is the resolution of do_gettimeofday in usec?

Hi All,
i have board that contains MPC8555 processor with linux 2.6.27 ported to it.
i want to use an accurate function to measure the time. i searched the
kernel code & i found several functions but i read that the do_gettimeofday
is the most accurate one since it has a timer resolution of usec.

my question is how this function give this accuracy while the kernel timer
is 4msec?
is this a real accuracy or does it convert from msec to usec?
or does it depend on another timer counter that has this resolution?
or may b it measure the clock cycles of the processor within certain
interval?

Note that the freq of the processor is 850MHz.

Unfortunately, the function is implemented in assembly & i cant understand
it?
so can u tell me how this accurate numbers can be got or they r just fake
numbers?

thanks
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wael showair wrote:

Hi All,
i have board that contains MPC8555 processor with linux 2.6.27 ported to it.
i want to use an accurate function to measure the time. i searched the
kernel code & i found several functions but i read that the do_gettimeofday
is the most accurate one since it has a timer resolution of usec.

You might also look at clock_gettime(), which has a theoretical accuracy
of nanoseconds.  Both this and gettimeofday are NTP-corrected if you are
synced to an NTP clock.

my question is how this function give this accuracy while the kernel timer
is 4msec?

The accuracy of the timestamp is not related to the tick interval.

Chris