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+.TH GPSFS 8
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+.SH NAME
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+gpsfs, gpsevermore \- GPS time and position service
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+.SH SYNOPSIS
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+.B aux/gpsfs
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+[
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+.B -d
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+.I device
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+]
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+[
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+.B -b
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+.I baud
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+]
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+[
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+.B -s
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+.I srvname
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+]
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+[
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+.B -m
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+.I mntpt
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+]
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+.PP
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+.B aux/gpsevermore
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+[
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+.B -d
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+.I device
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+]
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+[
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+.B -b
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+.I baud
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+]
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+[
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+.B -n
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+.I baud
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+]
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+[
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+.B -l
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+.I location
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+]
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+.SH DESCRIPTION
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+.B Aux/gpsfs
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+reads an NMEA-compatible serial GPS device and provides time and position
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+through a file system, typically in
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+.BR /mnt/gps .
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+.PP
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+It implements four files in the
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+.B gps
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+directory:
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+.BR position ,
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+.BR time ,
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+.BR satellites ,
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+and
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+.BR raw .
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+.PP
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+The read-only
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+.B position
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+file contains one line of information in 9 tab-separated fields:
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+.TP
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+.I "fix quality
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+0 means position data invalid, 1 means a 2D position is available, 2 means a 3D position is available.
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+The value is 8, 9, or 10, respectively, when the fix data comes from a file rather than an actual GPS.
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+.TP
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+.I "zulu time
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+universal coordinated time encoded as hhmmss followed by the character 'Z'.
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+.TP
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+.I "system time
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+time and date converted to the format of
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+.IR time (2).
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+.TP
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+.I longitude
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+in degrees, east of Greenwich is positive, west negative.
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+.TP
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+.I latitude
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+in degrees, positive is north, negative south of the equator.
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+.TP
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+.I altitude
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+above sea level, in meters.
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+.TP
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+.I course
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+degrees, clockwise from true north.
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+.TP
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+.I "ground speed
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+in km/h
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+.TP
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+.I "magnetic deviation
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+(not provided by all GPSs), in degrees, positive is westerly, negative easterly.
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+.PP
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+The read-only
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+.B time
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+file contains one line of information in 4 tab-separated fields:
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+.TP
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+.I "gps time
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+in
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+.IR time (2)
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+format.
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+.TP
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+.I "gps time
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+in
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+.IR nsec (2)
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+format (ms accuracy).
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+.TP
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+.I "system time
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+in
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+.IR nsec (2)
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+format. This is the system time at the time of the
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+.I "gps time
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+sample. The difference between this and the previous field is used in clock
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+synchronization. See
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+.IR timesync (8).
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+.TP
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+.I validity
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+the character
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+.B A
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+meaning sample valid and usable for clock synchronization. The other values are
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+not usable for clock sync:
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+.B B
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+means valid sample from file playback,
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+.B V
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+means invalid sample, and
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+.B W
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+means invalid playback sample.
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+.PP
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+The read-only
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+.B satellites
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+file contains information about the current satellite constellation. It consists
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+of one line of general information, followed by zero or more lines, one for each satellite in use.
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+The first line contains two fields:
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+.TP
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+.I "fix quality
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+same as in the
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+.B position
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+file.
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+.TP
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+.I "satellites in view
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+number of satellites above the horizon
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+.PP
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+Subsequent lines have four fields:
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+.TP
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+.I prn
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+satellite ID
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+.TP
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+.I elevation
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+above the horizon, degrees.
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+.TP
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+.I azimuth
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+direction, degrees from true north
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+.TP
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+.I snr
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+Signal to noise ratio, 0 - 99 dB
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+.PP
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+The contents of these files are refreshed once per second when reading from an actual GPS,
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+and once per 100 ms (giving a speed up of a factor 10) when playing back from file.
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+.PP
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+The read-only
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+.B raw
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+file can be read to obtain a copy of the raw NMEA GPS output.
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+.I Gpsfs
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+keeps an internal buffer of 8KB, so the reader must keep up with the output
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+(typically 500 or so bytes per second).
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+.PP
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+The
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+.B \-d
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+flag establishes the device the GPS samples are read from. If the device file is not
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+a serial interface,
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+.I gpsfs
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+assumes playback from file and modifies quality parameters as such.
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+.PP
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+The
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+.B \-b
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+flag specifies the baud rate of the serial line. The standard baud rate for NMEA
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+GPS is 4800 baud, but many device allow changing to higher speeds.
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+.PP
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+The
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+.B \-s
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+flag specifies the name under which the
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+.I gpsfs
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+service is posted in
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+.BR /srv .
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+.PP
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+The
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+.B \-m
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+flag specifies a mount mount other than
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+.BR /mnt .
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+.PP
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+.B Aux/gpsevermore
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+is used to configure GPSs using an Evermore chipset.
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+.PP
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+The
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+.B \-d
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+flag specifies the serial device to the GPS.
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+.PP
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+The
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+.B \-b
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+flag specifies the baud rate of the serial line. The standard baud rate for NMEA
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+GPS is 4800 baud, but many device allow changing to higher speeds.
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+.PP
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+The
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+.B \-n
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+flag specifies the speed to set the GPS to. When the command finishes, the
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+GPS should be read (and configured) at the new speed.
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+.PP
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+The
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+.B \-l
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+flag is sued to specify the location to initialize the GPS to. The format is
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+.B dd:mm:ssX
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+or
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+.B dd:mm.mmmX
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+or
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+.BR dd.dddX ,
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+where
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+.B dd
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+stands for degrees (one or more digits),
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+.B mm
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+for minutes and
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+.B ss
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+for seconds of arc.
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+.B X
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+is one of
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+.BR W ,
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+.BR E ,
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+.B N
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+or
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+.BR S .
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+Longitudes come with
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+.B W
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+or
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+.BR E ,
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+latitudes with
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+.B N
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+or
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+.BR S .
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+The
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+.B \-l
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+flag is followed by two such fields, one for longitude, one for latitude. They may be
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+given in a single argument (separated by white space), or in two arguments, in either order.
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+Initialization time is taken from
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+.IR time (2).
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+.SH "SEE ALSO
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+.IR timesync (2),
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+.IR time (2),
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+.IR nsec (2).
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+.SH FILES
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+.TF /mnt/gps/satellites
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+.TP
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+.B /mnt/gps/position
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+position, time, speed and heading
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+.TP
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+.B /mnt/gps/satellites
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+satellites in view
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+.TP
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+.B /mnt/gps/time
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+GPS time (millisecond accuracy)
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+.TP
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+.B /dev/eia0
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+default GPS device
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+.SH SOURCE
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+.B /sys/src/cmd/aux/gps
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David du Colombier