[ntp:questions] Assistance with PPS on Windows

Ken Link klink at numberzero.org
Wed May 4 22:20:33 UTC 2011

It appears all I needed to do was swap the TX and CD pins to get it to
start polling and synced to PPS. Thanks!

Now, a behavioral question. Will PPS be selected as the peer if and
only if the peer marked "preferred" is also synced? What if I want PPS
to act as a supplement to whichever of the stratum 1+ peers NTP sees
available and decides to sync to? PPS will be the only stratum 0
reference source available to this system, but if the preferred peer
goes down I would expect PPS to continue to correct the jitter of
whichever other peer NTP decides to sync to (that doesn't seem to be
the case).

Also, it appears that while the preferred peer continues to be synced
and polled every 64 seconds, the PPS peer seems to "toggle" from being
a PPS peer to being rejected nearly every poll (of 16 seconds). Is
this because the polling rate is different between the PPS source and
the other sources, or is my serial cable too jittery? The PPS source
claims to have an offset of +/- 10 ms and a jitter of between 2-3 ms
depending on the poll.


On Wed, May 4, 2011 at 2:11 PM, Ken Link <klink at numberzero.org> wrote:
> Cool program. We've got a physical adapter that does the same thing.
> We're using DB9-to-RJ45 adapters throughout our serial network and it
> appears I'm not using the correct RJ45-to-DB9 adapter to move the PPS
> signal to the DCD pin. I'll post back when I make the right adapter
> and get a chance to test again.
> That would probably explain why ntpd is seeing a 413279.091756s offset, huh.
> Ken
> On Wed, May 4, 2011 at 9:56 AM, David J Taylor
> <david-taylor at blueyonder.co.uk.invalid> wrote:
>> []
>>> The problem is we cannot get NTP to sync to the PPS output. The PPS
>>> source shows up in “ntpq –p” however it has 0 reach. System B is
>>> synced to System A and is a stable Stratum 2 server at the moment.
>>> MbgMon on System B shows the PPS output on the card is active. The
>>> IRIG signal is 100% and shows it is synced. I’ve installed the
>>> serialpps driver, rebooted and verified it was loaded in the Device
>>> Manager, set the PPSAPI_DLLS global environment variable
>>> appropriately, etc.
>>> Any suggestions on how to troubleshoot this?
>>> Thanks,
>>> Ken
>> Ken, Dave Hart is the expert in the PPS on Windows.  Could I suggest that
>> you at least check that the pulses are being seen by checking with my Serial
>> Port LEDs program?
>>  http://www.satsignal.eu/software/net.htm#SerialPortLEDs
>> With NTP not running (as only one device can access the COM port), see
>> whether there are brief white flashes on the DCD line.
>> Cheers,
>> David
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