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From: everett@hpcvra.cv.hp.com.CV.HP.COM (Everett Kaser)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Increasing #task switches per second (> 18.2), help
Message-ID: <31600011@hpcvra.cv.hp.com.CV.HP.COM>
Date: 12 Dec 90 23:50:51 GMT
References: <4348@dnlunx.pttrnl.nl>
Organization: Hewlett-Packard Co., Corvallis, OR, USA
Lines: 33

/ levericw@cheetah.ece.clarkson.edu (Walden Leverich) writes...
 > bomgard@iuvax.cs.indiana.edu (Tim Bomgardner) writes:
>Tim> filetp@dnlunx.pttrnl.nl (Peter Filet) writes:
>Tim> >I am developing an Operating System, in the Protected Mode of the i286
>Tim> >processor.
>Tim> > (wants a faster system clock)

>Tim> want, say, a 4X clock rate (72.8/sec), you call the original handler every
>Tim> fourth tick.  The rest of the OS has no idea anything has
>Tim> changed.....

>Very interesting. But wrong.  Considering that your interrupt timer
>will be called once every 1/18.2 seconds. Now if your pass that tick
>onto the OS every fouth time, then the OS gets 1/4 of the clock *NOT*
>4X the clock.

It WILL work,  what was left out of the explanation is this:  after you take
over the interrupt vector, you have to reprogram the timer to interrupt
4 times as often.  THEN, you only pass every fourth one on to the regular
interrupt service routine, maintaining the original frequency for the original
interrupt service routine, but quadrupling the frequency for yourself.

>Tim> Academic types can usually tell you why you can't do something.
>Tim> Commercial software developers can usually tell you how to do it
>Tim> anyway :)

>Academic types in the CompEng field will explain why it is impossible.

NEVER say never! (or impossible)

Everett Kaser                   Hewlett-Packard Company
...hplabs!hp-pcd!everett        work: (503) 750-3569   Corvallis, Oregon
everett%hpcvra@hplabs.hp.com    home: (503) 928-5259   Albany, Oregon