timer resolution of ping programme

I have posted a thread asking details about PING programme. Thanks for all
who answered and read it. There is much more fun discussing with/talking to
others than working alone.But now it's time for some more question on the
PING programme :-P

It is indicated by Stevens' book: TCP Illustrated that BSD implementation
has improved resolution for the timer used in PING programme under it
development. Details below:

BSD/386 version 0.9.4: ping timer resolution millisecond

BSD/386 version 1.0: microsecond.

This leads to a improvement in the ping rtt record: from ms to us...

But: what about later version of BSD? (I have print the rtt on my Freebsd
6.2 box and it seems have the resolution of us as well)
a more important question: does this timer resolution related with the
interrupt rate of the CPU? I actually suspect so, but how?

Thanks for all.

Best wishes,
Xiaochuan