151 lines
4.7 KiB
HTML
151 lines
4.7 KiB
HTML
<HTML>
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<HEAD>
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<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
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<META NAME="GENERATOR" CONTENT="Mozilla/4.01 [en] (Win95; I) [Netscape]">
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<TITLE>Arbiter 1088A/B GPS Receiver
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</TITLE>
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</HEAD>
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<BODY>
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<H3>
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Arbiter 1088A/B GPS Receiver</H3>
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<HR>
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<H4>
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Synopsis</H4>
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Address: 127.127.11.<I>u</I>
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<BR>Reference ID: <TT>GPS</TT>
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<BR>Driver ID: <TT>GPS_ARBITER</TT>
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<BR>Serial Port: <TT>/dev/gps<I>u</I></TT>; 9600 baud, 8-bits, no parity
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<BR>Features: <TT>tty_clk</TT>
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<H4>
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Description</H4>
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This driver supports the Arbiter 1088A/B Satellite Controlled Clock. The
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claimed accuracy of this clock is 100 ns relative to the PPS output when
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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 savings
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time feature should be disables (<TT>D0</TT> command) and the broadcast
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mode set to operate in UTC (<TT>BU</TT> command).
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<P>The timecode format supported by this driver is selected by the poll
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sequence <TT>B5</TT>, which initiates a line in the following format to
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be repeated once per second until turned off by the <TT>B0</TT> command.
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<P>Format <TT>B5</TT> (24 ASCII printing characters):
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<PRE><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</PRE>
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The alarm condition is indicated by a '?' at i, which indicates the receiver
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is not synchronized. In normal operation, a line consisting of the timecode
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followed by the time quality character (TQ) followed by the receiver status
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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 <TT>TQ</TT> (IEEE P1344 estimated worst-case time quality)
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<PRE>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</PRE>
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The status string is encoded as follows:
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<P>Format <TT>SR</TT> (25 ASCII printing characters)
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<PRE>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</PRE>
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A three-stage median filter is used to reduce jitter and provide a dispersion
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measure. The driver makes no attempt to correct for the intrinsic jitter
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of the radio itself.
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<H4>
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Monitor Data</H4>
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When enabled by the <TT>flag4</TT> fudge flag, an additional line containing
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the latitude, longitude, elevation and optional deviation data is written
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to the <TT>clockstats</TT> file. The deviation data operates with an external
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pulse-per-second (PPS) input, such as a cesium oscillator or another radio
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clock. The PPS input should be connected to the B event channel and the
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radio initialized for deviation data on that channel. The deviation data
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consists of the mean offset and standard deviation of the external PPS
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signal relative the GPS signal, both in microseconds over the last 16 seconds.
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<H4>
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Fudge Factors</H4>
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<DL>
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<DT>
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<TT>time1 <I>time</I></TT></DT>
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<DD>
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Specifies the time offset calibration factor, in seconds and fraction,
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with default 0.0.</DD>
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<DT>
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<TT>time2 <I>time</I></TT></DT>
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<DD>
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Not used by this driver.</DD>
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<DT>
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<TT>stratum <I>number</I></TT></DT>
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<DD>
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Specifies the driver stratum, in decimal from 0 to 15, with default 0.</DD>
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<DT>
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<TT>refid <I>string</I></TT></DT>
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<DD>
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Specifies the driver reference identifier, an ASCII string from one to
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four characters, with default <TT>GPS</TT>.</DD>
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<DT>
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<TT>flag1 0 | 1</TT></DT>
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<DD>
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Not used by this driver.</DD>
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<DT>
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<TT>flag2 0 | 1</TT></DT>
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<DD>
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Not used by this driver.</DD>
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<DT>
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<TT>flag3 0 | 1</TT></DT>
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<DD>
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Not used by this driver.</DD>
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<DT>
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<TT>flag4 0 | 1</TT></DT>
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<DD>
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Enable verbose <TT>clockstats</TT> recording if set.</DD>
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</DL>
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Additional Information
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<P><A HREF="refclock.htm">Reference Clock Drivers</A>
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<HR>
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<ADDRESS>
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David L. Mills (mills@udel.edu)</ADDRESS>
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</BODY>
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</HTML>
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