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Hi Hal,<br>
<br>
<div class="moz-cite-prefix">On 6/30/2018 0:26 AM, Hal Murray wrote:<br>
</div>
<blockquote type="cite"
cite="mid:20180630072636.D1AA340605C@ip-64-139-1-69.sjc.megapath.net">
<pre class="moz-quote-pre" wrap="">What's in your ntp.conf?</pre>
</blockquote>
<tt>refclock shm unit 1 refid PPS minpoll 0 maxpoll 0 prefer</tt><tt><br>
</tt><tt>refclock shm unit 0 refid GPS time1 .40 noselect</tt><tt><br>
</tt><tt><br>
</tt><tt>server clock.fmt.he.net minpoll 5 maxpoll 10
iburst # Fremont</tt><tt><br>
</tt><tt>server clock.sjc.he.net minpoll 5 maxpoll 10
iburst # San Jose</tt><tt><br>
</tt><tt>server clepsydra.dec.com minpoll 5 maxpoll 10
iburst # Palo Alto</tt><tt><br>
</tt><tt>server stratum-1.sjc02.svwh.net minpoll 5 maxpoll 10
iburst # San Jose</tt><tt><br>
</tt><tt>server gpstime.la-archdiocese.net minpoll 5 maxpoll 10
iburst # Los Angeles</tt><tt><br>
</tt><tt><br>
</tt><tt>restrict 0.0.0.0/0 limited nomodify nopeer noquery</tt><tt><br>
</tt><tt>restrict 127.0.0.1</tt><tt><br>
</tt><tt>restrict 192.168.1.222</tt><tt><br>
</tt><tt><br>
</tt><tt>leapfile /var/lib/ntp/leap-seconds.list</tt><tt><br>
</tt><tt>logfile /var/log/ntp.log</tt><tt><br>
</tt><tt>driftfile /var/lib/ntp/ntp.drift</tt><tt><br>
</tt><tt>statsdir /var/log/ntpstats/</tt><tt><br>
</tt><tt>statistics loopstats peerstats clockstats</tt><tt><br>
</tt><tt>filegen loopstats file loopstats type day enable</tt><tt><br>
</tt><tt>filegen peerstats file peerstats type day enable</tt><tt><br>
</tt><tt>filegen clockstats file clockstats type day enable</tt><br>
<br>
<blockquote type="cite"
cite="mid:20180630072636.D1AA340605C@ip-64-139-1-69.sjc.megapath.net">
<pre class="moz-quote-pre" wrap="">You might try increasing any maxpolls if they are less than 6. It's likely to
make the normal case worse, but if the spikes get better that might tell
you/us something.</pre>
</blockquote>
I think I'm good above in the ntp.conf, right?<br>
<br>
<blockquote type="cite"
cite="mid:20180630072636.D1AA340605C@ip-64-139-1-69.sjc.megapath.net">
<pre class="moz-quote-pre" wrap="">Do you have full logging?
logfile /var/log/xxx
logconfig =syncall +clockall +peerall +sysall</pre>
</blockquote>
Hmm - wasn't even familiar with logconfig until I looked it up just
now. I think I'm okay, the manpage says that everything is on by
default.<br>
<blockquote type="cite"
cite="mid:20180630072636.D1AA340605C@ip-64-139-1-69.sjc.megapath.net">
<pre class="moz-quote-pre" wrap="">There might be something interesting in there.
You might try putting all the log files into a memory file system. Maybe the
disk writes are disabling interrupts long enough to cause troubles. Or try a
USB hard drive.</pre>
</blockquote>
Yeah, I definitely need to try this. I know that any significant fs
activity will cause spikes. And there's a nice setup out there that
will write to memory fs, and flush back to disk when rebooting. I've
tried adjusting the 'commit' interval both longer (60s) and shorter
(5s) but no apparent difference.<br>
<blockquote type="cite"
cite="mid:20180630072636.D1AA340605C@ip-64-139-1-69.sjc.megapath.net">
<pre class="moz-quote-pre" wrap="">If you run out of other ideas, try without gpsd. Use the NMEA and PPS drivers.</pre>
</blockquote>
This is new to me too. I thought you had to run gpsd to send the
data from the GPS to ntpd. I'll look into this.<br>
<blockquote type="cite"
cite="mid:20180630072636.D1AA340605C@ip-64-139-1-69.sjc.megapath.net">
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">I have a thin, closed-cell insulation sheet affixed to the back of the GPS
hat to slow temp variations coming from the Raspi itself
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">
The temperature of the GPS isn't important. Time comes from the crystal that
drives the CPU. I think it's on the bottom of the board.
