Date:	Mon, 27 Feb 1995 14:19:16 +0500
From:	hvb AT netrix DOT com
To:	THE MASKED PROGRAMMER <badcoe AT bsa DOT bris DOT ac DOT uk>
Cc:	djgpp AT sun DOT soe DOT clarkson DOT edu
Subject:	Re: One More Confused Interrupt Question
References:	<0098C9C2 DOT 01C1C057 DOT 2 AT bsa DOT bristol DOT ac DOT uk>

THE MASKED PROGRAMMER writes:
 > 
 > (i) What is the difference between a Real Mode interrupt and a Protected Mode
 >     interrupt.
 >
Real mode interrupt relates to the time that the interrupt occurs, the
processor is in real mode.  If you want your protected mode to execute
some of the code at this time you need to hook the protected mode code
to the real mode interrupt.

So I guess you know what is the Protected mode interrupt is.  One
catch is you need to call the DOS interrupt every so often from the
protected mode to keep the DOS clock running.

 > (ii) Why, when I use the example from the documentation (which hooks the clock
 >      tick and uses it to increment a volatile int) does the int seem to
 >      increase (a) erratically and (b) far more slowly that 18.3 times per
 >      second.
 > 
 > (iii) If I use the provided _go32_* functions do they put a lot of overhead
 >       into the interrupt servicing ?
 > 

Yes it does add some overhead but I do not know how much.  I know that
if your clock interrupt uses a lot of processing time, you get some
weird behavior and the system eventually hung.

We actually reprogram the clock to have 1ms interrupt.  It has been
working, however, recently we had one or two system hung problem,
which I guess it is due to this interrupt.

Hope this helps.

Hung.

==============================================================
Hung Bui                            Internet: h DOT bui AT ieee DOT org
Netrix Corporation                    Phone: +1 703 793 1016
13595 Dulles Technology Drive           Fax: +1 703 713 3805
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