141 lines
4.6 KiB
HTML
141 lines
4.6 KiB
HTML
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<!-- $NetBSD: driver11.html,v 1.1 1998/12/30 20:20:34 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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Arbiter 1088A/B GPS Receiver
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</title></head><body><h3>
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Arbiter 1088A/B GPS Receiver
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</h3><hr>
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<p><h4>Synopsis</h4>
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<p>Address: 127.127.11.<var>u</var>
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<br>Reference ID: GPS
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<br>Driver ID: GPS_ARBITER
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<br>Serial Port: <code>/dev/gps<var>u</var></code>; 9600 baud, 8-bits,
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no parity
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<br>Features: <code>tty_clk</code>
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<p><h4>Description</h4>
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<p>This driver supports the Arbiter 1088A/B Satellite Controlled Clock.
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The claimed accuracy of this clock is 100 ns relative to the PPS output
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when receiving four or more satellites.
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<p>The receiver should be configured before starting the NTP daemon, in
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order to establish reliable position and operating conditions. It does
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not initiate surveying or hold mode. For use with NTP, the daylight
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savings time feature should be disables (<code>D0</code> command) and
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the broadcast mode set to operate in UTC (<code>BU</code> command).
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<p>The timecode format supported by this driver is selected by the poll
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sequence <code>B5</code>, which initiates a line in the following format
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to be repeated once per second until turned off by the <code>B0</code>
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command.
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<p>Format <code>B5</code> (24 ASCII printing characters):
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<pre>
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<cr><lf>i yy ddd hh:mm:ss.000bbb
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on-time = <cr>
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i = synchronization flag (' ' = locked, '?' = unlocked)
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yy = year of century
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ddd = day of year
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hh:mm:ss = hours, minutes, seconds
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.000 = fraction of second (not used)
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bbb = tailing spaces for fill
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</pre>
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<p>The alarm condition is indicated by a '?' at i, which indicates the
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receiver is not synchronized. In normal operation, a line consisting of
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the timecode followed by the time quality character (TQ) followed by the
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receiver status string (SR) is written to the clockstats file.
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<p>The time quality character is encoded in IEEE P1344 standard:
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<p>Format <code>TQ</code> (IEEE P1344 estimated worst-case time quality)
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<pre>
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0 clock locked, maximum accuracy
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F clock failure, time not reliable
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4 clock unlocked, accuracy < 1 us
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5 clock unlocked, accuracy < 10 us
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6 clock unlocked, accuracy < 100 us
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7 clock unlocked, accuracy < 1 ms
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8 clock unlocked, accuracy < 10 ms
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9 clock unlocked, accuracy < 100 ms
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A clock unlocked, accuracy < 1 s
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B clock unlocked, accuracy < 10 s
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</pre>
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<p>The status string is encoded as follows:
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<p>Format <code>SR</code> (25 ASCII printing characters)
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<pre>
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V=vv S=ss T=t P=pdop E=ee
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vv = satellites visible
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ss = relative signal strength
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t = satellites tracked
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pdop = position dilution of precision (meters)
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ee = hardware errors
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</pre>
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<p>A three-stage median filter is used to reduce jitter and provide a
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dispersion measure. The driver makes no attempt to correct for the
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intrinsic jitter of the radio itself.
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<p><h4>Monitor Data</h4>
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<p>The driver writes each timecode as received to the
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<code>clockstats</code> file. When enabled by the <code>flag4</code>
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fudge flag, an additional line containing the latitude, longitude,
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elevation and optional deviation data is written to the
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<code>clockstats</code> file. The deviation data operates with an
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external pulse-per-second (PPS) input, such as a cesium oscillator or
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another radio clock. The PPS input should be connected to the B event
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channel and the radio initialized for deviation data on that channel.
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The deviation data consists of the mean offset and standard deviation of
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the external PPS signal relative the GPS signal, both in microseconds
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over the last 16 seconds.
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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. For a calibrated Sun IPC, the correct value
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is about .0065.
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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>GPS</code>.
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<p><dt><code>flag1 0 | 1</code>
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<dd>Not used by this driver.
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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 extended <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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