> > timer - it has 16bit counter, and runs 18 times a second
> > when 65535 is used as divider. That gives me 0.84usec precission (good
> > enough). I just wonder how long it takes to do_read_hwtimer()...
>
> It's just a few instructions at assembly level. Windows
> virtual device drivers (oh the horror) have access to a
> function which returns a 64 bit count of roughly 0.8 usec
> intervals since boot. It's nothing more than current timer
> contents + (divider * overflows since boot). Implementing
> a delay wouldn't require anywhere near as much, you just need
> to be a little careful if the current value plus delay wraps.
reading that old ISA timer is awfully slow: at least 3 in/out instructions,
usually 5-6 due to in_p/out_p which is 4-7.6 usec or 1600-3100 cycles
on my PC!.
Harald
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