</pre>
</blockquote>
<br>
Another area of confusion for me here. The datasheet for the MT3339
specifically mentions 'reference oscillator' - <br>
<h3 class="platform__h3--margin" style="box-sizing: border-box;
font-family: RionaSans, Helvetica, 微軟正黑體, "Microsoft
JhengHei", 黑體-繁, "Heiti TC", 新細明體, PMingLiU,
sans-serif; font-weight: 700; line-height: 1.1; color: rgb(53, 54,
48); margin-top: 0px; margin-bottom: 0px; font-size: 20px;
font-style: normal; font-variant-ligatures: normal;
font-variant-caps: normal; letter-spacing: normal; orphans: 2;
text-align: start; text-indent: 0px; text-transform: none;
white-space: normal; widows: 2; word-spacing: 0px;
-webkit-text-stroke-width: 0px; background-color: rgb(245, 245,
245); text-decoration-style: initial; text-decoration-color:
initial;">Reference oscillator</h3>
<ul class="listContainer" style="box-sizing: border-box; margin-top:
0px; margin-bottom: 0px; padding-left: 1.5em; color: rgb(53, 54,
48); font-family: RionaSans, Helvetica, 微軟正黑體, "Microsoft
JhengHei", 黑體-繁, "Heiti TC", 新細明體, PMingLiU,
sans-serif; font-size: 14px; font-style: normal;
font-variant-ligatures: normal; font-variant-caps: normal;
font-weight: 400; letter-spacing: normal; orphans: 2; text-align:
start; text-indent: 0px; text-transform: none; white-space:
normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width:
0px; background-color: rgb(245, 245, 245); text-decoration-style:
initial; text-decoration-color: initial;">
<li style="box-sizing: border-box; margin-top: 5px;">
<p style="box-sizing: border-box; margin: initial; font-size:
14px; font-family: Roboto, Helvetica, 微軟正黑體, "Microsoft
JhengHei", 黑體-繁, "Heiti TC", 新細明體, PMingLiU,
sans-serif; line-height: 1.5em;">TCXO Frequency 16.368 MHz,
12.6 ~ 40 MHz</p>
</li>
<li style="box-sizing: border-box; margin-top: 5px;">
<p style="box-sizing: border-box; margin: initial; font-size:
14px; font-family: Roboto, Helvetica, 微軟正黑體, "Microsoft
JhengHei", 黑體-繁, "Heiti TC", 新細明體, PMingLiU,
sans-serif; line-height: 1.5em;">TCXO Frequency variation:
±2.0 ppm</p>
</li>
<li style="box-sizing: border-box; margin-top: 5px;">
<p style="box-sizing: border-box; margin: initial; font-size:
14px; font-family: Roboto, Helvetica, 微軟正黑體, "Microsoft
JhengHei", 黑體-繁, "Heiti TC", 新細明體, PMingLiU,
sans-serif; line-height: 1.5em;">Crystal Frequency: 26 MHz,
12.6 ~ 40.0 MHz</p>
</li>
<li style="box-sizing: border-box; margin-top: 5px;">
<p style="box-sizing: border-box; margin: initial; font-size:
14px; font-family: Roboto, Helvetica, 微軟正黑體, "Microsoft
JhengHei", 黑體-繁, "Heiti TC", 新細明體, PMingLiU,
sans-serif; line-height: 1.5em;">Crystal Frequency accuracy:
±10 ppm</p>
</li>
</ul>
<br class="Apple-interchange-newline">
So based on that, I assumed that controlling the temp of that
crystal would be a good thing too. But then, looking at those specs,
+/- 2ppm is horrendous, compared to the PPS's +/- 10ns. So it would
seem the gps crystal is quite irrelevant...<br>
<br>
Perhaps a thermal (conductive) pad on the bottom of the board to
draw heat away from the crystal might be good...<br>
<br>
Thanks for the suggestions/insights, Hal. I'll be poking around all
day it looks like!<br>
<br>
<br>
<pre class="moz-signature" cols="72">--
Paul Theodoropoulos
<a class="moz-txt-link-abbreviated" href="http://www.anastrophe.com">www.anastrophe.com</a>
</pre>
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