Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!codonics!bret
From: bret@codonics.COM (Bret Orsburn)
Newsgroups: comp.unix.wizards
Subject: Real-Time Granularity: A Query
Message-ID: <598@codonics.COM>
Date: 13 Dec 89 20:28:27 GMT
Reply-To: bret@codonics.com (Bret Orsburn)
Organization: Codonics, Inc., Middleburg Heights, OH
Lines: 26

Here is a question for the Unix Wizards (Any of you left out there? :-)

How coarse is the real-time base on *real* Unix machines?

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?

Some context:

I am contributing to the design of a stand-alone system that will run some
code ported from a Unix environment. This code uses the gettimeofday system
call to derive a millisecond-resolution timestamp.

If *real* Unix just bumps this counter 50-100 times per second, I can
immediately recommend that behavior as a minimum system capability. I can
then take steps to determine if there is any real benefit in exceeding this
minimum capability.

TIA, Wizards.
-- 
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bret@codonics.com
uunet!codonics!bret
Bret Orsburn