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From: saify@cbnewsl.ATT.COM (saify.lanewala)
Newsgroups: comp.sys.ibm.pc
Subject: Re: .84 usec Timer resolution on PC
Summary: jmp $+2 instruction
Message-ID: <3056@cbnewsl.ATT.COM>
Date: 28 Nov 89 20:44:53 GMT
References: <25235@sequent.UUCP> <1757@crdos1.crd.ge.COM>
Distribution: usa
Organization: AT&T Bell Laboratories
Lines: 30

In article <1757@crdos1.crd.ge.COM>, davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr) writes:
> In article <25235@sequent.UUCP> norsk@sequent.UUCP (Doug Thompson) writes:
> 
> | To program Timer 0 to Mode 2 do the following:
> | 
> | 	jmp 	$+2
> 
>   Could you explain the "jmp $+2" instructions? I mean, I know what they
> do, but not why you're doing it. If this is supposed to be a software
> 
> -- 
> bill davidsen	(davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen)
> "The world is filled with fools. They blindly follow their so-called
> 'reason' in the face of the church and common sense. Any fool can see
> that the world is flat!" - anon

That instruction is intended to flush the pre-fetch queue.  I read that
somewhere, but cannot give more insight.  Perhaps some hardware guru .....

There's an article in Programmer's Journal of last month (I believe) that
describes in detail an implementation of a fast timer for use in doing
performance measurements of small sections of graphics code.

There's also information on the jmp $+2 instruction in that article,
if you're interested.

Good luck.

Saify Lanewala
....attunix!stl