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6 <title>Generic NMEA GPS Receiver
12 Generic NMEA GPS Receiver</h3>
17 Address: 127.127.20.<i>u</i>
18 <br>Reference ID: <tt>GPS</tt>
19 <br>Driver ID: <tt>GPS_NMEA</tt>
20 <br>Serial Port: <tt>/dev/gps<i>u</i></tt>; 4800 baud, 8-bits, no parity
21 <br>Features: <tt>tty_clk</tt>
24 This driver supports GPS receivers with the <tt>$GPRMC</tt> NMEA output
25 string by default. Alternately the <tt>$GPGGA</tt> or <tt>$GPGLL
28 <br>The driver expects the receiver to be set up to transmit a <tt>$GPRMC</tt>
30 <p>The accuracy depend on the receiver used. Inexpesive GPS models are
31 available with a claimed PPS signal accuracy of 1 <font face="Symbol">m</font>s
32 or better relative to the broadcast signal. However, in most cases the
33 actual accuracy is limited by the precision of the timecode and the latencies
34 of the serial interface and operating system.
35 <p>If the Operating System supports the PPSAPI, RFC-2783, it will be used.
37 <p>The various GPS sentences that this driver recognises look like this:
38 <br>(others quietly ignored)
39 <pre><tt>$GPRMC,POS_UTC,POS_STAT,LAT,LAT_REF,LON,LON_REF,SPD,HDG,DATE,MAG_VAR,MAG_REF*CC<cr><lf>
40 $GPGLL,LAT,LAT_REF,LONG,LONG_REF,POS_UTC,POS_STAT*CC<cr><lf>
41 $GPGGA,POS_UTC,LAT,LAT_REF,LONG,LONG_REF,FIX_MODE,SAT_USED,HDOP,ALT,ALT_UNIT,GEO,G_UNIT,D_AGE,D_REF*CC<cr><lf>
43 POS_UTC - UTC of position. Hours, minutes and seconds [fraction (opt.)]. (hhmmss[.fff])
44 POS_STAT - Position status. (A = Data valid, V = Data invalid)
45 LAT - Latitude (llll.ll)
46 LAT_REF - Latitude direction. (N = North, S = South)
47 LON - Longitude (yyyyy.yy)
48 LON_REF - Longitude direction (E = East, W = West)
49 SPD - Speed over ground. (knots) (x.x)
50 HDG - Heading/track made good (degrees True) (x.x)
51 DATE - Date (ddmmyy)
52 MAG_VAR - Magnetic variation (degrees) (x.x)
53 MAG_REF - Magnetic variation (E = East, W = West)
54 FIX_MODE - Position Fix Mode ( 0 = Invalid, >0 = Valid)
55 SAT_USED - Number Satellites used in solution
56 HDOP - Horizontal Dilution of Precision
57 ALT - Antenna Altitude
58 ALT_UNIT - Altitude Units (Metres/Feet)
59 GEO - Geoid/Elipsoid separation
60 G_UNIT - Geoid units (M/F)
61 D_AGE - Age of last DGPS Fix
62 D_REF - Reference ID of DGPS station
63 CC - Checksum (optional)
64 <cr><lf> - Sentence terminator.</tt></pre>
65 Alternate GPS sentences (other than <tt>$GPRMC</tt> - the default) may
66 be enabled by setting the relevent bits of 'mode' in the server configuration
68 <br> * server 127.127.20.x mode X
69 <br> bit 0 - enables RMC ( value =
71 <br> bit 1 - enables GGA ( value =
73 <br> bit 2 - enables GLL
75 <br>multiple sentences may be selected
77 <p>The driver will send a <tt>$PMOTG,RMC,0000*1D<cr><lf></tt> message
78 each time a <tt>$GPRMC</tt> string is needed. This is not needed on most
79 GPS receivers because they automatically send the <tt>$GPRMC</tt> string
80 every second and will only work on GPS receivers that understand the <tt>$PMOTG</tt>
81 string. Others will just ignore it.
83 Setting up the Garmin GPS-25XL</h4>
84 Switch off all output with by sending it the following string.
85 <pre>"$PGRMO,,2<cr><lf>"</pre>
86 Now switch only $GPRMC on by sending it the following string.
87 <pre>"$PGRMO,GPRMC,1<cr><lf>"</pre>
88 On some systems the PPS signal isn't switched on by default. It can be
89 switched on by sending the following string.
90 <pre>"$PGRMC,,,,,,,,,,,,2<cr><lf>"</pre>
94 The GPS sentence(s) that is used is written to the clockstats file.
100 <tt>time1 <i>time</i></tt></dt>
103 Specifies the time offset calibration factor, in seconds and fraction,
104 with default 0.0.</dd>
107 <tt>time2 <i>time</i></tt></dt>
110 Not used by this driver.</dd>
113 <tt>stratum <i>number</i></tt></dt>
116 Specifies the driver stratum, in decimal from 0 to 15, with default 0.</dd>
119 <tt>refid <i>string</i></tt></dt>
122 Specifies the driver reference identifier, an ASCII string from one to
123 four characters, with default <tt>GPS</tt>.</dd>
126 <tt>flag1 0 | 1</tt></dt>
129 Not used by this driver.</dd>
132 <tt>flag2 0 | 1</tt></dt>
135 Specifies the PPS signal on-time edge: 0 for assert (default), 1 for clear.</dd>
138 <tt>flag3 0 | 1</tt></dt>
141 Controls the kernel PPS discipline: 0 for disable (default), 1 for enable.</dd>
144 <tt>flag4 0 | 1</tt></dt>
147 Not used by this driver.</dd>
153 <p>Additional Information
154 <p><a href="refclock.htm">Reference Clock Drivers</a></dl>
158 David L. Mills (mills@udel.edu)</address>