From: Gregg Roe <groe AT magsep DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Hooking a parallel port interrupt
Date: Thu, 25 May 2000 09:51:44 -0500
Organization: MSS, Inc.
Lines: 43
Message-ID: <392D3E00.15DFD7FB@magsep.com>
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

I'm trying to execute a C procedure when an interrupt on a Lava parallel
PCI board is received. The following code does hook the interrupt, but
then crashes. This occurs whether memory is locked or not. If I change
the code to use the built-in parallel port, it doesn't work at all. Any
suggestions or sample code would be appreciated.

Gregg Roe
MSS, Inc.


void int_test()
{
    gTemp++;
    outportb(PIC,0x20);
}

// *** Initialize the external interrupt
void init_ext_int()
{
    _go32_dpmi_seginfo oldh, newh;

    // put port in forward direction
    outportb( PARCONT, inportb( PARCONT) & 0xDF);
    // write data to port
    outportb( PARDATA, 0xAA);
    // lock test function and variable
    LOCK_FUNCTION(int_test);
    LOCK_VARIABLE(gTemp);
    // get the old handler info
    _go32_dpmi_get_protected_mode_interrupt_vector( PARIRQ, &oldh);
    // set new handler info
    newh.pm_offset = (int)int_test;
    newh.pm_selector = _go32_my_cs();
    // get the wrapper
    _go32_dpmi_allocate_iret_wrapper( &newh);
    // make it the new interrupt handler
    _go32_dpmi_set_protected_mode_interrupt_vector( PARIRQ, &newh);

    // unmask PIC
    outportb( PIC+1, inportb( PIC+1) & 0xEF);
    // set IRQ enable bit on port
    outportb( PARCONT, inportb( PARCONT) | 0x10);
}