Date:	Sun, 9 Apr 2000 19:05:12 +0600 (LKT)
From:	Kalum Somaratna aka Grendel <kalum AT lintux DOT cx>
X-Sender:	root AT darkstar DOT grendel DOT net
To:	djgpp AT delorie DOT com
Subject:	Re: HARDWARE INTERRUPT HANDLING BY CWSDPMI
In-Reply-To:	<Pine.SUN.3.91.1000409084705.7469T-100000@is>
Message-ID:	<Pine.LNX.4.10.10004091901040.1090-100000@darkstar.grendel.net>
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Reply-To:	djgpp AT delorie DOT com
Errors-To:	nobody AT delorie DOT com
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On Sun, 9 Apr 2000, Eli Zaretskii wrote:

> 
> A DJGPP program indeed incurs additional overhead, because under DPMI,
> all hardware interrupts are reflected to protected-mode handlers
> first, and only if unhandled, they are passed to real-mode handlers.
> The mode switch that this involes takes up hundreds of CPU cycles.
> 

In such a case like handling com port interrupts, installing *both* a real
mode and a protected mode handler should avoid this overhead.

Infact I thought that it was standard practice when writing protected mode
programs that handle transmission etc, that a real mode handler should
also be installed to avoid any loss as then if a interrupt occurs in
real mode, it is handled in real mode itself instead of the normal
protected mode switch that taks place.

Grendel

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:)

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