From:	"Miles F. Bintz Ii" <bintzimf AT clarkson DOT edu>
Newsgroups:	comp.os.msdos.djgpp
Subject:	More interrupt handling questions
Date:	Mon, 19 Oct 1998 12:45:11 -0400
Organization:	Clarkson Univeristy
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

Just to verify, if I wanted to write an ISR  for IRQ 4, I would install it
into vector 0x0c, correct (in DPMI)?

Here's a brief history....

I have a PCI device whose interrupt line is 0 on bootup.  I manually set
this to IRQ 4 in the config space and then tell the card that its OK to
start issuing interrupts.

Heres the routine that installs the handler....

void ISR() {
    disable();
    interrupt_count++;

    /* can I call this in my ISR or does this end up being 
       a far call?
     */
    _farpeekl(yadda, yadda)

    /* Signal EOI: do I need to do this? */
    outportb(0x20, 0x20);
    enable();
}

void endof_ISR() {}

void install_handler() {
    .
    .
    .

    read_cfg_space(0x3c, &i);
    write_cfg_space(0x3c, (i & 0xffffff00) | 0x4, LONG);
    newISR.pm_offset = (int) ISR;
    newISR.pm_selector = _go32_my_cs();
    _go32_dpmi_lock_data(&interrupt_count, sizeof(interrupt_count));
    _go32_dpmi_lock_data(&interrupt_code, sizeof(interrupt_count));
    _go32_dpmi_lock_code(ISR, (long) endof_ISR - (long) ISR);
    _go32_dpmi_get_protected_mode_interrupt_vector(
       0x0c, &oldISR);
    _go32_dpmi_allocate_iret_wrapper(&newISR);
    _go32_dpmi_set_protected_mode_interrupt_vector(
       0x0c, &newISR);

    /* still working at this point */
    .
    .
    .
    tell_hardware_ok_to_int();

    /* frozen */

}

So thats that.  The problem is, whenever the hardware starts issuing
interrupts, the computer locks up.  No mouse, no keyboard, but my
softpower till works.  The frequency of these interrutps should be about
60-85 Hz as this is the vertical retrace interrupt generated by a graphics
adapter.

I dont have any idea why this isn't working.  I've read the DPMI spec, the
DJGPP FAQ, and some of the Allegro stuff...  The routines above are almost
identical to those found at
   
   http://www.abwillms.demon.co.uk/prog/djints.txt

Some other tidbits: I realize that the wrapper isn't locked in memory, but
I don't believe the system is paging.  I'm currently running under win95,
but I
think there is still plenty o' memory available.  The same things happen
when I run with cwsdpmi.


A pre-emptive thanks for your help/suggestions!

-Miles

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