Real-Time Granularity: A Query

[Chris Torek]

In article <598 at codonics.COM> bret at codonics.COM (Bret Orsburn) writes:
>The gettimeofday function returns (in part) a microsecond resolution counter.
>The docs I have found so far indicate that this counter is really just bumped
>by the system tick interrupt at a 50-100 HZ rate. Is that a useful
>generalization? Are there any significant counter-examples?

No, and yes (in that order): 4.3BSD on most VAXen, for instance.  These
have a 100 hz clock, but can read the countdown (acutally count-up) register
to tell how long it has been since the last clock interrupt, and there
is a routine called microtime() that calculates the time to the nearest
microsecond or so.  Of course, by the time the time has been calculated,
it is wrong again. . . .
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris at cs.umd.edu	Path:	uunet!mimsy!chris