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.
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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
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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
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