driver20.html revision 1.1.1.2
1 1.1 kardel <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2 1.1.1.2 christos <html><head> 3 1.1.1.2 christos <meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1"><title>Generic NMEA GPS Receiver</title> 4 1.1.1.2 christos 5 1.1.1.2 christos <link href="scripts/style.css" type="text/css" rel="stylesheet"> 6 1.1.1.2 christos <style type="text/css"> 7 1.1.1.2 christos table.dlstable { font-size:85%; } 8 1.1.1.2 christos td.ttf{ font-family:Courier; font-weight:bold; } 9 1.1.1.2 christos </style></head> 10 1.1 kardel 11 1.1 kardel 12 1.1 kardel 13 1.1.1.2 christos <body> 14 1.1.1.2 christos <h3>Generic NMEA GPS Receiver</h3> 15 1.1.1.2 christos <hr> 16 1.1.1.2 christos <h4>Synopsis</h4> 17 1.1.1.2 christos 18 1.1.1.2 christos <p> 19 1.1.1.2 christos Address: 127.127.20.<i>u</i><br> 20 1.1.1.2 christos Reference ID: <tt>GPS</tt><br> 21 1.1.1.2 christos Driver ID: <tt>GPS_NMEA</tt><br> 22 1.1.1.2 christos Serial Port: <tt>/dev/gps<i>u</i></tt>; 4800 - 115200 bps, 8-bits, no parity<br> 23 1.1.1.2 christos Serial Port: <tt>/dev/gpspps<i>u</i></tt>; for just the PPS signal (this 24 1.1.1.2 christos is tried first for PPS, before <tt>/dev/gps<i>u</i></tt>)<br> 25 1.1.1.2 christos Serial Port: <tt>/dev/gps<i>u</i></tt>; symlink to server:port (for nmead)<br> 26 1.1.1.2 christos Features: <tt>tty_clk</tt> 27 1.1.1.2 christos </p> 28 1.1.1.2 christos 29 1.1.1.2 christos <h4>Description</h4> 30 1.1.1.2 christos 31 1.1.1.2 christos <p> 32 1.1.1.2 christos This driver supports GPS receivers with 33 1.1.1.2 christos the <tt>$GPRMC</tt>, <tt>$GPGLL</tt>, <tt>$GPGGA</tt>, <tt>$GPZDA</tt> 34 1.1.1.2 christos and <tt>$GPZDG</tt> NMEA sentences by default. Note that Accord's 35 1.1.1.2 christos custom NMEA sentence <tt>$GPZDG</tt> reports using the GPS timescale, 36 1.1.1.2 christos while the rest of the sentences report UTC. The difference between 37 1.1.1.2 christos the two is a whole number of seconds which increases with each leap 38 1.1.1.2 christos second insertion in UTC. To avoid problems mixing UTC and GPS 39 1.1.1.2 christos timescales, the driver disables processing of UTC sentences 40 1.1.1.2 christos once <tt>$GPZDG</tt> is received. 41 1.1.1.2 christos </p> 42 1.1.1.2 christos <p> 43 1.1.1.2 christos The driver expects the receiver to be set up to transmit at least one 44 1.1.1.2 christos supported sentence every second. 45 1.1.1.2 christos </p> 46 1.1.1.2 christos <p> 47 1.1.1.2 christos The accuracy depends on the receiver used. Inexpensive GPS models are 48 1.1.1.2 christos available with a claimed PPS signal accuracy of 49 1.1.1.2 christos 1 μs or better relative to the broadcast 50 1.1.1.2 christos signal. However, in most cases the actual accuracy is limited by the 51 1.1.1.2 christos precision of the timecode and the latencies of the serial interface and 52 1.1.1.2 christos operating system. 