[ntp:questions] Red Hat vote for chrony

David Lord snews at lordynet.org
Sat Dec 6 15:53:34 UTC 2014


Charles Swiger wrote:
> On Dec 5, 2014, at 5:55 PM, Paul <tik-tok at bodosom.net> wrote:
> [ ... ]
>>> Even back in 2002 with very inexpensive commodity hardware, FreeBSD was
>>> able to achieve accuracy measured to ~260 nanoseconds:
>> Hmmmm.  So phk uses a $1,500 rubidium standard as a system oscillator and
>> you call it inexpensive and commodity.
> 
> No, he used a $1500 rubidium clock to accurately measure the timekeeping
> quality of a $220 Soekris computer, and concluded:
> 
> "I have earlier complained that no good and cheap hardware were available which could timestamp a PPS signal reliably and precisely but now the Soekris computer has proven that it does indeed deliver just that: With a pricetag of approx USD220 (single unit including enclosure) this is the best hardware you can find for a stratum 1 NTP server."
> 
> If you wanted to drive such hardware via a ~$40 GPS puck, you'd probably
> see an accuracy of around a microsecond, perhaps a bit worse depending
> on the timekeeping accuracy which the GPS puck provides.  That was also
> the level of accuracy I was seeing from generic Intel hardware running
> FreeBSD as a stratum 1 with a GPS source.
> 
> I've used a digital frequency counter which had an onboard TCXO (or possibly
> a DTCXO) for measuring.  Although the frequency counter supported receiving
> higher-quality PPS timing from an external atomic clock, I've never had a
> Cs or Rb source, so I won't claim to have measured sub-microsecond accuracy with it.
> 
>> He also ran a particular install of BSD and a non-standard NTP.
> 
> I believe he ran FreeBSD 4.x and likely the ntpd from ports.
> 
> Regards,

Not quite

I believe this clock project needed a little work with soldering
iron and also ntpd/freebsd had to be modified to support the
sc520 gpio.

Soekris net4501 with AMD Elan sc520 cpu which has internal time
register resolution of around 100n.

System clock I believe used a TAPR clock-block frequency
synthesizer and a FATpps signal conditioner kits.

I couldn't find any UK supplier for the parts and shipping costs
from the states was too expensive.


David



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