138 lines
4.0 KiB
HTML
138 lines
4.0 KiB
HTML
<HTML>
|
|
<HEAD>
|
|
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
|
|
<META NAME="GENERATOR" CONTENT="Mozilla/4.01 [en] (Win95; I) [Netscape]">
|
|
<TITLE>Trak 8820 GPS Receiver
|
|
</TITLE>
|
|
</HEAD>
|
|
<BODY>
|
|
|
|
<H3>
|
|
Trak 8820 GPS Receiver</H3>
|
|
|
|
<HR>
|
|
<H4>
|
|
Synopsis</H4>
|
|
Address: 127.127.2.<I>u</I>
|
|
<BR>Reference ID: <TT>GPS</TT>
|
|
<BR>Driver ID: <TT>GPS_TRAK</TT>
|
|
<BR>Serial Port: <TT>/dev/trak<I>u</I></TT>; 9600 baud, 8-bits, no parity
|
|
<BR>Features: <TT>tty_clk</TT>
|
|
<H4>
|
|
Description</H4>
|
|
This driver supports the Trak 8820 GPS Station Clock. The claimed accuracy
|
|
at the 1-PPS output is 200-300 ns relative to the broadcast signal; however,
|
|
in most cases the actual accuracy is limited by the precision of the timecode
|
|
and the latencies of the serial interface and operating system.
|
|
|
|
<P>For best accuracy, this radio requires the <TT>tty_clk</TT> line discipline,
|
|
which captures a timestamp at the <TT>*</TT> on-time character of the timecode.
|
|
Using this discipline the jitter is in the order of 1 ms and systematic
|
|
error about 0.5 ms. If unavailable, the buffer timestamp is used, which
|
|
is captured at the <TT>\r</TT> ending the timecode message. This introduces
|
|
a systematic error of 23 character times, or about 24 ms at 9600 bps, together
|
|
with a jitter well over 8 ms on Sun IPC-class machines.
|
|
|
|
<P>Using the menus, the radio should be set for 9600 bps, one stop bit
|
|
and no parity. It should be set to operate in computer (no echo) mode.
|
|
The timecode format includes neither the year nor leap-second warning.
|
|
|
|
<P>In operation, this driver sends a <TT>RQTS\r</TT> request to the radio
|
|
at initialization in order to put it in continuous time output mode. The
|
|
radio then sends the following message once each second:
|
|
<PRE>*RQTS U,ddd:hh:mm:ss.0,q<cr><lf>
|
|
|
|
on-time = '*'
|
|
ddd = day of year
|
|
hh:mm:ss = hours, minutes, seconds
|
|
q = quality indicator (phase error), 0-6:
|
|
0 > 20 us
|
|
6 > 10 us
|
|
5 > 1 us
|
|
4 > 100 ns
|
|
3 > 10 ns
|
|
2 < 10 ns</PRE>
|
|
The alarm condition is indicated by <TT>0</TT> at <TT>Q</TT>, which means
|
|
the radio has a phase error greater than 20 us relative to the broadcast
|
|
time. The absence of year, DST and leap-second warning in this format is
|
|
also alarmed.
|
|
|
|
<P>The continuous time mode is disabled using the <TT>RQTX\r</TT> request,
|
|
following which the radio sends a <TT>RQTX DONE<cr><lf></TT> response.
|
|
In the normal mode, other control and status requests are effective, including
|
|
the leap-second status request <TT>RQLS<cr></TT>. The radio responds
|
|
with <TT>RQLS yy,mm,dd<cr><lf></TT>, where <TT>yy,mm,dd</TT> are
|
|
the year, month and day. Presumably, this gives the epoch of the next leap
|
|
second, <TT>RQLS 00,00,00</TT> if none is specified in the GPS message.
|
|
Specified in this form, the information is generally useless and is ignored
|
|
by the driver.
|
|
<H4>
|
|
Monitor Data</H4>
|
|
When enabled by the <TT>flag4</TT> fudge flag, every received timecode
|
|
is written as-is to the <TT>clockstats</TT> file.
|
|
<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>
|
|
|
|
|
|
<P>Additional Information
|
|
|
|
<P><A HREF="refclock.htm">Reference Clock Drivers</A></DL>
|
|
|
|
<HR>
|
|
<ADDRESS>
|
|
David L. Mills (mills@udel.edu)</ADDRESS>
|
|
|
|
</BODY>
|
|
</HTML>
|