[ntp:questions] Re: ntpd transmit timestamp precision

Damion de Soto damion at cyberguard.com.au
Thu Feb 16 04:43:28 UTC 2006


Hi Brian, Danny, David.

So, currently the low-order bits are only randomised if the system doesn't
have HAVE_CLOCK_GETTIME || HAVE_GETCLOCK.
They should always be randomised to the calculated precision of the system.
(incidently, in the two libraries i've just looked in - glibc & uClibc - the 
clock_gettime() function just calls gettimeofday() anyway - so they definately 
shouldn't be treated differently)

I tried to work out an easy way to always add random fuzz to our current degree of 
system precision, but then i ran into the second problem:

the system clock precision is calculated in default_get_precision() in ntp_proto.c  - 
this function uses consecutive calls to get_systime() to calculate the  minimum tick 
difference.  Won't this be always wrong if the random fuzz code in get_systime() is 
used, and give a much higher precision than is really available?

regards,

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