19c2daa00SOllivier Robert<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 29c2daa00SOllivier Robert<html> 39c2daa00SOllivier Robert<head> 4ea906c41SOllivier Robert<meta http-equiv="content-type" content="text/html;charset=iso-8859-1"> 59c2daa00SOllivier Robert<meta name="generator" content="HTML Tidy, see www.w3.org"> 62b15cb3dSCy Schubert<title>Reference Clock Support</title> 79c2daa00SOllivier Robert<link href="scripts/style.css" type="text/css" rel="stylesheet"> 89c2daa00SOllivier Robert</head> 99c2daa00SOllivier Robert<body> 102b15cb3dSCy Schubert<h3>Reference Clock Support</h3> 119c2daa00SOllivier Robert<img src="pic/stack1a.jpg" alt="gif" align="left">Master Time Facility at the <a href="http://www.eecis.udel.edu/%7emills/lab.html">UDel Internet Research Laboratory</a> 122b15cb3dSCy Schubert<p>Last update: 132b15cb3dSCy Schubert <!-- #BeginDate format:En2m -->10-Mar-2014 05:20<!-- #EndDate --> 142b15cb3dSCy Schubert UTC</p> 159c2daa00SOllivier Robert<br clear="left"> 169c2daa00SOllivier Robert<h4>Related Links</h4> 172b15cb3dSCy Schubert<script type="text/javascript" language="javascript" src="scripts/hand.txt"></script> 182b15cb3dSCy Schubert<script type="text/javascript" language="javascript" src="scripts/refclock.txt"></script> 192b15cb3dSCy Schubert<script type="text/javascript" language="javascript" src="scripts/audio.txt"></script> 209c2daa00SOllivier Robert<h4>Table of Contents</h4> 219c2daa00SOllivier Robert<ul> 222b15cb3dSCy Schubert <li class="inline"><a href="#intro">Introduction</a></li> 232b15cb3dSCy Schubert <li class="inline"><a href="#spec">Special Considerations</a></li> 242b15cb3dSCy Schubert <li class="inline"><a href="#list">List of Reference Clock Drivers</a></li> 259c2daa00SOllivier Robert</ul> 269c2daa00SOllivier Robert<hr> 272b15cb3dSCy Schubert<h4 id="intro">Introduction</h4> 282b15cb3dSCy Schubert<p>NTP Version 4 supports almost four dozen satellite, radio and telephone modem reference clocks plus several audio devices for instrumentation signals. A general description of the reference clock support is on this page. Additional information about each reference clock driver can be found via links from this page. Additional information is on the <a href="rdebug.html">Debugging Hints for Reference Clock Drivers</a> and <a href="howto.html">How To Write a Reference Clock Driver</a> pages. Information on how to support pulse-per-second (PPS) signals produced by some devices is on the <a href="pps.html">Pulse-per-second (PPS) Signal Interfacing</a> page. All reference clock drivers require that the reference clock use only Coordinated Universal Time (UTC). Timezone and standard/daylight adjustments are performed by the operating system kernel.</p> 292b15cb3dSCy Schubert<p>A reference clock will generally (though not always) be a radio timecode receiver synchronized to standard time as provided by NIST and USNO in the US, NRC in Canada and their counterparts elsewhere in the world. A device driver specific to each reference clock must be compiled in the distribution; however, most common radio, satellite and telephone modem clocks are included by default and are activated by configuration commands.</p> 302b15cb3dSCy Schubert<p>Reference clocks are supported in the same way as ordinary NTP clients and use the same filter, select, cluster and combine algorithms. Drivers have addresses in the form 127.127.<i>t.u</i>, where <i>t</i> is the driver type and <i>u</i> is a unit number in the range 0-3 to distinguish multiple instances of the same driver. The connection to the computer is device dependent, usually a serial port, parallel port or special bus peripheral, but some can work directly from an audio codec or sound card. The particular device is specified by adding a soft link from the name used by the driver to the particular device name.</p> 31*276da39aSCy Schubert<p>The <tt>server</tt> command is used to configure a reference clock. Only the <tt>mode</tt>, <tt>minpoll</tt>, <tt>maxpoll</tt>, and <tt>prefer</tt> options are supported for reference clocks, as described on the <a href="clockopt.html">Reference Clock Commands</a> page. The <tt>prefer</tt> option is discussed on the <a href="prefer.html">Mitigation Rules and the <tt>prefer</tt> Keyword</a> page. Some of these options have meaning only for selected clock drivers.</p> 322b15cb3dSCy Schubert<p>The <tt>fudge</tt> command can be used to provide additional information for individual drivers and normally follows immediately after the <tt>server</tt> command. The reference clock stratum is by default 0, so that the server stratum appears to clients as 1. The <tt>stratum</tt> option can be used to set the stratum to any value in the range 0 through 15. The <tt>refid</tt> option can be used to change the reference identifier, as might in the case when the driver is disciplined by a pulse-per-second (PPS) source. The device-dependent <tt>mode</tt>, <tt>time</tt> and <tt>flag</tt> options can provide additional driver customization.