53 1.1.1.2 christos </p> 54 1.1.1.2 christos <p> 55 1.1.1.2 christos If the Operating System supports PPSAPI 56 1.1.1.2 christos (<a href="http://www.ietf.org/rfc/rfc2783.txt">RFC 2783</a>), fudge flag1 57 1.1.1.2 christos 1 enables its use. 58 1.1.1.2 christos </p> 59 1.1.1.2 christos <p> 60 1.1.1.2 christos The various GPS sentences that this driver recognises look like this:<br> 61 1.1.1.2 christos (others quietly ignored) 62 1.1.1.2 christos </p> 63 1.1.1.2 christos 64 1.1.1.2 christos <p><table class="dlstable" border="1"> 65 1.1.1.2 christos <caption>Accepted NMEA sentences</caption> 66 1.1.1.2 christos <tbody><tr> 67 1.1.1.2 christos <th>Sentence</th> 68 1.1.1.2 christos <th>Vendor</th> 69 1.1.1.2 christos </tr><tr> 70 1.1.1.2 christos <td class="ttf">$GPRMC,UTC,POS_STAT,LAT,LAT_REF,LON,LON_REF,SPD,HDG,DATE,MAG_VAR,MAG_REF*CS<cr><lf></td> 71 1.1.1.2 christos </tr><tr> 72 1.1.1.2 christos <td class="ttf">$GPGLL,LAT,LAT_REF,LON,LON_REF,UTC,POS_STAT*CS<cr><lf></td> 73 1.1.1.2 christos </tr><tr> 74 1.1.1.2 christos <td class="ttf">$GPGGA,UTC,LAT,LAT_REF,LON,LON_REF,FIX_MODE,SAT_USED,HDOP,ALT,ALT_UNIT,GEO,G_UNIT,D_AGE,D_REF*CS<cr><lf></td> 75 1.1.1.2 christos </tr><tr> 76 1.1.1.2 christos <td class="ttf">$GPZDA,UTC,DD,MM,YYYY,TH,TM,*CS<cr><lf></td> 77 1.1.1.2 christos </tr><tr> 78 1.1.1.2 christos <td class="ttf">$GPZDG,GPSTIME,DD,MM,YYYY,AA.BB,V*CS<cr><lf></td> 79 1.1.1.2 christos <td>Accord</td> 80 1.1.1.2 christos </tr> 81 1.1.1.2 christos </tbody></table></p> 82 1.1.1.2 christos 83 1.1.1.2 christos <p><table class="dlstable" border="1"> 84 1.1.1.2 christos <caption>NMEA data items</caption> 85 1.1.1.2 christos <tbody><tr> 86 1.1.1.2 christos <th>Symbol</th> 87 1.1.1.2 christos <th>Meaning and Format</th> 88 1.1.1.2 christos </tr> 89 1.1.1.2 christos 90 1.1.1.2 christos <tr> 91 1.1.1.2 christos <td class="ttf">UTC</td> 92 1.1.1.2 christos <td>Time of day on UTC timescale. Hours, minutes and seconds [fraction (opt.)]. (hhmmss[.fff])</td> 93 1.1.1.2 christos </tr><tr> 94 1.1.1.2 christos <td class="ttf">POS_STAT</td> 95 1.1.1.2 christos <td>Position status. (A = Data valid, V = Data invalid)</td> 96 1.1.1.2 christos </tr><tr> 97 1.1.1.2 christos <td class="ttf">LAT</td> 98 1.1.1.2 christos <td>Latitude (llll.ll)</td> 99 1.1.1.2 christos </tr><tr> 100 1.1.1.2 christos <td class="ttf">LAT_REF</td> 101 1.1.1.2 christos <td>Latitude direction. (N = North, S = South)</td> 102 1.1.1.2 christos </tr><tr> 103 1.1.1.2 christos <td class="ttf">LON</td> 104 1.1.1.2 christos <td>Longitude (yyyyy.yy)</td> 105 1.1.1.2 christos </tr><tr> 106 1.1.1.2 christos <td class="ttf">LON_REF</td> 107 1.1.1.2 christos <td>Longitude direction (E = East, W = West)</td> 108 1.1.1.2 christos </tr><tr> 109 1.1.1.2 christos <td class="ttf">SPD</td> 110 1.1.1.2 christos <td>Speed over ground. (knots) (x.x)</td> 111 1.1.1.2 christos </tr><tr> 112 1.1.1.2 christos <td class="ttf">HDG</td> 113 1.1.1.2 christos <td>Heading/track made good (degrees True) (x.x)</td> 114 1.1.1.2 christos </tr><tr> 115 1.1.1.2 christos <td class="ttf">DATE</td> 116 1.1.1.2 christos <td>Date (ddmmyy)</td> 117 1.1.1.2 christos </tr><tr> 118 1.1.1.2 christos <td class="ttf">MAG_VAR</td> 119 1.1.1.2 christos <td>Magnetic variation (degrees) (x.x)</td> 120 1.1.1.2 christos </tr><tr> 121 1.1.1.2 christos <td class="ttf">MAG_REF</td> 122 1.1.1.2 christos <td>Magnetic variation (E = East, W = West)</td> 123 1.1.1.2 christos </tr><tr> 124 1.1.1.2 christos <td class="ttf">FIX_MODE</td> 125 1.1.1.2 christos <td>Position Fix Mode (0 = Invalid, >0 = Valid)</td> 126 1.1.1.2 christos </tr><tr> 127 1.1.1.2 christos <td class="ttf">SAT_USED</td> 128 1.1.1.2 christos <td>Number of Satellites used in solution</td> 129 1.1.1.2 christos </tr><tr> 130 1.1.1.2 christos <td class="ttf">HDOP</td> 131 1.1.1.2 christos <td>Horizontal Dilution of Precision</td> 132 1.1.1.2 christos </tr><tr> 133 1.1.1.2 christos <td class="ttf">ALT</td> 134 1.1.1.2 christos <td>Antenna Altitude</td> 135 1.1.1.2 christos </tr><tr> 136 1.1.1.2 christos <td class="ttf">ALT_UNIT</td> 137 1.1.1.2 christos <td>Altitude Units (Metres/Feet)</td> 138 1.1.1.2 christos </tr><tr> 139 1.1.1.2 christos <td class="ttf">GEO</td> 140 1.1.1.2 christos <td>Geoid/Elipsoid separation</td> 141 1.1.1.2 christos </tr><tr> 142 1.1.1.2 christos <td class="ttf">G_UNIT</td> 143 1.1.1.2 christos <td>Geoid units (M/F)</td> 144 1.1.1.2 christos </tr><tr> 145 1.1.1.2 christos <td class="ttf">D_AGE</td> 146 1.1.1.2 christos <td>Age of last DGPS Fix</td> 147 1.1.1.2 christos </tr><tr> 148 1.1.1.2 christos <td class="ttf">D_REF</td> 149 1.1.1.2 christos <td>Reference ID of DGPS station</td> 150 1.1.1.2 christos </tr><tr> 151 1.1.1.2 christos <td class="ttf">GPSTIME</td> 152 1.1.1.2 christos <td>Time of day on GPS timescale. Hours, minutes and seconds [fraction (opt.)]. (hhmmss[.f])</td> 153 1.1.1.2 christos </tr><tr> 154 1.1.1.2 christos <td class="ttf">DD</td> 155 1.1.1.2 christos <td>Day of the month (1-31)</td> 156 1.1.1.2 christos </tr><tr> 157 1.1.1.2 christos <td class="ttf">MM</td> 158 1.1.1.2 christos <td>Month of the year (1-12)</td> 159 1.1.1.2 christos </tr><tr> 160 1.1.1.2 christos <td class="ttf">YYYY</td> 161 1.1.1.2 christos <td>Year</td> 162 1.1.1.2 christos </tr><tr> 163 1.1.1.2 christos <td class="ttf">AA.BB</td> 164 1.1.1.2 christos <td>Denotes the signal strength (should be < 05.00)</td> 165 1.1.1.2 christos </tr><tr> 166 1.1.1.2 christos <td class="ttf">V</td> 167 1.1.1.2 christos <td>GPS sync status<br> 168 1.1.1.2 christos '0' => INVALID time,<br> 169 1.1.1.2 christos '1' => accuracy of +/- 20ms,<br> 170 1.1.1.2 christos '2' => accuracy of +/- 100ns</td> 171 1.1.1.2 christos </tr><tr> 172 1.1.1.2 christos <td class="ttf">CS</td> 173 1.1.1.2 christos <td> Checksum</td> 174 1.1.1.2 christos </tr><tr> 175 1.1.1.2 christos <td class="ttf"><cr><lf></td> 176 1.1.1.2 christos <td>Sentence terminator.