[ntp:questions] Fwd: Simulate PPS devices

Maximilian Brehm maximilian.brehm at tu-ilmenau.de
Thu Apr 10 14:24:07 UTC 2014

I wrote the message before I actually checked out shmpps. It seems 
that it does not use the Kernel-PPS interface but simply transmits a 
timestamp via the shared memory interface each second.

The reason I want to use the Kernel-PPS interface (RFC 2783 mentions 
that it supports asynchronous signals) and simulate devices is that it 
includes additional sanity checks. I guess I could alternatively 
implement the logic myself (could I?), that is, wait for a packet with 
an offset greater than one second compared to the last used package and 
pass it to my own PPS discipline.


-------- Original Message --------
Subject: [ntp:questions] Simulate PPS devices
Date: Thu, 10 Apr 2014 15:26:52 +0200
From: Maximilian Brehm <maximilian.brehm at tu-ilmenau.de>
To: <questions at lists.ntp.org>


so, I wrote a program to communicate with NTP via the shared
memory driver. It currently uses CLOCK_REALTIME and CLOCK_MONOTONIC to
simulate an offset and NTP wanders there correctly.

Now I would like
to include support for PPS. I found gpsd (http://gpsd.berlios.de/) and
shmpps (thanks to William Unruh,
http://pkgs.fedoraproject.org/cgit/shmpps.git/) for reference. As far 
I see they both rely on hardware devices and connections via serial or
parallel port or USB. I also found an interesting hack of shmpps using
/dev/rtc at http://www.wraith.sf.ca.us/ntp/#parallel-port. As 
in previous emails, I need the PPS signal to be simulated by analyzing
the timestamps of a packet stream from a reference system in a
destination system. The programs mentioned above use the Kernel-PPS
interface which relies on devices as far as I can see. So do you know 
proper way to approach this? Could I simulate a device similar to
/dev/rtc and make use of the hack?

Is this still the correct mailing
list for this purpose?



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