Date:	Mon, 10 Apr 2000 19:45:23 +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.3.91.1000410084111.19649G@is>
Message-ID:	<Pine.LNX.4.10.10004101933460.1286-100000@darkstar.grendel.net>
MIME-Version:	1.0
Reply-To:	djgpp AT delorie DOT com
Errors-To:	nobody AT delorie DOT com
X-Mailing-List:	djgpp AT delorie DOT com
X-Unsubscribes-To:	listserv AT delorie DOT com

On Mon, 10 Apr 2000, Eli Zaretskii wrote:

> 
> On Sun, 9 Apr 2000, Kalum Somaratna aka Grendel wrote:
> 
> > 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.
> 
> No, it won't, at least not with all DPMI providers.
> 
> A real-mode handler helps to avoid the overhead of the reflection from
> real to protected mode, which happens when the interrupt is raised
> while the CPU is in real mode (e.g., inside a DOS call), while the
> handler is a protected-mode one.
> 
> However, in this case, we have the opposite situation: the handler is
> a real-mode one (a real-mode TSR), while the CPU stays in protected
> mode most of the time because a DJGPP program runs in the foreground.
> A real-mode handler worn't help here, since most DPMI servers will
> call the protected-mode handler first, and only then reflect to the
> real mode.

Hmm.... I was commenting on a generic protected mode program that has to
do com port handling.

Would it be possible then for him to rewrite the 16-bit TSR as a
protected mode TSR  with a real mode handler too..then wouldn't that avoid
the problem...

Grendel

Hi, I'm a signature virus. plz set me as your signature and help me spread
:)

- Raw text -