[ntp:questions] Loopstats jitter field mostly zero?

David Taylor david-taylor at blueyonder.co.uk.invalid
Tue Jan 8 10:16:33 UTC 2013

On 07/01/2013 22:32, Harlan Stenn wrote:
> David Taylor writes:
>> On 14/12/2012 08:17, David Taylor wrote:
>>> Reported as bug 2314:
>>>     http://bugs.ntp.org/show_bug.cgi?id=2314
>> There's been no at all progress with this bug report.  ...
> My focus is on bugs that are blocking the 4.2.8 release.
> The logged value looks like clock_jitter to me, and that's initialized
> to LOGTOD(sys_precision), and it gets updated at lines 413 and 583/585
> of ntp_loopfilter.c .
> H

Thanks, Harlan.  I see that a function SQRT() is used, and that this 
function is defined as sqrt() in ntp.h:

   #define SQRT(x) (sqrt(x))

I recall seeing /something/ about hardware and software floating point 
support in the Raspberry Pi, that some hardware/firmware/software had it 
and some not.  I wonder whether that might be the cause?  I can't 
imagine sqrt() being broken, but maybe for very small numbers it's 
wrongly returning zero?  Single precision versus double precision?  As 
you know, I'm well out of my depth on this, but could there be a 
configuration flag to use software FP rather than hardware?  I wonder 
how best to go about solving this problem?

This may be completely the wrong track, of course...
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