Subversion Repositories planix.SVN

.TH GPSFS 8

.SH NAME

gpsfs, gpsevermore \- GPS time and position service

.SH SYNOPSIS

.B aux/gpsfs

[

.B -d

.I device

]

[

.B -b

.I baud

]

[

.B -s

.I srvname

]

[

.B -m

.I mntpt

]

.PP

.B aux/gpsevermore

[

.B -d

.I device

]

[

.B -b

.I baud

]

[

.B -n

.I baud

]

[

.B -l

.I location

]

.SH DESCRIPTION

.B Aux/gpsfs

reads an NMEA-compatible serial GPS (Global Positioning System)

device and provides time and position

through a file system, by default mounted on

.B /mnt

and implementing

.BR /mnt/gps .

.PP

It implements four files in the

.B gps

directory:

.BR position ,

.BR time ,

.BR satellites ,

and

.BR raw .

.PP

The read-only

.B position

file contains one line of information in 9 tab-separated fields:

.TF "\fImagnetic deviation

.PD

.TP

.I "fix quality

The value is 8, 9, or 10, respectively, when the fix data comes from a file rather than an actual GPS.

.TP

.I "zulu time

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

.TP

.I "system time

time and date converted to the format of

.IR time (2).

.TP

.I longitude

in degrees, east of Greenwich is positive, west negative.

.TP

.I latitude

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

.TP

.I altitude

above sea level, in meters.

.TP

.I course

degrees, clockwise from true north.

.TP

.I "ground speed

in km/h

.TP

.I "magnetic deviation

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

.PP

The read-only

.B time

file contains one line of information in 4 tab-separated fields:

.TF "\fIsystem time

.PD

.TP

.I "gps time

in

.IR time (2)

format.

.TP

.I "gps time

in

.I nsec

(see

.IR time (2))

format (ms accuracy).

.TP

.I "system time

in

.I nsec

format.  This is the system time at the time of the

.I "gps time

sample.  The difference between this and the previous field is used in clock

synchronization.  See

.IR timesync (8).

.TP

.I validity

the character

.B A

meaning sample valid and usable for clock synchronization.  The other values are

not usable for clock sync:

.B B

means valid sample from file playback,

.B V

means invalid sample, and

.B W

means invalid playback sample.

.PP

The read-only

.B 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:

.TF "\fIsatellites in view

.PD

.TP

.I "fix quality

same as in the

.B position

file.

.TP

.I "satellites in view

number of satellites above the horizon

.PP

Subsequent lines have four fields:

.TF "\fIelevation

.PD

.TP

.I prn

satellite ID

.TP

.I elevation

above the horizon, degrees.

.TP

.I azimuth

direction, degrees from true north

.TP

.I snr

Signal to noise ratio, 0 - 99 dB

.PP

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.

.PP

The read-only

.B raw

file can be read to obtain a copy of the raw NMEA GPS output.

.I Gpsfs

keeps an internal buffer of 8KB, so the reader must keep up with the output

(typically 500 or so bytes per second).

.PP

The

.B \-d

flag establishes the device the GPS samples are read from.  If the device file is not

a serial interface,

.I gpsfs

assumes playback from file and modifies quality parameters as such.

.PP

The

.B \-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.

.PP

The

.B \-s

flag specifies the name under which the

.I gpsfs

service is posted in

.BR /srv .

.PP

The

.B \-m

flag specifies a mount mount other than

.BR /mnt .

.SS Evermore

.B Aux/gpsevermore

is used to configure GPSs using an Evermore chipset.

.PP

The

.B \-d

flag specifies the serial device to the GPS.

.PP

The

.B \-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.

.PP

The

.B \-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.

.PP

The

.B \-l

flag is sued to specify the location to initialize the GPS to.  The format is

.B dd:mm:ssX

or

.B dd:mm.mmmX

or

.BR dd.dddX ,

where

.B dd

stands for degrees (one or more digits),

.B mm

for minutes and

.B ss

for seconds of arc.

.B X

is one of

.BR W ,

.BR E ,

.B N

or

.BR S .

Longitudes come with

.B W

or

.BR E ,

latitudes with

.B N

or

.BR S .

The

.B \-l

flag is followed by two such fields, one for longitude, one for latitude.  They may be

given in a single argument (separated by white space), or in two arguments, in either order.

Initialization time is taken from

.IR time (2).

.SH "SEE ALSO

.IR timesync (8),

.IR time (2)

.SH FILES

.TF /mnt/gps/satellites

.TP

.B /mnt/gps/position

position, time, speed and heading

.TP

.B /mnt/gps/satellites

satellites in view

.TP

.B /mnt/gps/time

GPS time (millisecond accuracy)

.TP

.B /dev/eia0

default GPS device

.SH SOURCE

.B /sys/src/cmd/aux/gps