separated by white space), or in two arguments, in
          either order.  Initialization time is taken from time(2).

     SEE ALSO
          timesync(8), time(2)

     FILES
          /mnt/gps/position    position, time, speed and heading
          /mnt/gps/satellites  satellites in view
          /mnt/gps/time        GPS time (millisecond accuracy)
          /dev/eia0            default GPS device

     SOURCE
          /sys/src/cmd/aux/gps