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<div><span style="font-size: 13.3333px;">Kip,</span></div>
<div><span style="font-size: 13.3333px;"><br>
</span></div>
<div><span style="font-size: 13.3333px;">Thanks for writing.</span></div>
<div><span style="font-size: 13.3333px;"><br>
</span></div>
<div><span style="font-size: 13.3333px;">As you probably read, Murray and Dave also recommended GPSDO, which I had rejected for size, weight, and cost, but Murray pointed me to a tiny, light, affordable GPS receiver with PPS. And then I realized I could characterize the CPU's TSC and use TSC without an external reference.</span></div>
<div><span style="font-size: 13.3333px;"><br>
</span></div>
<div><span style="font-size: 13.3333px;">Then I realized I was calibrating the wrong reference: TSC tells me when the data are processed, not when they are sampled. TSC can tell me precisely when the processing takes place, but that is irrelevant. TSC is great for benchmarking, but I need a timestamp. That timestamp already exists:</span></div>
<div><span style="font-size: 13.3333px;"><br>
</span></div>
<div><span style="font-size: 13.3333px;">Playrec, which uses portaudio, counts every sample coming from the audio adapter, regardless of whether the sample is processed. That means that "lost" samples are also counted, so the sample count is correct. The sample count is my timestamp. (Playrec also has an extremely coarse getStreamStartTime command, but its resolution is whole integer seconds.)</span></div>
<div><span style="font-size: 13.3333px;"><br>
</span></div>
<div><span style="font-size: 13.3333px;">I am not sure whether playrec/portaudio uses the audio adapter's clock or whether it resamples using the CPU's clock. In my application, that's irrelevant because each audio adapter is on a separate CPU, so whichever clock is being used is the clock that I need to characterize. So now I will characterize the sample rates of the three audio adapters in the localizer and I think I'll have what I need.</span></div>
<div><span style="font-size: 13.3333px;"><br>
</span></div>
<div><span style="font-size: 13.3333px;">Thank you all for getting me to think about what's really needed. I was about to add unnecessary hardware and collect unnecessary timing information. The existing parts of the localizer already have what I need. I just didn't see it before.</span></div>
<div><span style="font-size: 13.3333px;"><br>
</span></div>
<div><span style="font-size: 13.3333px;">In the future, if I need an accurate, cheap, small, lightweight timing reference, I will look at GPS PPS again.</span></div>
<div><span style="font-size: 13.3333px;"><br>
</span></div>
<div><span style="font-size: 13.3333px;">Later,</span></div>
<div><span style="font-size: 13.3333px;">John Swindle</span></div>
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<div style="font-family:arial,helvetica;font-size:10pt;color:black">-----Original Message-----<br>
From: Kipton Moravec via DPRGlist <dprglist@lists.dprg.org><br>
To: dprglist@lists.dprg.org<br>
Sent: Mon, Jun 8, 2020 3:39 pm<br>
Subject: Re: [Dprglist] Stability of CPU oscillator<br>
<br>
<div id="yiv5290810830">
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<div>Look at a GPSDO GPS Disclipined Oscillator if you need more
accuracy (and more cost) <br clear="none">
<br clear="none">
<a rel="nofollow" shape="rect" class="yiv5290810830moz-txt-link-freetext" target="_blank" href="https://en.wikipedia.org/wiki/GPS_disciplined_oscillator">https://en.wikipedia.org/wiki/GPS_disciplined_oscillator</a><br clear="none">
<br clear="none">
Some quick examples in the $50 to $80 range. 10 MHz<br clear="none">
<br clear="none">
<a rel="nofollow" shape="rect" class="yiv5290810830moz-txt-link-freetext" target="_blank" href="https://www.digikey.com/product-detail/en/mikroelektronika/MIKROE-1032/1471-1009-ND/4495374?utm_adgroup=Evaluation%20Boards%20-%20Expansion%20Boards%2C%20Daughter%20Cards&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_Product_Development%20Boards%2C%20Kits%2C%20Programmers_NEW&utm_term=&utm_content=Evaluation%20Boards%20-%20Expansion%20Boards%2C%20Daughter%20Cards&gclid=Cj0KCQjww_f2BRC-ARIsAP3zarGwf8Rd71SgPkxbg_0s2pf5COe-2X_HmcmN8cce9yr8Wgjz1RYF7v0aAn3cEALw_wcB">https://www.digikey.com/product-detail/en/mikroelektronika/MIKROE-1032/1471-1009-ND/4495374?utm_adgroup=Evaluation%20Boards%20-%20Expansion%20Boards%2C%20Daughter%20Cards&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_Product_Development%20Boards%2C%20Kits%2C%20Programmers_NEW&utm_term=&utm_content=Evaluation%20Boards%20-%20Expansion%20Boards%2C%20Daughter%20Cards&gclid=Cj0KCQjww_f2BRC-ARIsAP3zarGwf8Rd71SgPkxbg_0s2pf5COe-2X_HmcmN8cce9yr8Wgjz1RYF7v0aAn3cEALw_wcB</a><br clear="none">
