117 lines
3.9 KiB
HTML
117 lines
3.9 KiB
HTML
<!-- $NetBSD: driver2.html,v 1.1 1998/12/30 20:20:34 mcr Exp $ -->
|
|
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML Strict//EN">
|
|
<html><head><title>
|
|
Trak 8820 GPS Receiver
|
|
</title></head><body><h3>
|
|
Trak 8820 GPS Receiver
|
|
</h3><hr>
|
|
|
|
<p><h4>Synopsis</h4>
|
|
|
|
<p>Address: 127.127.2.<var>u</var>
|
|
<br>Reference ID: GPS
|
|
<br>Driver ID: GPS-TRAK
|
|
<br>Serial Port: <code>/dev/trak<var>u</var></code>; 9600 baud, 8-bits,
|
|
no parity
|
|
<br>Features: <code>tty_clk, ppsclock</code>
|
|
|
|
<p><h4>Description</h4>
|
|
|
|
<p>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 <code>tty_clk</code> line
|
|
discipline, which captures a timestamp at the <code>*</code> 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 <code>\r</code>
|
|
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 <code>RQTS\r</code> 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>
|
|
|
|
<p>The alarm condition is indicated by <code>0</code> at <code>Q</code>,
|
|
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 <code>RQTX\r</code>
|
|
request, following which the radio sends a <code>RQTX
|
|
DONE<cr><lf></code> response. In the normal mode, other
|
|
control and status requests are effective, including the leap-second
|
|
status request <code>RQLS<cr></code>. The radio responds with
|
|
<code>RQLS yy,mm,dd<cr><lf></code>, where
|
|
<code>yy,mm,dd</code> are the year, month and day. Presumably, this
|
|
gives the epoch of the next leap second, <code>RQLS 00,00,00</code> if
|
|
none is specified in the GPS message. Specified in this form, the
|
|
information is generally useless and is ignored by the driver.
|
|
|
|
<p><h4>Monitor Data</h4>
|
|
|
|
<p>When enabled by the <code>flag4</code> fudge flag, every received
|
|
timecode is written as-is to the <code>clockstats</code> file.
|
|
|
|
<p><h4>Fudge Factors</h4>
|
|
|
|
<dl>
|
|
|
|
<dt><code>time1 <var>time</var></code>
|
|
<dd>Specifies the time offset calibration factor, in seconds and
|
|
fraction, with default 0.0.
|
|
|
|
<p><dt><code>time2 <var>time</var></code>
|
|
<dd>Not used by this driver.
|
|
|
|
<p><dt><code>stratum <var>number</var></code>
|
|
<dd>Specifies the driver stratum, in decimal from 0 to 15, with default
|
|
0.
|
|
|
|
<p><dt><code>refid <var>string</var></code>
|
|
<dd>Specifies the driver reference identifier, an ASCII string from one
|
|
to four characters, with default <code>TRAK</code>.
|
|
|
|
<p><dt><code>flag1 0 | 1</code>
|
|
<dd>Not used by this driver.
|
|
|
|
<p><dt><code>flag2 0 | 1</code>
|
|
<dd>Not used by this driver.
|
|
|
|
<p><dt><code>flag3 0 | 1</code>
|
|
<dd>Not used by this driver.
|
|
|
|
<p><dt><code>flag4 0 | 1</code>
|
|
<dd>Enable <code>clockstats</code> recording if set.
|
|
|
|
<p>Additional Information
|
|
|
|
<p><a href="refclock.html"> Reference Clock Drivers</a>
|
|
|
|
</dl>
|
|
|
|
<hr><address>David L. Mills (mills@udel.edu)</address></body></html>
|