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From: Luigi Rizzo <luigi@labinfo.iet.unipi.it>
Message-Id: <199711071648.RAA27137@labinfo.iet.unipi.it>
Subject: Re: Inter outb() timing
To: jamil@trojanhorse.ml.org (Jamil J. Weatherbee)
Date: Fri, 7 Nov 1997 17:48:07 +0100 (MET)
Cc: hackers@FreeBSD.ORG
In-Reply-To: <Pine.BSF.3.96.971107091323.184A-100000@trojanhorse.ml.org> from "Jamil J. Weatherbee" at Nov 7, 97 09:16:23 am
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> If I do a:
> 
>    outb (0x300, 0x00);
>    outb (0x300, 0xff);
>    outb (0x300, 0x00);
> 
> How long should 0xff appear at that address?

assuming that:
- your process is not pre-empted in the middle of the sequence;
- you don't get a page fault before the last instruction;
- your processor is fast enough that reading the next instruction
  does not cause stalls (yes there are still 386sx-16 serving us...) ;

then probably the time depends on the configuration of the ISA bus
on your machine (clock, wait states), and you might observe a time
in the 200..800ns range.

	Cheers
	Luigi