99 lines
3.6 KiB
HTML
99 lines
3.6 KiB
HTML
<!-- $NetBSD: driver7.html,v 1.1 1998/12/30 20:20:35 mcr Exp $ -->
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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML Strict//EN">
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<html><head><title>
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Scratchbuilt CHU Receiver
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</title></head><body><h3>
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Scratchbuilt CHU Receiver
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</h3><hr>
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<p><h4>Synopsis</h4>
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<p>Address: 127.127.7.<var>u</var>
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<br>Reference ID: CHU
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<br>Driver ID: CHU
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<br>Serial Port: <code>/dev/chu<var>u</var></code>; 300 baud, 8-bits, no
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parity
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<br>Features: <code>chu_clk</code>
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<p><h4>Description</h4>
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<p>This driver supports a shortwave receiver and special modem circuitry
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described in the ./gadget directory of the xntp3 distribution. It
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requires the <code>chu_clk</code> line discipline or streams module
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described in the <a href="ldisc.html">Line Disciplines and Streams
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Drivers</a> page. It also requires a gadget box and 300-bps modem, such
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as described in the <a href="pps.html">Pulse-per-second (PPS) Signal
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Interfacing</a> page.
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<p>Unlike the NIST time services, whose timecode requires quite
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specialized hardware to interpret, the CHU timecode can be received
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directly via a serial port after demodulation. While there are currently
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no known commercial CHU receivers, the hardware required to receive the
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CHU timecode is fairly simple to build. While it is possible to
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configure several CHU units simultaneously, this is in general not
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useful.
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<p>The <code>time1</code> fudge option can be used to set the CHU
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propagation delay, compensate for inherent latencies in the serial port
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hardware and operating system. The default value is 0.0025 seconds,
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which is about right for Toronto. Values for other locations can be
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calculated using the propdelay program in the util directory of the
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xntp3 distribution or equivalent means.
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<p>The <code>time2</code> fudge option can also be used to compensate
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for inherent latencies in the serial port hardware and operating system.
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The value, which defaults to zero, is in addition to the propagation
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delay provided by the time1 option. The default value is 0.0002 seconds,
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which is about right for typical telephone modem chips.
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<p>The <code>flag1</code> option can be used to modify the averaging
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algorithm used to smooth the clock indications. Ordinarily, the
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algorithm picks the median of a set of samples, which is appropriate
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under conditions of poor to fair radio propagation conditions. If the
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clock is located relatively close to the WWV or WWVH transmitters,
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setting this flag will cause the algorithm to average the set of
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samples, which can reduce the residual jitter and improve accuracy.
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<p><h4>Monitor Data</h4>
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<p>When enabled by the <code>flag4</code> fudge flag, every received
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timecode is written as-is to the <code>clockstats</code> file.
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<p><h4>Fudge Factors</h4>
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<dl>
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<dt><code>time1 <i>time</i></code>
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<dd>Specifies the time offset calibration factor, in seconds and
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fraction, with default 0.0.
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<p><dt><code>time2 <i>time</i></code>
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<dd>Not used by this driver.
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<p><dt><code>stratum <i>number</i></code>
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<dd>Specifies the driver stratum, in decimal from 0 to 15, with default
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0.
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<p><dt><code>refid <i>string</i></code>
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<dd>Specifies the driver reference identifier, an ASCII string from one
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to four characters, with default <code>CHU</code>.
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<p><dt><code>flag1 0 | 1</code>
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<dd>See above.
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<p><dt><code>flag2 0 | 1</code>
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<dd>Not used by this driver.
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<p><dt><code>flag3 0 | 1</code>
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<dd>Enable <code>ppsclock</code> line discipline/streams module if set.
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<p><dt><code>flag4 0 | 1</code>
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<dd>Enable <code>clockstats</code> recording if set.
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</dl>
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<p>Additional Information
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<p><a href="refclock.html"> Reference Clock Drivers</a>
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<hr><address>David L. Mills (mills@udel.edu)</address></body></html>
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