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diff --git a/html/refclock.html b/html/refclock.html index d8969e38cbc3b..46d4908fd8d52 100644 --- a/html/refclock.html +++ b/html/refclock.html @@ -28,7 +28,7 @@ <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> <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> <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> -<p>The <tt>server</tt> command is used to configure a reference clock. Only the <tt>mode>,<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> +<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> <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> <h4 id="spec">Special Considerations</h4> <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> |