[ntp:questions] NTP on CubieBoard

Rob nomail at example.com
Mon Oct 13 14:35:29 UTC 2014


David Woolley <david at ex.djwhome.demon.invalid> wrote:
> On 13/10/14 09:23, Rob wrote:
>> On the PC platform, with a recent development ntpd I can achieve
>> PPS sync with offset within a couple of us on systems in normal
>> environment, and well within 1us in a temperature conditioned room.
>
> The correct quality measure is jitter, rather than offset.  offset 
> varies from sample to sample but still doesn't tell you the systematic 
> error in the time.

I know that, the jitter is well below 1us on our systems.  But we
require small offset as well.

My point is not to discuss the requirement and viability of good time
accuracy on ntpd.  I know I can achieve what I need on a PC.

My question is if it can be done on a Cubieboard2.  I think one of
the key requirements is the availability of a high-res (nanosecond)
timer that can timestamp the PPS events and serves as a system
realtime clock.  Not a 10ms interrupt driven realtime counter, as some
systems have.

Another is the availability of a programmable input bit that can issue
a processor interrupt that will be rapidly served.  That means the system
must not spend long time with interrupts disabled or at such a high
load that it cannot perform quick actions.

Our application should leave plenty of headroom on the 2 x 1GHz ARM-7
processor.  So my question is if the other requirements are fulfilled,
preferably on a default Linux install (Cubian).



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