<br clear="none">
<a rel="nofollow" shape="rect" class="yiv5290810830moz-txt-link-freetext" target="_blank" href="https://www.digikey.com/product-detail/en/sparkfun-electronics/GPS-11858/1568-1151-ND/5673737?utm_adgroup=RF%20Evaluation%20and%20Development%20Kits%2C%20Boards&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_Product_RF%2FIF%20and%20RFID_NEW&utm_term=&utm_content=RF%20Evaluation%20and%20Development%20Kits%2C%20Boards&gclid=Cj0KCQjww_f2BRC-ARIsAP3zarGq8wQ9V83W1qbV6_vM8a6ndNj-zvWG1dwi5Rn1boW5lpTu2B_BTpkaAohUEALw_wcB">https://www.digikey.com/product-detail/en/sparkfun-electronics/GPS-11858/1568-1151-ND/5673737?utm_adgroup=RF%20Evaluation%20and%20Development%20Kits%2C%20Boards&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_Product_RF%2FIF%20and%20RFID_NEW&utm_term=&utm_content=RF%20Evaluation%20and%20Development%20Kits%2C%20Boards&gclid=Cj0KCQjww_f2BRC-ARIsAP3zarGq8wQ9V83W1qbV6_vM8a6ndNj-zvWG1dwi5Rn1boW5lpTu2B_BTpkaAohUEALw_wcB</a><br clear="none">
<br clear="none">
No prices but you can find them probably on Mouser or Digikey. <br clear="none">
<a rel="nofollow" shape="rect" class="yiv5290810830moz-txt-link-freetext" target="_blank" href="https://www.microsemi.com/product-directory/clocks-frequency-references/3826-gps-disciplined-oscillators-gpsdo">https://www.microsemi.com/product-directory/clocks-frequency-references/3826-gps-disciplined-oscillators-gpsdo</a><br clear="none">
<br clear="none">
Finally you can see what is at EBAY when looking for a 10 MHz
reference.<br clear="none">
<br clear="none">
<a rel="nofollow" shape="rect" class="yiv5290810830moz-txt-link-freetext" target="_blank" href="https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313.TR3.TRC2.A0.H0.X10+MHz+reference.TRS0&_nkw=10+MHz+reference&_sacat=0">https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313.TR3.TRC2.A0.H0.X10+MHz+reference.TRS0&_nkw=10+MHz+reference&_sacat=0</a><br clear="none">
<br clear="none">
Kip<br clear="none">
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<div class="yiv5290810830yqt4212743768" id="yiv5290810830yqt41803">
<div class="yiv5290810830moz-cite-prefix">On 6/4/20 9:55 PM, John Swindle via
DPRGlist wrote:<br clear="none">
</div>
<blockquote type="cite">
</blockquote></div>
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<div class="yiv5290810830yqt4212743768" id="yiv5290810830yqt62265">
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<div style="color:black;font:10pt Arial, Helvetica, sans-serif;">Folks:
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</div>
<div>What is the typical stability of the oscillator in a
consumer x86 platform?</div>
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</div>
<div>I don't find that specified for systems, or I don't know
where to look for the spec. The part numbers on the crystal
often don't seem to be sufficient to find the stability in the
XTAL datasheet.</div>
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</div>
<div>I don't have access to test equipment to measure it.</div>
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</div>
<div>I appreciate any help, but just to be clear: I'm asking
about the stability, not the accuracy, so it would be ppm of
drift and/or jitter over time, not ppm of accuracy.</div>
<div><br clear="none">
</div>
<div>I intend to use the invariant TSC in x86 processors, but if
the oscillator is not stable, then the invariant TSC numbers
will not be as useful to me.</div>
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<div>Thanks.</div>
<div><br clear="none">
</div>
<div>John Swindle</div>
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</div>
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