</td> 177 1.1.1.2 christos </tr> 178 1.1.1.2 christos </tbody></table></p> 179 1.1.1.2 christos 180 1.1.1.2 christos 181 1.1.1.2 christos <h4>The 'mode' byte</h4> 182 1.1.1.2 christos 183 1.1.1.2 christos <p> 184 1.1.1.2 christos Specific GPS sentences and bitrates may be selected by setting bits of 185 1.1.1.2 christos the 'mode' in the server configuration line:<br> <tt>server 186 1.1.1.2 christos 127.127.20.x mode X</tt> 187 1.1.1.2 christos </p> 188 1.1.1.2 christos 189 1.1.1.2 christos <table border="1"> 190 1.1.1.2 christos <caption>mode byte bits and bit groups</caption> 191 1.1.1.2 christos <tbody><tr> 192 1.1.1.2 christos <th align="center">Bit</th> 193 1.1.1.2 christos <th align="center">Dec.</th> 194 1.1.1.2 christos <th align="left">Meaning</th> 195 1.1.1.2 christos </tr> 196 1.1.1.2 christos 197 1.1.1.2 christos <tr> 198 1.1.1.2 christos <td align="center">0</td> 199 1.1.1.2 christos <td align="center">1</td> 200 1.1.1.2 christos <td>process <tt>$GPMRC</tt></td> 201 1.1.1.2 christos </tr><tr> 202 1.1.1.2 christos <td align="center">1</td> 203 1.1.1.2 christos <td align="center">2</td> 204 1.1.1.2 christos <td>process <tt>$GPGGA</tt></td> 205 1.1.1.2 christos </tr><tr> 206 1.1.1.2 christos <td align="center">2</td> 207 1.1.1.2 christos <td align="center">4</td> 208 1.1.1.2 christos <td>process <tt>$GPGLL</tt></td> 209 1.1.1.2 christos </tr><tr> 210 1.1.1.2 christos <td align="center">3</td> 211 1.1.1.2 christos <td align="center">8</td> 212 1.1.1.2 christos <td>process <tt>$GPZDA</tt> or <tt>$GPZDG</tt></td> 213 1.1.1.2 christos </tr><tr> 214 1.1.1.2 christos <td rowspan="6" align="center">4-6</td> 215 1.1.1.2 christos <td align="center">0</td> 216 1.1.1.2 christos <td>linespeed 4800 bps</td> 217 1.1.1.2 christos </tr><tr> 218 1.1.1.2 christos <td align="center">16</td> 219 1.1.1.2 christos <td>linespeed 9600 bps</td> 220 1.1.1.2 christos </tr><tr> 221 1.1.1.2 christos <td align="center">32</td> 222 1.1.1.2 christos <td>linespeed 19200 bps</td> 223 1.1.1.2 christos </tr><tr> 224 1.1.1.2 christos <td align="center">48</td> 225 1.1.1.2 christos <td>linespeed 38400 bps</td> 226 1.1.1.2 christos </tr><tr> 227 1.1.1.2 christos <td align="center">64</td> 228 1.1.1.2 christos <td>linespeed 57600 bps</td> 229 1.1.1.2 christos </tr><tr> 230 1.1.1.2 christos <td align="center">80</td> 231 1.1.1.2 christos <td>linespeed 115200 bps</td> 232 1.1.1.2 christos </tr><tr> 233 1.1.1.2 christos <td align="center">7</td> 234 1.1.1.2 christos <td align="center">128</td> 235 1.1.1.2 christos <td>Write the sub-second fraction of the receive time stamp to the 236 1.1.1.2 christos clockstat file for all recognised NMEA sentences. This can be used to 237 1.1.1.2 christos get a useful value for fudge time2.<br><strong>Caveat:</strong> This 238 1.1.1.2 christos will fill your clockstat file rather fast. Use it only temporarily to 239 1.1.1.2 christos get the numbers for the NMEA sentence of your choice.