[time-nuts] NTP jitter with Linux

Azelio Boriani azelio.boriani at screen.it
Thu Apr 5 10:20:21 UTC 2012


>>On a side note, speaking of deterministic systems, why has no one built a
GPSDO with an FPGA yet? Or an NTP server? :)

Yes, I have: I have a GPSDO entirely on a 50Kgates FPGA (Spartan3 XC3S50)
without microprocessor. GPS is the iLotus M12M and OCXO is a Morion MV201,
the DAC is... well, not exactly the best choice but it is an AD5660 16bit
only, anyway it works.

On Thu, Apr 5, 2012 at 8:51 AM, David J Taylor <
david-taylor at blueyonder.co.uk> wrote:

> I asked this on an NTP list, got some guesses, but no knowledgeable
>> responses.
>>
> []
>
>  So, running a process(es) which keep the CPU completely busy reduces the
>> jitter. The busier, the better. Why? I'm guessing it has something to do
>> with interrupt latency, but why does a busy CPU make it more consistent -
>> I'd expect the opposite? The difference is very obvious.
>>
>> Is there something else I can do to keep the jitter low?
>>
>
> Mike, have you tried FreeBSD instead?  Does it show the same problems?
>
> Cheers,
> David
> --
> SatSignal software - quality software written to your requirements
> Web:  http://www.satsignal.eu
> Email:  david-taylor at blueyonder.co.uk
>
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