[ntp:questions] NTP + PPS on Atom motherboards

Hahn, Ron ron.hahn at fmr.com
Wed Aug 1 17:10:52 UTC 2012


Thank you for these helpful advises. I am recalling many years ago there were such things as line transceivers that converted the signals from TTL-RS232 and backwards.  Do these still exist in the world and have you perhaps these part numbers?  I am thinking this is the only thing left to try. Except possibly changing the PPS pulse width.  Maybe with the Fat PPS board?  This is reminding me of the old days. Printers and Terminals! :)


From: Chris Albertson [mailto:albertson.chris at gmail.com]
Sent: 01 August 2012 16:40
To: Hahn, Ron
Cc: questions at lists.ntp.org
Subject: Re: [ntp:questions] NTP + PPS on Atom motherboards

All Serial ports are spec'd for RS232 voltage levels but many of then will still work on TTL levels.    My guess (I'm guessing because you don't say) is that you are feeding the serial port a TTL level signal.    The Core 2 Duo might be fine with this but perhaps the Atom board need "real rs232" and you will have the level convert the TTL.

I also had a problem like yours and it turned out to be the serial cable.  I was using about 100 feet of the wrong kind of wire because it was already pulled through the walls and down two floors.   I found I needed to use a balanced rs422 signal to go that far reliably.   But I ended up moving the computer and using a 3 foot cable.  BTW I was using an Atom as well and found that I had to give the serial ports on that board a very clean in-spec RS232 signal.

Guessing again, I doubt your ports are "bad" but they might be spec'd for rs232 while the core 2 boards are over-spec'd.

On Wed, Aug 1, 2012 at 1:46 AM, Hahn, Ron <ron.hahn at fmr.com<mailto:ron.hahn at fmr.com>> wrote:

I have been working for some time now trying to get four different Asus Atom motherboards to successfully work as a NTP stratum 1 server.  I am using the FreeBSD 8.3 OS with PPS compilation in the kernel, and the ntp-devel port (4.2.7p2?? version ntp).  Thanks to the David Taylor web site, I am using the Sure GPS boards to drive these motherboards and also his MRTG script to monitor these things too.

What I am seeing is that the time is off by almost 53,000uS on the MRTG graph and almost 500mS sometimes on the outputs of ntpq -c pe at times.  Other times it is a few uS from PPS.  I have been seeing this on three different boards (D525, D510, and 330 CPU) so this is repeating.  I was thinking this might be the tty port so I have tried both the tty ports and still the same.

I have used exactly the same recipe on a Core 2 Duo Tyan server and the times are maximally off by only +4uS/-2uS from PPS.  So I am thinking there is something fundamental wrong with the Atom boards.  I have repeated the experiments with a Pentium 4 server in another location and I am also seeing excellent timekeeping too.  I am thinking that maybe the Atom clock on the board is too consumer for these uses??

Has others experienced these difficulties with Atom motherboards as Stratum 1 servers?


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Chris Albertson
Redondo Beach, California

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