</td> 240 1.1.1.2 christos </tr> 241 1.1.1.2 christos </tbody></table> 242 1.1.1.2 christos 243 1.1.1.2 christos 244 1.1.1.2 christos <p> 245 1.1.1.2 christos The default (mode 0) is to process all supported sentences at a linespeed 246 1.1.1.2 christos of 4800 bps, which results in the first one received and recognised in 247 1.1.1.2 christos each cycle being used. If only specific sentences should be 248 1.1.1.2 christos recognised, then the mode byte must be chosen to enable only the selected 249 1.1.1.2 christos ones. Multiple sentences may be selected by adding their mode bit 250 1.1.1.2 christos values, but of those enabled still only the first received sentence in a 251 1.1.1.2 christos cycle will be used. Using more than one sentence per cycle is 252 1.1.1.2 christos impossible, because 253 1.1.1.2 christos </p><ul> 254 1.1.1.2 christos <li>there is only <a href="#fudgetime2">fudge time2</a> available to 255 1.1.1.2 christos compensate for transmission delays but every sentence would need a 256 1.1.1.2 christos different one and 257 1.1.1.2 christos </li><li>using more than one sentence per cycle overstuffs the internal data 258 1.1.1.2 christos filters. 259 1.1.1.2 christos </li></ul> 260 1.1.1.2 christos The driver uses 4800 bits per second by default, but faster bitrates can 261 1.1.1.2 christos be selected using bits 4 to 6 of the mode field. 262 1.1.1.2 christos <p></p> 263 1.1.1.2 christos 264 1.1.1.2 christos <p> 265 1.1.1.2 christos <strong>Caveat:</strong> Using higher line speeds does not necessarily 266 1.1.1.2 christos increase the precision of the timing device. Higher line speeds are 267 1.1.1.2 christos not necessarily helpful for the NMEA driver, either. They can be 268 1.1.1.2 christos used to accomodate for an amount of data that does not fit into a 269 1.1.1.2 christos 1-second cycle at 4800 bps, but high-speed high-volume NMEA data is likely 270 1.1.1.2 christos to cause trouble with the serial line driver since NMEA supports no 271 1.1.1.2 christos protocol handshake. Any device that is exclusively used for time 272 1.1.1.2 christos synchronisation purposes should be configured to transmit the relevant 273 1.1.1.2 christos data only, e.g. one <tt>$GPRMC</tt> or <tt>$GPZDA</tt> per second, at a 274 1.1.1.2 christos linespeed of 4800 bps or 9600 bps. 275 1.1.1.2 christos </p> 276 1.1.1.2 christos 277 1.1.1.2 christos <p> 278 1.1.1.2 christos <a href="https://support.ntp.org/bin/view/Support/ConfiguringNMEARefclocks">Configuring 279 1.1.1.2 christos NMEA Refclocks</a> might give further useful hints for specific hardware 280 1.1.1.2 christos devices that exhibit strange or curious behaviour. 281 1.1.1.2 christos </p> 282 1.1.1.2 christos 283 1.1.1.2 christos <p> 284 1.1.1.2 christos To make a specific setting, select the corresponding decimal values from 285 1.1.1.2 christos the mode byte table, add them all together and enter the resulting 286 1.1.1.2 christos decimal value into the clock configuration line. 287 1.1.1.2 christos </p> 288 1.1.1.2 christos 289 1.1.1.2 christos <h4>Setting up the Garmin GPS-25XL</h4> 290 1.1.1.2 christos 291 1.1.1.2 christos Switch off all output with by sending it the following string. 