Date:	Thu, 10 Sep 1998 20:22:59 +0300 (IDT)
From:	Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To:	Tal Lavi <ranla AT post DOT tau DOT ac DOT il>
cc:	djgpp AT delorie DOT com
Subject:	Re: Making a keyboard handler
In-Reply-To:	<35F805F1.6D65@post.tau.ac.il>
Message-ID:	<Pine.SUN.3.91.980910201547.10176B-100000@is>
MIME-Version:	1.0

On Thu, 10 Sep 1998, Tal Lavi wrote:

> For the time being, using he getch, gives me a little side-effect.

If you need to support several keys pressed at the same time, you have no 
other way but to install a hardware interrupt handler.  Neither DOS 
(`getch' calls DOS) nor BIOS will support that.

> 1)If I took control on the keyboard hardware interrupt, but I want some
> of the keys to be acknowledged to the old one, there is a port number
> that I don't remember, right?
> should I write the keyboard codes into it?

No, you need to chain (i.e. jump) to the old handler whose address you 
query at startup by calling __dpmi_get_protected_mode_interrupt_vector.

> 2)if the keyboard interrupt is a hardware one, how can it be that it has
> an address in memory?

The interrupt doesn't have an address, only the handler (which is a piece 
of code) does.

> 3)how do I compile ASM files into .S(excuse my ignorance)?

.S files *are* assembly language sources.  You compile them into object 
files as usual, by calling GCC:

	gcc -c foo.S

> 4)how will I link those .S files into my program?

You link object files, not source files.  The above command will produce 
a file foo.o which you then link as usual.

> 5)how will I be able to use the keyboard variable declared in my main c
> source, in the handler, that was written somewhere else?

You need to declare your assembly function as a public function, then the 
linker will resolve the references to it.

I suggest to take a look at the Allegro library, which has several 
hardware interrupt handlers, including for the keyboard.  You can see 
there several examples of how this is done.

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