1132451Sroberto<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2132451Sroberto 3132451Sroberto<html> 4132451Sroberto 5182007Sroberto <head> 6182007Sroberto <meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1"> 7182007Sroberto <meta name="GENERATOR" content="Mozilla/4.76 [en] (X11; U; Linux 2.2.16-22 i586) [Netscape]"> 8182007Sroberto <title>Generic NMEA GPS Receiver</title> 9182007Sroberto <link href="scripts/style.css" type="text/css" rel="stylesheet"> 10182007Sroberto </head> 11132451Sroberto 12182007Sroberto <body> 13182007Sroberto <h3>Generic NMEA GPS Receiver</h3> 14182007Sroberto <hr> 15182007Sroberto <h4>Synopsis</h4> 16182007Sroberto <p>Address: 127.127.20.<i>u</i><br> 17182007Sroberto Reference ID: <tt>GPS</tt><br> 18182007Sroberto Driver ID: <tt>GPS_NMEA</tt><br> 19182007Sroberto Serial Port: <tt>/dev/gps<i>u</i></tt>; 4800 baud, 8-bits, no parity<br> 20182007Sroberto Serial Port: <tt>/dev/gps<i>u</i></tt>; symlink to server:port (for nmead) Features: <tt>tty_clk</tt></p> 21182007Sroberto <h4>Description</h4> 22182007Sroberto <p>This driver supports GPS receivers with the <tt>$GPRMC</tt> NMEA output string by default. Alternately the <tt>$GPGGA</tt> or <tt>$GPGLL </tt>may be selected.</p> 23182007Sroberto <p>The driver expects the receiver to be set up to transmit a <tt>$GPRMC</tt> message every second.</p> 24182007Sroberto <p>The accuracy depend on the receiver used. Inexpesive GPS models are available with a claimed PPS signal accuracy of 1 <font face="Symbol">m</font>s or better relative to the broadcast signal. However, in most cases the actual accuracy is limited by the precision of the timecode and the latencies of the serial interface and operating system.</p> 25182007Sroberto <p>If the Operating System supports the PPSAPI, RFC-2783, it will be used.<br> </p> 26182007Sroberto <p>The various GPS sentences that this driver recognises look like this:<br> 27182007Sroberto (others quietly ignored)</p> 28182007Sroberto <pre><tt>$GPRMC,POS_UTC,POS_STAT,LAT,LAT_REF,LON,LON_REF,SPD,HDG,DATE,MAG_VAR,MAG_REF*CC<cr><lf> 29132451Sroberto$GPGLL,LAT,LAT_REF,LONG,LONG_REF,POS_UTC,POS_STAT*CC<cr><lf> 30132451Sroberto$GPGGA,POS_UTC,LAT,LAT_REF,LONG,LONG_REF,FIX_MODE,SAT_USED,HDOP,ALT,ALT_UNIT,GEO,G_UNIT,D_AGE,D_REF*CC<cr><lf> 31132451Sroberto 32132451Sroberto POS_UTC - UTC of position. Hours, minutes and seconds [fraction (opt.)]. (hhmmss[.fff]) 33132451Sroberto POS_STAT - Position status. (A = Data valid, V = Data invalid) 34132451Sroberto LAT - Latitude (llll.ll) 35132451Sroberto LAT_REF - Latitude direction. (N = North, S = South) 36132451Sroberto LON - Longitude (yyyyy.yy) 37132451Sroberto LON_REF - Longitude direction (E = East, W = West) 38132451Sroberto SPD - Speed over ground. (knots) (x.x) 39132451Sroberto HDG - Heading/track made good (degrees True) (x.x) 40132451Sroberto DATE - Date (ddmmyy) 41132451Sroberto MAG_VAR - Magnetic variation (degrees) (x.x) 42132451Sroberto MAG_REF - Magnetic variation (E = East, W = West) 43132451Sroberto FIX_MODE - Position Fix Mode ( 0 = Invalid, >0 = Valid) 44132451Sroberto SAT_USED - Number Satellites used in solution 45132451Sroberto HDOP - Horizontal Dilution of Precision 46132451Sroberto ALT - Antenna Altitude 47132451Sroberto ALT_UNIT - Altitude Units (Metres/Feet) 48132451Sroberto GEO - Geoid/Elipsoid separation 49132451Sroberto G_UNIT - Geoid units (M/F) 50132451Sroberto D_AGE - Age of last DGPS Fix 51132451Sroberto D_REF - Reference ID of DGPS station 52132451Sroberto CC - Checksum (optional) 53132451Sroberto <cr><lf> - Sentence terminator.