191 lines
5.6 KiB
HTML
191 lines
5.6 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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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-
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1">
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<META NAME="GENERATOR" CONTENT="Mozilla/4.06 [en] (X11; I; FreeBSD
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3.0-CURRENT i386) [Netscape]">
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<TITLE>Motorola Oncore 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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Motorola Oncore GPS receiver</H3>
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<HR>
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<H4>
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Synopsis</H4>
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Address: 127.127.30.<i>u</i><BR>
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Reference ID: <TT>GPS</TT><BR>
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Driver ID: ONCORE<BR>
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Serial Port: <TT>/dev/oncore.serial.</TT><i>u</i>; 9600 baud, 8-bits,
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no parity.<BR>
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PPS Port: <TT>/dev/oncore.pps.</TT><i>u</i>; <TT>PPS_CAPTUREASSERT</TT>
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required, <TT>PPS_OFFSETASSERT</TT> supported.<BR>
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Configuration File: <TT>/etc/ntp.oncore<TT><i>u</i> or,
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<TT>/etc/ntp.oncore.<TT><i>u</i>, or <TT>/etc/ntp.oncore<TT>.
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<H4>
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Description</H4>
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This driver supports most models of the
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<A HREF="http://www.mot.com/AECS/PNSB/products">Motorola Oncore GPS receivers</A>
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(Basic, PVT6, VP, UT, UT+, GT, GT+, SL, M12),
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as long as they support the <I>Motorola Binary Protocol</I>.
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<P>The three most interesting versions of the Oncore are the VP,
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the UT+, and the "Remote" which is a prepackaged UT+.
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The VP is no longer available.
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The Motorola evaluation kit
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can also be recommended, it interfaces to a PC straightaway, using the
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serial (DCD) or parallel port for PPS input and packs the
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receiver in a nice and sturdy box.
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Two less expensive interface kits are available from
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<A HREF="http://www.tapr.org">TAPR</A>.
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<BR>
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<CENTER><TABLE NOSAVE >
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<TR NOSAVE>
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<TD NOSAVE><IMG SRC="pic/oncore_utplusbig.gif" HEIGHT=124
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WIDTH=210></TD>
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<TD><IMG SRC="pic/oncore_evalbig.gif" HEIGHT=124 WIDTH=182></TD>
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<TD><IMG SRC="pic/oncore_remoteant.jpg" HEIGHT=188 WIDTH=178></TD>
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</TR>
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<TR>
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<TD>
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<CENTER>UT+ oncore</CENTER>
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</TD>
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<TD>
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<CENTER>Evaluation kit</CENTER>
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</TD>
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<TD>
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<CENTER>Oncore Remote</CENTER>
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</TD>
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</TR>
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</TABLE></CENTER>
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<P>The driver requires a standard <TT>PPS</TT> interface for the
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pulse-per-second output from the receiver. The serial data stream alone
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does not provide precision time stamps (0-50msec variance, according to
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the manual), whereas the PPS output is precise down to 50 nsec (1 sigma)
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for the VP/UT models.
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If you do not have the PPS signal available, then you should probably be using
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the NMEA driver rather than the Oncore driver.
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<P>The driver will use the "position hold" mode with
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user provided coordinates,
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the receivers built-in site-survey,
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or a similar algorithm implemented in this driver to determine the antenna position.
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<H4>
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Monitor Data</H4>
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The driver always puts a lot of useful information on the clockstats file,
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and when run with debugging can be quite chatty on stdout.
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When first starting to use the driver you should definitely review the information
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written to the clockstats file to verify that the driver is running correctly.
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<P>
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In addition, on platforms supporting Shared Memory, all of the messages
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received from the Oncore receiver are made available in shared memory for
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use by other programs.
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See the <A HREF=Oncore-SHMEM.htm> Oncore-SHMEM </A> manual page for
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information on how to use this option.
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For either debugging or using the SHMEM option, an Oncore Reference Manual
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for the specific receiver in use will be required.
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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
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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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Not used by this driver.</DD>
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</DL>
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<B>Additional Information</B>
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<P>The driver was initially developed on FreeBSD, and has since been tested
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on Linux, SunOS and Solaris.
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<P><B>Configuration</B>
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<P>There is a driver specific configuration file <TT>/etc/ntp.oncore</TT>
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that contains information on the startup mode, the location of the GPS
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receiver, an offset of the PPS signal from zero, and the cable delay.
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The offset shifts the PPS signal to avoid interrupt pileups `on' the second,
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and adjust the timestamp accordingly.
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See the driver source for information on this file.
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The default with no file is: no delay, no offset, and a site survey is done
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to get the location of the gps receiver.
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<P>The <TT>/etc/ntp.conf</TT> file will need a line of the form<BR>
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<TT> pps /dev/oncore.pps.0 [ assert/clear ] hardpps</TT><BR>
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if you want the oncore driver to control the kernel PLL.
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For more information, see the <A HREF=clockopt.htm>Reference Clock
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Options</A> page.
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<P><B>Performance</B>
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<P>Really good. With the VP/UT+, the generated PPS pulse is referenced
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to UTC(GPS) with better than 50 nsec (1 sigma) accuracy. The
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limiting factor will be the timebase of the computer and the precision
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with which you can timestamp the rising flank of the
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PPS signal.
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Using FreeBSD, a FPGA based Timecounter/PPS interface,
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and an ovenized quartz oscillator, that performance has been reproduced.
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For more details on this aspect: <A
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HREF="http://phk.freebsd.dk/rover.html">Sub-Microsecond
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timekeeping under FreeBSD</A>.
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<HR>
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<ADDRESS>
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Poul-Henning Kamp (phk@FreeBSD.org),
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Reg Clemens (reg@dwf.com)
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</ADDRESS>
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</BODY>
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</HTML>
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