[time-nuts] Designing an embedded precision GPS time

Attila Kinali attila at kinali.ch
Wed Nov 1 08:39:04 EDT 2017


On Tue, 31 Oct 2017 22:13:01 -0700
Denny Page <denny at cococafe.com> wrote:

> Depends upon the results you are trying to achieve. Using Linux pretty
> much guarantees that your server clock will be off by 6-10us, with
> substantial variance. Even with a good nic that supports hardware
> timestamping, the variance will increase substantially as you go off box
> (spread spectrum is a big annoyance!).

6-10┬Ás is the interrupt latency of linux on ARM SoC. I guess, to get
below that you'd have to tweak the kernel a bit. Which should not
be that difficult. Definitly simpler than writing your own IP and NTP
stack from scratch.

Spread spectrum can usually be switched off, though requires at least a
custom DTB or even patching of the kernel. There are a few boards, though
that do not allow spread spectrum to be switched off.

			Attila Kinali


-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson


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