MPC8xx: resolution of gettimeofday() ?

[Steven Scholz]

Hi all,

what is the resolution of gettimeofday() for an MPC8xx?

IIUC then the "decrementer" is used to generate the timer interrupts every 10ms.

This decrementer runs at cpuclk/16. Thus with 80MHz CPU clock has a
resolution of 16/80MHz = 200ns and overflows every 50000 ticks.

But is this decrementer used to update xtime?
Will gettimeofday() have a resolution of 200ns?

How about linux 2.4 where xtime is a "struct timeval" rather then "struct
timespec"?

This trivial test programm

        struct timeval first, next;
        double diff;

        gettimeofday(&first, NULL);
        do {
                gettimeofday(&next, NULL);
        } while (first.tv_usec == next.tv_usec &&
                 first.tv_sec == next.tv_sec);

        diff  = ((double)  next.tv_sec - (double) first.tv_sec) * 1e6;
        diff +=  (double) (next.tv_usec - first.tv_usec);

        printf ("Resolution gettimeofday() = %g ?s\n", diff);

says it's between 13 - 16 ?s on a linux-2.4.20. Could that be? how does this
relate to the decrementer frequency?

Thanks a million!

--
Steven