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<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal">I have a problem with linux pps on one of my system and I don’t know what might be happening.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ve setup the udev rules and ldattach service and I the 1PPS input on the DCD pin of the serial port is visible when I run ppstest:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">$ sudo ppstest /dev/pps0 <o:p></o:p></p>
<p class="MsoNormal">trying PPS source "/dev/pps0"<o:p></o:p></p>
<p class="MsoNormal">found PPS source "/dev/pps0"<o:p></o:p></p>
<p class="MsoNormal">ok, found 1 source(s), now start fetching data...<o:p></o:p></p>
<p class="MsoNormal">source 0 - assert 0.000000000, sequence: 0 - clear 1679941271.001319474, sequence: 97<o:p></o:p></p>
<p class="MsoNormal">source 0 - assert 0.000000000, sequence: 0 - clear 1679941272.001326292, sequence: 98<o:p></o:p></p>
<p class="MsoNormal">source 0 - assert 0.000000000, sequence: 0 - clear 1679941273.001330757, sequence: 99<o:p></o:p></p>
<p class="MsoNormal">source 0 - assert 0.000000000, sequence: 0 - clear 1679941274.001335713, sequence: 100<o:p></o:p></p>
<p class="MsoNormal">source 0 - assert 0.000000000, sequence: 0 - clear 1679941275.001341371, sequence: 101<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">But as you can see from the output above, *<b>only the clear edge is captured</b>*, not the assert edge. I looked at the pulse with a scope and the pulse is a positive pulse (leading edge is rising edge), 5.55Vpp. I don’t understand why
it would detect the clear edge, but not the assert edge.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ve searched online for a possible explanation of these symptoms but with no success.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Does anyone know what might be the root cause of this or where I should look to troubleshoot this?<o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">Any information on this would be much appreciated.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">Setup details:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">System: CentOS Linux release 7.9.2009 (Core), kernel 3.10.0-1160.83.1.el7.x86_64<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">ldattach script and udev rules shown below:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">$ cat /usr/lib/systemd/system/ldattach@.service<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">[Unit]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">Description=1PPS input on /dev/%i<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">Before=ntpd.service<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">[Service]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">ExecStart=/sbin/ldattach 18 /dev/%i<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">Type=forking<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">[Install]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">WantedBy=multi-user.target<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="FR-CA" style="color:#1F497D;mso-fareast-language:EN-CA">$ cat /etc/udev/rules.d/09-pps.rules<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">KERNEL=="pps0", OWNER="root", GROUP="root", MODE="0644"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">KERNEL=="ttyS0", RUN+="/bin/setserial -v /dev/%k low_latency irq 4"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA"> Andre<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">--</span><span style="color:#1F497D;mso-fareast-language:EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">Andre Charbonneau<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">Frequency & Time<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">Metrology Research Centre<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA">National Research Council Canada / Government of Canada<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA"><a href="mailto:andre.charbonneau@nrc-cnrc.gc.ca"><span style="color:blue">andre.charbonneau@nrc-cnrc.gc.ca</span></a> / 613-993-3129<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="FR-CA" style="color:#1F497D;mso-fareast-language:EN-CA">Fréquence et temps<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="FR-CA" style="color:#1F497D;mso-fareast-language:EN-CA">Centre de recherche en métrologie<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="FR-CA" style="color:#1F497D;mso-fareast-language:EN-CA">Conseil national de recherches Canada / Gouvernement du Canada<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-CA"><a href="mailto:andre.charbonneau@nrc-cnrc.gc.ca"><span lang="FR-CA" style="color:blue">andre.charbonneau@nrc-cnrc.gc.ca</span></a></span><span lang="FR-CA" style="color:#1F497D;mso-fareast-language:EN-CA">
/ 613-993-3129<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="FR-CA"><o:p> </o:p></span></p>
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