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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<META NAME="GENERATOR" CONTENT="Mozilla/4.06 [en] (X11; I; FreeBSD
3.0-CURRENT i386) [Netscape]">
<TITLE>Motorola Oncore GPS Receiver
</TITLE>
</HEAD>
<BODY>
<H3>
Motorola Oncore GPS receiver</H3>
<HR>
<H4>
Synopsis</H4>
Address: 127.127.30.0
<BR>Reference ID: <TT>GPS</TT>
<BR>Driver ID: ONCORE
<BR>Serial Port: <TT>/dev/cuaa0</TT>; 9600 baud, 8-bits, no parity
<BR>PPS Port: <TT>/dev/xpps0</TT>; <TT>PPS_CAPTUREASSERT</TT>
required, <TT>PPS_OFFSETASSERT</TT> supported.
<H4>
Description</H4>
This driver supports various models of the <A
HREF="http://www.mot.com/AECS/PNSB/products">Motorola Oncore GPS
receivers</A>. as long as they support the <I>Motorola Binary
Protocol</I>.
<P>The two most interesting version of the Oncore are the "UT+"
and the "Remote" which is a prepackaged "UT+". The evaluation kit
can also be recommended, it interfaces to a PC straightaway, using the
parallel port for PPS input (supported under FreeBSD), and packs the
receiver in a nice and sturdy box.
<BR>
<CENTER><TABLE NOSAVE >
<TR NOSAVE>
<TD NOSAVE><IMG SRC="pic/oncore_utplusbig.gif" HEIGHT=124
WIDTH=210></TD>
<TD><IMG SRC="pic/oncore_evalbig.gif" HEIGHT=124 WIDTH=182></TD>
<TD><IMG SRC="pic/oncore_remoteant.jpg" HEIGHT=188 WIDTH=178></TD>
</TR>
<TR>
<TD>
<CENTER>UT+ oncore</CENTER>
</TD>
<TD>
<CENTER>Evaluation kit</CENTER>
</TD>
<TD>
<CENTER>Oncore Remote</CENTER>
</TD>
</TR>
</TABLE></CENTER>
<P>The driver requires a standard <TT>PPS</TT> interface for the pulse-
per-second output from the receiver. The serial data stream alone
does not provide precision time stamps (0-50msec variance, according to
the manual), whereas the PPS output is precise down to 50 nsec (1 sigma)
for the UT models. <P>The driver will use the "position hold" mode if
available, with either the receivers built-in site-survey or a similar
algorithm implemented in this driver.
<H4>
Monitor Data</H4>
The driver is quite chatty on stdout if ntpd is run with
debugging.
A manual will be required though.
<H4>
Fudge Factors</H4>
<DL>
<DT>
<TT>time1 <I>time</I></TT></DT>
<DD>
Specifies the time offset calibration factor, in seconds and fraction,
with default 0.0.</DD>
<DT>
<TT>time2 <I>time</I></TT></DT>
<DD>
Not used by this driver.</DD>
<DT>
<TT>stratum <I>number</I></TT></DT>
<DD>
Specifies the driver stratum, in decimal from 0 to 15, with default
0.</DD>
<DT>
<TT>refid <I>string</I></TT></DT>
<DD>
Specifies the driver reference identifier, an ASCII string from one to
four characters, with default <TT>GPS</TT>.</DD>
<DT>
<TT>flag1 0 | 1</TT></DT>
<DD>
Not used by this driver.</DD>
<DT>
<TT>flag2 0 | 1</TT></DT>
<DD>
Assume GPS receiver is on a mobile platform if set.</DD>
<DT>
<TT>flag3 0 | 1</TT></DT>
<DD>
Not used by this driver.</DD>
<DT>
<TT>flag4 0 | 1</TT></DT>
<DD>
Not used by this driver.</DD>
</DL>
<B>Additional Information</B><B></B>
<P>The driver has been developed under FreeBSD, and may still be pretty
FreeBSD centric. Patches are most welcome.
<P><B>Performance</B><B></B>
<P>Really good. With the UT+, the generated PPS pulse is
referenced
to UTC(GPS) with better than 50 nsec (1 sigma) accuracy. The
limiting factor will be the timebase of the computer and the precision
with which you can timestamp the rising flank of the
PPS signal.
Using FreeBSD, a FPGA based Timecounter/PPS interface
and
an ovenized quartz oscillator, that performance has been reproduced.
For
more details on this aspect: <A
HREF="http://phk.freebsd.dk/rover.html">Sub-Microsecond
timekeeping under FreeBSD</A>
<HR>
<ADDRESS>
Poul-Henning Kamp (phk@FreeBSD.org)</ADDRESS>
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