[ntp:questions] NTP + PPS on Atom motherboards

Chris Albertson albertson.chris at gmail.com
Wed Aug 1 15:40:15 UTC 2012

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> wrote:

> Colleagues,
> 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?
> Thanks,
> Ron
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Chris Albertson
Redondo Beach, California

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