Message-ID:	<31983628.7AF2@nuernberg.netsurf.de>
Date:	Tue, 14 May 1996 09:28:40 +0200
From:	Ralf Suessbrich <ralf DOT suessbrich AT nuernberg DOT netsurf DOT de>
Organization:	The Internet
MIME-Version:	1.0
To:	djgpp AT delorie DOT com
Subject:	Interrupt Handler

Hi ;)

I am learning to program on low level. As a first excercise i
decided to program a short interrupt-handler for IRQ2. I wrote
a function wich has an output of an one second durating sound.
I first get the old ivector, then "allocate iret wrapper", then 
i have a test period of 20 seconds, then i restore the old ivector.
 My proggi compiles fine, but when i am running it,
i get only one sound (when i press serveral keys on the keyboard).
After 20 seconds it comes back to a dos prompt, but something went
wrong with restoring the old vector: the keyboard is still out of 
function.

What is my mistake?

Ralf Suessbrich



Here's the code:

#include <dpmi.h>
#include <stdio.h>
#include <dos.h>

keyb_handler () {
    nosound();
    sound (500);
    sleep (1);
    nosound ();
}

main () {
    _go32_dpmi_seginfo old_handler, my_handler;

    printf ("Getting old I-Vector !\n");
    _go32_dpmi_get_protected_mode_interrupt_vector (9, &old_handler);

    my_handler.pm_offset = (int) keyb_handler;
    _go32_dpmi_allocate_iret_wrapper (&my_handler);

    printf("\nSeting new I-Vector !");
    _go32_dpmi_set_protected_mode_interrupt_vector (9, &my_handler);
   
    printf("\nDONE !!\n\nWaiting now 20 seconds for testing.\n");
    sleep (20);
    _go32_dpmi_set_protected_mode_interrupt_vector (9, &old_handler);
   
    printf("\n\nOld I-Vector restored ;)\nEnd");
    return 0;
}

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