[ntp:questions] Re: ntpd transmit timestamp precision
David L. Mills
mills at udel.edu
Tue Feb 14 13:43:58 UTC 2006
THe ntpd in ntp-dev has been run in simulation with tick = 10 ms and
done amazingly well. The low order nonsignificant bits are se to a
random fuzz that apparently averages out just fine.
Damion de Soto wrote:
> Brian Utterback wrote:
>> Yes and no. If your system supports either clock_gettime or getclock,
>> then the code does not bother with the random bitstring, since there
>> are only two unused bits to set. Not worth the trouble.
> Thanks, but I have a system here that has very low resolution system clock,
> ntpd correctly detects this via default_get_precision() as:
> Feb 13 07:01:31 ntpd: precision = 10000.000 usec
> I have clock_gettime() available to me, but the nanoseconds values will
> be mostly wrong, since 10ms only gives me 7 bits of precision.
> This means all 64bits of the fractional seconds in the Transmit
> Timestamp are nearly always the same.
> Has no-one else ever run into this before?
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