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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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.

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

Chris