From:	Serge Golovin <res AT marstu DOT mari DOT su>
Message-Id:	<199701131202.PAA03194@marstu.mari.su>
Subject:	Re: Low-level access
To:	mmastrac AT acs DOT ucalgary DOT ca (Matthew Mastracci)
Date:	Mon, 13 Jan 1997 15:02:40 +0300 (MSK)
Cc:	djgpp AT delorie DOT com (DJGPP Mailing List)
In-Reply-To:	<Pine.A41.3.94.970112005041.31292A-100000@acs2.acs.ucalgary.ca> from "Matthew Mastracci" at "Jan 12, 97 00:57:48 am"
MIME-Version:	1.0

Matthew Mastracci wrote:
> From my understanding,
> any program not running at ring-0 invokes an exception error with port
> I/O? 
Wrong. It completely depends on your PM manager and how it sets up port I/O
map. If PM needs to control certain ports it will set proper bits in this
map and you'll get exceptions. If not - you'll run clear.
Yes, there is additional overhead in processing your in and out instructions
while you're in protected mode. But this is "hardware" overhead. Processor
has to check I/O map everytime it does in/out. This promlem slightly solved
by chaching TS segments, ehich is done in majority of processors.
> I believe I know the fastest way to to access my graphics memory,
> but as I'll be needing the port accesses to go hand-in-hand with the
> memory accesses, I'd like to know the fastest way to do it.  Thanks in
> advance,
What _exactly_ aree you trying to do?
-- 
SerGo, aka RES

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