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I agree - use the long form. I hate roll-overs. Even if the hardware is not being used, the data may live forever.<br>
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David N1HAC<br>
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<div class="moz-cite-prefix">On 10/21/19 3:56 PM, Engelke, Bill via TangerineSDR wrote:<br>
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<p class="MsoNormal">Tom – thanks for bringing this up, I definitely should have included it. Referring to
<a href="https://nam05.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftools.ietf.org%2Fhtml%2Frfc5905%23section-6&data=02%7C01%7CDavid.G.McGaw%40dartmouth.edu%7Cb3d75caa4d0d4ea87a7b08d75660ee74%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637072846649103511&sdata=5KP32zz8gGvM5QJd%2FXBgZC5Wl%2BohHcDyXxldWMo0u50%3D&reserved=0" originalsrc="https://tools.ietf.org/html/rfc5905#section-6" shash="EWy6fbwkgZYFji30YcVuc9jyXC7ujLNl0JBsFVF3jAEDdS9CZx4hjonBKbJ8UuOxYSQN00z8gBjnn24n11SarBWVOhjGrind6icpd7E9noYU73qwkZCviAr++MBqkGizoffKcq+fyGl2VgSl0WIMUnjavO0O2fxE3gcnvcxpMH0=" moz-do-not-send="true">
https://tools.ietf.org/html/rfc5905#section-6</a> .<o:p></o:p></p>
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<p class="MsoNormal">After thinking about this, I’m wondering: <b>should we consider using the full 128-bit NTP date format</b> (instead of the NTP Short format of 64 bits), with the idea that we then
<b>don’t have to cope with the year 2036 rollover</b>? The Era value will take care of it. Since our time stamps don’t occur all that often, it doesn’t seem to me like a big cost. Our experience has been that these software projects take on a life of their
own and last much longer than anyone ever expects; thinking of it in that way, 2037 is right around the corner.<o:p></o:p></p>
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<p class="MsoNormal">Would anyone else like to weigh in on this matter?<o:p></o:p></p>
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<p class="MsoNormal">73- Bill, AB4EJ<o:p></o:p></p>
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<p class="MsoNormal"><b>From:</b> TangerineSDR <a class="moz-txt-link-rfc2396E" href="mailto:tangerinesdr-bounces@lists.tapr.org">
<tangerinesdr-bounces@lists.tapr.org></a> <b>On Behalf Of </b>Tom McDermott via TangerineSDR<br>
<b>Sent:</b> Friday, October 18, 2019 4:29 PM<br>
<b>To:</b> TAPR TangerineSDR Modular Software Defined Radio <a class="moz-txt-link-rfc2396E" href="mailto:tangerinesdr@lists.tapr.org">
<tangerinesdr@lists.tapr.org></a><br>
<b>Cc:</b> Tom McDermott <a class="moz-txt-link-rfc2396E" href="mailto:tom.n5eg@gmail.com">
<tom.n5eg@gmail.com></a><br>
<b>Subject:</b> Re: [TangerineSDR] PSWS Time Stamping Concept<o:p></o:p></p>
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<p class="MsoNormal">HI Bill - thanks for documenting this. The format of the 64-bit time stamp <o:p></o:p></p>
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<p class="MsoNormal">should be referenced. My recommendation is NTP format. We cannot use all of<o:p></o:p></p>
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<p class="MsoNormal">the precision that affords, and thus may want to consider setting the LSBs to zero below<o:p></o:p></p>
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<p class="MsoNormal">some accuracy limit.<o:p></o:p></p>
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<p class="MsoNormal">The format is documented in: IETF RFC 5905 Section 6, "NTP Timestamp format", figure 3.<o:p></o:p></p>
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<p class="MsoNormal">page 13.<o:p></o:p></p>
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<p class="MsoNormal"> <a href="https://nam05.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftools.ietf.org%2Fhtml%2Frfc5905&data=02%7C01%7CDavid.G.McGaw%40dartmouth.edu%7Cb3d75caa4d0d4ea87a7b08d75660ee74%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637072846649113508&sdata=zvlyl8JGHwsOa0MuZwE4muXqne6TKMOf%2FE5GrIs3e%2FE%3D&reserved=0" originalsrc="https://tools.ietf.org/html/rfc5905" shash="wm4wRyzhQGC4nBo+F9K+PhSqR0wpvq+SAMNbPYUovv+FbBUarjdnZdaGlMhSGYq5oDys2+7oNGCrEVQ18O2ACOmaGav16BCLO5rUiULs7IJyuYsL1lPN0hCrodpFiQVEGb0PiDmH7epO1bH+qCffhibEcBsP77cNRLlePtOKtHs=" moz-do-not-send="true">
https://tools.ietf.org/html/rfc5905</a><o:p></o:p></p>
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<p class="MsoNormal">There are standard library tools to manipulate it. Whilst UNIX time will rollover in 2037,<o:p></o:p></p>