292 1.1.1.2 christos <pre>"$PGRMO,,2<cr><lf>"</pre> 293 1.1.1.2 christos <p>Now switch only $GPRMC on by sending it the following string.</p> 294 1.1.1.2 christos <pre>"$PGRMO,GPRMC,1<cr><lf>"</pre> 295 1.1.1.2 christos 296 1.1.1.2 christos <p>On some systems the PPS signal isn't switched on by default. It can be 297 1.1.1.2 christos switched on by sending the following string.</p> 298 1.1.1.2 christos <pre>"$PGRMC,,,,,,,,,,,,2<cr><lf>"</pre> 299 1.1.1.2 christos 300 1.1.1.2 christos <h4>Monitor Data</h4> 301 1.1.1.2 christos 302 1.1.1.2 christos <p>The GPS sentence that is used is written to the clockstats file and 303 1.1.1.2 christos available with ntpq -c clockvar.</p> 304 1.1.1.2 christos 305 1.1.1.2 christos <h4>Fudge Factors</h4> 306 1.1.1.2 christos 307 1.1.1.2 christos <dl> 308 1.1.1.2 christos <dt><tt>time1 <i>time</i></tt></dt> 309 1.1.1.2 christos <dd>Specifies the PPS time offset calibration factor, in seconds and fraction, with default 0.0.</dd> 310 1.1.1.2 christos <dt><a name="fudgetime2"><tt>time2 <i>time</i></tt></a></dt> 311 1.1.1.2 christos <dd>Specifies the serial end of line time offset calibration factor, in seconds and fraction, with default 312 1.1.1.2 christos 0.0.</dd> 313 1.1.1.2 christos <dt><tt>stratum <i>number</i></tt></dt> 314 1.1.1.2 christos <dd>Specifies the driver stratum, in decimal from 0 to 15, with default 0.</dd> 315 1.1.1.2 christos <dt><tt>refid <i>string</i></tt></dt> 316 1.1.1.2 christos <dd>Specifies the driver reference identifier, an ASCII string from one to four characters, with 317 1.1.1.2 christos default <tt>GPS</tt>.</dd> 318 1.1.1.2 christos <dt><tt>flag1 0 | 1</tt></dt> 319 1.1.1.2 christos <dd>Disable PPS signal processing if 0 (default); enable PPS signal processing if 1.</dd> 320 1.1.1.2 christos <dt><tt>flag2 0 | 1</tt></dt> 321 1.1.1.2 christos <dd>If PPS signal processing is enabled, capture the pulse on the rising edge if 0 (default); capture on the 322 1.1.1.2 christos falling edge if 1.</dd> 323 1.1.1.2 christos <dt><tt>flag3 0 | 1</tt></dt> 324 1.1.1.2 christos <dd>If PPS signal processing is enabled, use the <tt>ntpd</tt> clock discipline if 0 (default); use the kernel 325 1.1.1.2 christos discipline if 1.</dd> 326 1.1.1.2 christos <dt><tt>flag4 0 | 1</tt></dt> 327 1.1.1.2 christos <dd>Obscures location in timecode: 0 for disable (default), 1 for enable.</dd> 328 1.1.1.2 christos </dl> 329 1.1.1.2 christos 330 1.1.1.2 christos <p>Additional Information</p> 331 1.1.1.2 christos <p><a href="../refclock.html">Reference Clock Drivers</a></p> 332 1.1.1.2 christos <hr> 333 1.1.1.2 christos <script type="text/javascript" language="javascript" src="scripts/footer.txt"></script> 334 1.1.1.2 christos </body></html> 335
Indexes created Mon Oct 26 00:26:21 UTC 2026