From: "Mark Usher" <marku AT magnet DOT at>
Newsgroups: comp.os.msdos.djgpp
Subject: Enabling a specific interrupt
Date: Sat, 5 Jun 1999 20:31:16 +0200
Organization: Telenor magnet GmbH
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

Hi

I am writing directly to the PIC to check if an interrupt is enabled with
the following code. If the interrupt is not enabled then I enable it.
Two questions.
1) Is there any easier / eleganter way to do this
2) Should I install the handler for this interrupt before or after this
routine.

Mark Usher
marku AT magnet DOT at

#define CARD_INTERRUPT    0x07
#define SPECIFIC_EOI            0x60

byte CheckInterrupt(void)
{
    byte value;
    byte mask;
    byte i;

    mask = 0x01 << CARD_INTERRUPT;

    /* test to see if the interrupt is in use */
    asm ("cli");

    value = CARD_INTERRUPT | SPECIFIC_EOI;
    outportb(0x20, value);        /* OCW 2 */

    i=0;
    do
    {
        /* Select IRR Interrupt Request Register */
        outportb(0x20, 0x10);        /* OCW 3 */
        i++;
        value = inportb(0x20) & mask;
    }
    while ((i<255) && (value ==0));

    if (i>=255)
    {
       printf("Interrupt already in use. 0x%X\n",value);
       return -1;
    }

    value = CARD_INTERRUPT | SPECIFIC_EOI;
    outportb(0x20, value);        /* OCW 2 */

    /* enable the cards interrupt */

    value =inportb(0x21);
    value = value & ~(0x1 << CARD_INTERRUPT);  /* Set the mask for the PIC
command */
    outportb(0x21, value);

    return 0;
}