</p> 332b15cb3dSCy Schubert<h4 id="spec">Special Considerations</h4> 342b15cb3dSCy Schubert<p>The <a href="audio.html">Audio Drivers</a> page describes three software drivers that process audio signals from an audio codec or sound card. One is for the NIST time and frequency stations WWV and WWVH, another for the Canadian time and frequency station CHU. These require an external shortwave radio and antenna. A third is for the generic IRIG signal produced by some timing devices. Currently, these are supported in FreeBSD, Solaris and SunOS and likely in other system as well.</p> 352b15cb3dSCy Schubert<p>The <a href="drivers/driver1.html"> Undisciplined Local Clock</a> driver can simulate a reference clock when no external synchronization sources are available. If a server with this driver is connected directly or indirectly to the public Internet, there is some danger that it can destabilize other clients. It is not recommended that the local clock driver be used in this way, as the orphan mode described on the <a href="assoc.html">Association Management</a> page provides a generic backup capability.</p> 362b15cb3dSCy Schubert<p>The local clock driver can also be used when an external synchronization source such as the IEEE 1588 Precision Time Protocol or NIST Lockclock directly synchronizes the computer time. Further information is on the <a href="extern.html">External Clock Discipline and the Local Clock Driver</a> page.</p> 372b15cb3dSCy Schubert<p>Several drivers make use of the pulse-per-second (PPS) signal discipline, which is part of the generic driver interface, so require no specific configuration. For those drivers that do not use this interface, the <a href="drivers/driver22.html"> PPS Clock Discipline</a> driver can be can provide this function. It normally works in conjunction with the reference clock that produces the timecode signal, but can work with another driver or remote server. When PPS kernel features are present, the driver can redirect the PPS signal to the kernel.</p> 382b15cb3dSCy Schubert<p>Some drivers depending on longwave or shortwave radio services need to know the radio propagation time from the transmitter to the receiver. This must be calculated for each specific receiver location and requires the geographic coordinates of both the transmitter and receiver. The transmitter coordinates for various radio services are given in the <a href="http://www.eecis.udel.edu/%7emills/ntp/qth.html">Time and Frequency Standard Station Information</a> page. Receiver coordinates can be obtained locally or from Google Earth. The actual calculations are beyond the scope of this document.</p> 392b15cb3dSCy Schubert<p>Depending on interface type, port speed, etc., a reference clock can have a small residual offset relative to another. To reduce the effects of jitter when switching from one driver to the another, it is useful to calibrate the drivers to a common ensemble offset. The <tt>enable calibrate</tt> configuration command described on the <a href="miscopt.html">Miscellaneous Options</a> page activates a special feature which automatically calculates a correction factor for each driver relative to an association designated the prefer peer.</p> 402b15cb3dSCy Schubert<h4 id="list"> List of Reference Clock Drivers</h4> 412b15cb3dSCy Schubert<p>Following is a list showing the type and title of each driver currently implemented. The compile-time identifier for each is shown in parentheses. Click on a selected type for specific description and configuration documentation, including the clock address, reference ID, driver ID, device name and serial line speed. For those drivers without specific documentation, please contact the author listed in the <a href="copyright.html">Copyright Notice</a> page.</p> 429c2daa00SOllivier Robert<ul> 432b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver1.html">Type 1</a> Undisciplined Local Clock (<tt>LOCAL</tt>)</li> 442b15cb3dSCy Schubert <li class="inline">Type 2 Deprecated: was Trak 8820 GPS Receiver</li> 452b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver3.html">Type 3</a> PSTI/Traconex 1020 WWV/WWVH Receiver (<tt>WWV_PST</tt>)</li> 462b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver4.html">Type 4</a> Spectracom WWVB/GPS Receivers (<tt>WWVB_SPEC</tt>)</li> 472b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver5.html">Type 5</a> TrueTime GPS/GOES/OMEGA Receivers (<tt>TRUETIME</tt>)</li> 482b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver6.html">Type 6</a> IRIG Audio Decoder (<tt>IRIG_AUDIO</tt>)</li> 492b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver7.html">Type 7</a> Radio