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<p class="MsoNormal">my view is that standard methods, procedures, and standard code will emerge to consistently handle it.<o:p></o:p></p>
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<p class="MsoNormal">If we adopt a proprietary format, then custom code would otherwise need to be crafted.<o:p></o:p></p>
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<p class="MsoNormal">The fractional portion of one second is encoded as a 32-bit integer. The LSB represents 0.233 nanoseconds.<o:p></o:p></p>
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<p class="MsoNormal">We could consider setting the 5 LSBs to zero for the 50 nanosecond-ish accuracy. Then use those LSBs<o:p></o:p></p>
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<p class="MsoNormal">later if some GPS receiver in the future had better accuracy.<o:p></o:p></p>
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<p class="MsoNormal">-- Tom, N5EG<o:p></o:p></p>
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<p class="MsoNormal">On Fri, Oct 18, 2019 at 1:09 PM Scotty Cowling via TangerineSDR <<a href="mailto:tangerinesdr@lists.tapr.org" moz-do-not-send="true">tangerinesdr@lists.tapr.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Hi Bill,<br>
<br>
Just to be clear, if the number of channels does not divide evenly into 1024, then a packet might not start with channel 0 I/Q samples.<br>
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Is there a requirement that the time stamp immediately precede channel 0 I/Q data? For example, a packet could look like this:<br>
<br>
CH0_I(0), CH0_Q(0), CH1_I(0), CH1_Q(0), CH2_I(0), CH2_Q(0), CH0_I(1), CH0_Q(1), CH1_1(1), CH1_Q(1), CH2_I(1), CH2_Q(1), CH0_I(2)...
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...CH2_I(339), CH2_Q(339), CH0_I(340), CH0_Q(340)<br>
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So you would start the next packet like this:<br>
CH1_I(340), CH1_Q(340), CH2_I(340), CH2_Q(340), CH0_I(341), CH0_Q(341)...<br>
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If I put the time stamp at the beginning:<br>
<sync><time stamp>CH1_I(340), CH1_Q(340), CH2_I(340), CH2_Q(340), CH0_I(341), CH0_Q(341)...<br>
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Then the time stamp would apply to the first and second I/Q pairs (CH1 and CH2) as well as to the last I/Q pair of the previous packet (CH0).<br>
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If I always put the time stamp before CH0, then the time stamp would apply to the last I/Q pair of one packet and also to the first two I/Q pairs of the next packet.<br>
<br>
So are the time stamps always before CH0, or can they be anywhere? I think for proper synchronization, they will have to be before CH0 only.<br>
<br>
Also, while it is clear that time stamps are sent periodically, that period is not specified anywhere. I think we need to specify that, don't we? Maximum count between timestamps? Maximum number of packets?<br>
<br>
Did you want to expand on the two commands (or methods) used by the SBC to set the two times (GPSDO and "best effort")? We talked about an "arm" command that causes the time to be set on the next 1 PPS transition and an "immediate" command that sets the time
immediately upon reception of the command.<br>
<br>
73,<br>
Scotty WA2DFI<o:p></o:p></p>
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<p class="MsoNormal">On 2019-10-17 17:37, Engelke, Bill via TangerineSDR wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">To all:
<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Attached is our proposed concept for Time Stamping for PSWS data – for your review and comment.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Note that this is primarily for the case where raw I/Q data is being stored in Digital RF format.
<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Data recording will be a bit different in the low-bandwidth case where the I/Q data is to be processed by GNURadio running on the SBC, and FFT (waterfall) results are uploaded to
the database.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Dave: please post to TangerineSDR.com<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">TNX ES 73 - W. D. Engelke (Bill), AB4EJ<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Center for Advanced Public Safety<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">The University of Alabama<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Tuscaloosa, AL 35487<o:p></o:p></p>
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<p class="MsoNormal">-- <br>
TangerineSDR mailing list<br>
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