</tt></pre> 54182007Sroberto Alternate GPS sentences (other than <tt>$GPRMC</tt> - the default) may be enabled by setting the relevent bits of 'mode' in the server configuration line<br> * server 127.127.20.x mode X<br> bit 0 - enables RMC ( value = 1)<br> bit 1 - enables GGA ( value = 2)<br> bit 2 - enables GLL ( value = 4)<br> 55182007Sroberto multiple sentences may be selected<br> 56182007Sroberto <p>The driver will send a <tt>$PMOTG,RMC,0000*1D<cr><lf></tt> message each time a <tt>$GPRMC</tt> string is needed. This is not needed on most GPS receivers because they automatically send the <tt>$GPRMC</tt> string every second and will only work on GPS receivers that understand the <tt>$PMOTG</tt> string. Others will just ignore it.</p> 57182007Sroberto <h4>Setting up the Garmin GPS-25XL</h4> 58182007Sroberto Switch off all output with by sending it the following string. 59182007Sroberto <pre>"$PGRMO,,2<cr><lf>"</pre> 60182007Sroberto <p>Now switch only $GPRMC on by sending it the following string.</p> 61182007Sroberto <pre>"$PGRMO,GPRMC,1<cr><lf>"</pre> 62182007Sroberto <p>On some systems the PPS signal isn't switched on by default. It can be switched on by sending the following string.</p> 63182007Sroberto <pre>"$PGRMC,,,,,,,,,,,,2<cr><lf>"</pre> 64182007Sroberto <h4>Monitor Data</h4> 65182007Sroberto <p>The GPS sentence(s) that is used is written to the clockstats file.</p> 66182007Sroberto <h4>Fudge Factors</h4> 67182007Sroberto <dl> 68182007Sroberto <dt><tt>time1 <i>time</i></tt> 69182007Sroberto <dd>Specifies the time offset calibration factor, in seconds and fraction, with default 0.0. 70182007Sroberto <dt><tt>time2 <i>time</i></tt> 71182007Sroberto <dd>Not used by this driver. 72182007Sroberto <dt><tt>stratum <i>number</i></tt> 73182007Sroberto <dd>Specifies the driver stratum, in decimal from 0 to 15, with default 0. 74182007Sroberto <dt><tt>refid <i>string</i></tt> 75182007Sroberto <dd>Specifies the driver reference identifier, an ASCII string from one to four characters, with default <tt>GPS</tt>. 76182007Sroberto <dt><tt>flag1 0 | 1</tt> 77182007Sroberto <dd>Not used by this driver. 78182007Sroberto <dt><tt>flag2 0 | 1</tt> 79182007Sroberto <dd>Specifies the PPS signal on-time edge: 0 for assert (default), 1 for clear. 80182007Sroberto <dt><tt>flag3 0 | 1</tt> 81182007Sroberto <dd>Controls the kernel PPS discipline: 0 for disable (default), 1 for enable. 82182007Sroberto <dt><tt>flag4 0 | 1</tt> 83182007Sroberto <dd>Not used by this driver. 84182007Sroberto </dl> 85182007Sroberto <p>Additional Information</p> 86182007Sroberto <p><a href="../refclock.html">Reference Clock Drivers</a></p> 87182007Sroberto <hr> 88182007Sroberto <script type="text/javascript" language="javascript" src="scripts/footer.txt"></script> 89182007Sroberto </body> 90132451Sroberto 91132451Sroberto</html>