![]() The reference clock stratum is by default 0, so that the server stratum appears to clients as 1. The fudge command can be used to provide additional information for individual drivers and normally follows immediately after the server command. Some of these options have meaning only for selected clock drivers. The prefer option is discussed on the Mitigation Rules and the prefer Keyword page. Only the mode, minpoll, maxpoll, and prefer options are supported for reference clocks, as described on the Reference Clock Commands page. The server command is used to configure a reference clock. The particular device is specified by adding a soft link from the name used by the driver to the particular device name. 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. t.u, where t is the driver type and u is a unit number in the range 0-3 to distinguish multiple instances of the same driver. Drivers have addresses in the form 127.127. ![]() ![]() Reference clocks are supported in the same way as ordinary NTP clients and use the same filter, select, cluster and combine algorithms. 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. Timezone and standard/daylight adjustments are performed by the operating system kernel.Ī 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. All reference clock drivers require that the reference clock use only Coordinated Universal Time (UTC). Information on how to support pulse-per-second (PPS) signals produced by some devices is on the Pulse-per-second (PPS) Signal Interfacing page. Additional information is on the Debugging Hints for Reference Clock Drivers and How To Write a Reference Clock Driver pages. Additional information about each reference clock driver can be found via links from this page. A general description of the reference clock support is on this page. ![]() NTP Version 4 supports almost four dozen satellite, radio and telephone modem reference clocks plus several audio devices for instrumentation signals. Reference Clock Support Reference Clock Support Master Time Facility at the UDel Internet Research Laboratory ![]()
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