CHU Audio Demodulator/Decoder (<tt>CHU</tt>)</li> 502b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver8.html">Type 8</a> Generic Reference Driver (<tt>PARSE</tt>)</li> 512b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver9.html">Type 9</a> Magnavox MX4200 GPS Receiver (<tt>GPS_MX4200</tt>)</li> 522b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver10.html">Type 10</a> Austron 2200A/2201A GPS Receivers (<tt>GPS_AS2201</tt>)</li> 532b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver11.html">Type 11</a> Arbiter 1088A/B GPS Receiver (<tt>GPS_ARBITER</tt>)</li> 542b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver12.html">Type 12</a> KSI/Odetics TPRO/S IRIG Interface (<tt>IRIG_TPRO</tt>)</li> 552b15cb3dSCy Schubert <li class="inline">Type 13 Leitch CSD 5300 Master Clock Controller (<tt>ATOM_LEITCH</tt>)</li> 562b15cb3dSCy Schubert <li class="inline">Type 14 EES M201 MSF Receiver (<tt>MSF_EES</tt>)</li> 572b15cb3dSCy Schubert <li class="inline">Type 15 reserved</li> 582b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver16.html">Type 16</a> Bancomm GPS/IRIG Receiver (<tt>GPS_BANCOMM</tt>)</li> 592b15cb3dSCy Schubert <li class="inline">Type 17 Datum Precision Time System (<tt>GPS_DATUM</tt>)</li> 602b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver18.html">Type 18</a> NIST/USNO/PTB Modem Time Services (<tt>ACTS_MODEM</tt>)</li> 612b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver19.html">Type 19</a> Heath WWV/WWVH Receiver (<tt>WWV_HEATH</tt>)</li> 622b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver20.html">Type 20</a> Generic NMEA GPS Receiver (<tt>NMEA</tt>)</li> 632b15cb3dSCy Schubert <li class="inline">Type 21 TrueTime GPS-VME Interface (<tt>GPS_VME</tt>)</li> 642b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver22.html">Type 22</a> PPS Clock Discipline (<tt>PPS</tt>)</li> 652b15cb3dSCy Schubert <li class="inline">Type 23 reserved</li> 662b15cb3dSCy Schubert <li class="inline">Type 24 reserved</li> 672b15cb3dSCy Schubert <li class="inline">Type 25 reserved</li> 682b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver26.html">Type 26</a> Hewlett Packard 58503A GPS Receiver (<tt>GPS_HP</tt>)</li> 692b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver27.html">Type 27</a> Arcron MSF Receiver (<tt>MSF_ARCRON</tt>)</li> 702b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver28.html">Type 28</a> Shared Memory Driver (<tt>SHM</tt>)</li> 712b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver29.html">Type 29</a> Trimble Navigation Palisade GPS (<tt>GPS_PALISADE</tt>)</li> 722b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver30.html">Type 30</a> Motorola UT Oncore GPS <tt>GPS_ONCORE</tt>)</li> 732b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver31.html">Type 31</a> Rockwell Jupiter GPS (<tt>GPS_JUPITER</tt>)</li> 742b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver32.html">Type 32</a> Chrono-log K-series WWVB receiver (<tt>CHRONOLOG</tt>)</li> 752b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver33.html">Type 33</a> Dumb Clock (<tt>DUMBCLOCK</tt>)</li> 762b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver34.html">Type 34</a> Ultralink WWVB Receivers (<tt>ULINK</tt>)</li> 772b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver35.html">Type 35</a> Conrad Parallel Port Radio Clock (<tt>PCF</tt>)</li> 782b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver36.html">Type 36</a> Radio WWV/H Audio Demodulator/Decoder (<tt>WWV</tt>)</li> 792b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver37.html">Type 37</a> Forum Graphic GPS Dating station (<tt>FG</tt>)</li> 802b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver38.html">Type 38</a> hopf GPS/DCF77 6021/komp for Serial Line (<tt>HOPF_S</tt>)</li> 812b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver39.html">Type 39</a> hopf GPS/DCF77 6039 for PCI-Bus (<tt>HOPF_P</tt>)</li> 822b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver40.html">Type 40</a> JJY Receivers (<tt>JJY</tt>)</li> 832b15cb3dSCy Schubert <li class="inline">Type 41 TrueTime 560 IRIG-B Decoder</li> 842b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver42.html">Type 42</a> Zyfer GPStarplus Receiver</li> 852b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver43.html">Type 43</a> RIPE NCC interface for Trimble Palisade</li> 862b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver44.html">Type 44</a> NeoClock4X - DCF77 / TDF serial line</li> 872b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver45.html">Type 45</a> Spectracom TSYNC PCI</li> 882b15cb3dSCy Schubert <li class="inline"><a href="drivers/driver46.html">Type 46</a> GPSD NG client protocol</li> 899c2daa00SOllivier Robert</ul> 909c2daa00SOllivier Robert<hr> 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