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+ <h3>GPSD NG client driver</h3>
+ <hr>
+ <h4>Synopsis</h4>
+
+ <p>
+ Address: 127.127.46.<i>u</i><br>
+ Reference ID: <tt>GPSD</tt><br>
+ Driver ID: <tt>GPSD_JSON</tt><br>
+ Serial Port: <tt>/dev/gps<i>u</i></tt> as symlink to the true
+ device (not used directly; see below)<br>
+ Features: <tt></tt>
+ </p>
+
+ <h4>Description</h4>
+
+ <p>
+ This driver is a client driver to the GPSD daemon, which over
+ the time became increasingly popular for UN*Xish platforms. GPSD
+ can manage several devices in parallel, aggregate information,
+ and acts as a data hub for client applications. GPSD can also
+ auto-detect and handle PPS hardware signals on serial
+ ports. Have a look at <a href="http://www.catb.org/gpsd/">the
+ GPSD project page</a>.
+ </p>
+ <p>
+ <b>It is imortant to understand that this driver needs a GPS
+ device with PPS support to operate.</b>
+ </p>
+ <p>
+ The GPSD-NG protocol is text based, using JSON notation to
+ transfer records in form of JSON objects. The driver uses a
+ TCP/IP connection to <tt>localhost:gpsd</tt> to connect to the
+ daemon and then requests the GPS device <tt>/dev/gps<i>u</i></tt>
+ to be watched. (Different clock units use different devices, and
+ GPSD is able to give only the relevant information to a clock
+ instance.)
+ </p>
+ <p>
+ This driver does not expect GPSD running or the clock device to
+ be present <i>a priori</i>; it will try to re-establish a lost
+ or hitherto unsuccessful connection. There is a 10 seconds delay
+ between a connection loss or failed attempt and the next
+ reconnect attempt; this makes sure that there is no thrashing on
+ the network layer.
+ </p>
+ <p>
+ The overall accuracy depends on the receiver used. The driver
+ uses the error estimations (95% probability limits) provided by
+ GPSD to set the clock precision dynamically according to these
+ readings.
+ </p>
+ <p>
+ The driver needs the VERSION, TPV and PPS objects of the GPSD
+ protocol. (Others are quietly ignored.)
+ </p>
+
+
+ <h4>Naming a Device</h4>
+ <p>
+ The GPSD driver uses the same name as the NMEA driver,
+ namely <tt>/dev/gps<i>u</i></tt>. There is a simple reason for
+ that: While the NMEA driver and the GPSD driver can be active at
+ the same time <strong>for different devices</strong>, they
+ cannot access the same device at a time. Having the same name
+ helps on that. It also eases migration from using NMEA directly
+ to using GPSD, as no new links etc need to be created.
+
+ GPSD is normally started with the device name to access; it can
+ also be instructed by hotplug scripts to add or remove devices
+ from its device pool. Luckily, the symlinks used by the NMEA
+ driver are happily accepted and used by GPSD; this makes it
+ possible to use the symlink names as device identification.
+
+ <h4>The 'mode' byte</h4>
+ <p>
+ Until now, GPSD has no mode bits.
+ </p>
+
+ <h4>Fudge Factors</h4>
+
+ <dl>
+ <dt><tt>time1 <i>time</i></tt></dt>
+ <dd>Specifies the PPS time offset calibration factor, in seconds and fraction, with default 0.0.</dd>
+ <dt><a name="fudgetime2"><tt>time2 <i>time</i></tt></a></dt>
+ <dd><it>(not used)</it></dd>
+ <dt><tt>stratum <i>number</i></tt></dt>
+ <dd>Specifies the driver stratum, in decimal from 0 to 15, with default 0.</dd>
+ <dt><tt>refid <i>string</i></tt></dt>
+ <dd>Specifies the driver reference identifier, an ASCII string from one to four characters, with
+ default <tt>GPS</tt>.</dd>
+ <dt><tt>flag1 0 | 1</tt></dt><dd><it>(not used)</it></dd>
+ <dt><tt>flag2 0 | 1</tt></dt><dd><it>(not used)</it></dd>
+ <dt><tt>flag3 0 | 1</tt></dt><dd><it>(not used)</it></dd>
+ <dt><tt>flag4 0 | 1</tt></dt><dd><it>(not used)</it></dd>
+ </dl>
+
+ <p>Additional Information</p>
+ <p><a href="../refclock.html">Reference Clock Drivers</a></p>
+ <hr>
+ <script type="text/javascript" language="javascript" src="scripts/footer.txt"></script>
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projects / thirdparty / ntp.git / commitdiff
