160 lines
5.6 KiB
HTML
160 lines
5.6 KiB
HTML
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<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>TrueTime GPS/GOES/OMEGA Receivers
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</TITLE>
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</HEAD>
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<BODY>
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<H3>
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TrueTime GPS/GOES/OMEGA Receivers</H3>
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<HR>
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<H4>
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Synopsis</H4>
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Address: 127.127.5.<I>u</I>
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<BR>Reference ID: <TT>GPS, OMEGA, GOES</TT>
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<BR>Driver ID: <TT>TRUETIME</TT>
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<BR>Serial Port: <TT>/dev/true<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 several models models of Kinemetrics/TrueTime timing
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receivers, including 468-DC MK III GOES Synchronized Clock, GPS- DC MK
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III and GPS/TM-TMD GPS Synchronized Clock, XL-DC (a 151-602-210, reported
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by the driver as a GPS/TM-TMD), GPS-800 TCU (an 805-957 with the RS232
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Talker/Listener module), OM-DC OMEGA Synchronized Clock, and very likely
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others in the same model family that use the same timecode formats.
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<P>Most of this code is originally from refclock_wwvb.c with thanks. It
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has been so mangled that wwvb is not a recognizable ancestor.
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<PRE>Timcode format: ADDD:HH:MM:SSQCL
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A - control A (this is stripped before we see it)
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Q - Quality indication (see below)
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C - Carriage return
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L - Line feed
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Quality codes indicate possible error of
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468-DC GOES Receiver:
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GPS-TM/TMD Receiver:
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? +/- 500 milliseconds # +/- 50 milliseconds
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* +/- 5 milliseconds . +/- 1 millisecond
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space less than 1 millisecond
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OM-DC OMEGA Receiver:
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> +/- 5 seconds
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? +/- 500 milliseconds # +/- 50 milliseconds
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* +/- 5 milliseconds . +/- 1 millisecond
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A-H less than 1 millisecond. Character indicates which
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station
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is being received as follows: A = Norway, B = Liberia,
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C = Hawaii, D = North Dakota, E = La Reunion, F =
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Argentina,
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G = Australia, H = Japan.</PRE>
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The carriage return start bit begins on 0 seconds and extends to 1 bit
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time.
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<P>Notes on 468-DC and OMEGA receiver:
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<P>Send the clock a <TT>R</TT> or <TT>C</TT> and once per second a timestamp
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will appear. Send a <TT>R</TT> to get the satellite position once (GOES
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only).
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<P>Notes on the 468-DC receiver:
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<P>Since the old east/west satellite locations are only historical, you
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can't set your clock propagation delay settings correctly and still use
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automatic mode. The manual says to use a compromise when setting the switches.
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This results in significant errors. The solution; use fudge time1 and time2
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to incorporate corrections. If your clock is set for 50 and it should be
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58 for using the west and 46 for using the east, use the line
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<P><TT>fudge 127.127.5.0 time1 +0.008 time2 -0.004</TT>
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<P>This corrects the 4 milliseconds advance and 8 milliseconds retard needed.
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The software will ask the clock which satellite it sees.
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<P>The PCL720 from PC Labs has an Intel 8253 look-alike, as well as a bunch
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of TTL input and output pins, all brought out to the back panel. If you
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wire a PPS signal (such as the TTL PPS coming out of a GOES or other Kinemetrics/Truetime
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clock) to the 8253's GATE0, and then also wire the 8253's OUT0 to the PCL720's
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INPUT3.BIT0, then we can read CTR0 to get the number of microseconds since
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the last PPS upward edge, mediated by reading OUT0 to find out if the counter
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has wrapped around (this happens if more than 65535us (65ms) elapses between
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the PPS event and our being called.)
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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, every received timecode
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is written as-is to the <TT>clockstats</TT> file.
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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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to be used for the West satellite, 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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. Specifies the time offset calibration factor, in seconds and fraction,
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to be used for the East satellite, with default 0.0.</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>TRUE</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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Silence the clock side of ntpd, just reading the clock without trying to
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write to it.</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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Generate a debug file /tmp/true%d.</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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Not used by this driver.</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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