159 lines
4.7 KiB
HTML
159 lines
4.7 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
|
|
<HTML>
|
|
<HEAD>
|
|
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-
|
|
1">
|
|
<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/oncore.serial.0</TT>; 9600 baud, 8-bits,
|
|
no parity.<BR>
|
|
PPS Port: <TT>/dev/oncore.pps.0</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 three most interesting versions of the Oncore are the "VP",
|
|
the "UT+",
|
|
and the "Remote" which is a prepackaged "UT+".
|
|
The "VP" is no longer available.
|
|
The evaluation kit
|
|
can also be recommended, it interfaces to a PC straightaway, using the
|
|
serial (DCD) or parallel port for PPS input and packs the
|
|
receiver in a nice and sturdy box.
|
|
Two less expensive interface kits are available from
|
|
<A HREF="http://www.tapr.org">TAPR </A>.
|
|
|
|
<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 VP/UT models.
|
|
|
|
<P>The driver will use the "position hold" mode with
|
|
user provided coordinates,
|
|
the receivers built-in site-survey,
|
|
or a similar algorithm implemented in this driver to determine the antenna position.
|
|
<H4>
|
|
Monitor Data</H4>
|
|
The driver is quite chatty on stdout if ntpd is run with debugging.
|
|
<P>
|
|
In addition, on platforms supporting Shared Memory, all of the messages
|
|
received from the Oncore receiver are made available in shared memory for
|
|
use by other programs.
|
|
See the <A HREF=Oncore-SHMEM.htm> Oncore-SHMEM </A> manual page for
|
|
information on how to use this option.
|
|
For either debugging or using the SHMEM option, an Oncore Reference Manual
|
|
for the specific receiver in use will be required.
|
|
<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>
|
|
Not used by this driver.</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>
|
|
<P>The driver was initially developed on FreeBSD, and has since been tested
|
|
on Linux, SunOS and Solaris.
|
|
|
|
<P>There is a driver specific configuration file <TT>/etc/ntp.oncore</TT>
|
|
that contains information on the startup mode, the location of the GPS
|
|
receiver, an offset of the PPS signal from zero, and the cable delay.
|
|
The offset shifts the PPS signal to avoid interrupt pileups `on' the second,
|
|
and adjust the timestamp accordingly.
|
|
See the driver source for information on this file.
|
|
The default with no file is: no delay, no offset, and a site survey is done
|
|
to get the location of the gps receiver.
|
|
|
|
<P>The <TT>/etc/ntp.conf</TT> file will need a line of the form<BR>
|
|
|
|
<TT> pps /dev/oncore.pps.0 [ assert/clear ] hardpps</TT><BR>
|
|
if you want the oncore driver to control the kernel PLL.
|
|
For more information, see the <A HREF=clockopt.htm>Reference Clock
|
|
Options</A> page.
|
|
|
|
<P><B>Performance</B>
|
|
<P>Really good. With the VP/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),
|
|
Reg Clemens (reg@dwf.com)
|
|
</ADDRESS>
|
|
</BODY>
|
|
</HTML>
|