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