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From:	"Jordar" <rrcdaniel AT sbcglobal DOT net>
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Subject:	Re: porting from borland
Date:	6 Nov 2006 09:54:34 -0800
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DJ Delorie wrote:
> The only thing I can think of is to set up your handler first, then
> enable interrupts.  The BIOS's default handler may be disabling
> "rogue" interrupts.
>
> Are you installing both a PM and RM handler?

I do install the handler first.... below is code for setting up
interrupt 1-7:
void InitHostIT(void interrupt (*IntVect) (void), short IRQNum)
{
 unsigned char IMR;
disable();                           // Don't want short called during
revector
outportb(0x20, 0x20);         //  acknowledge any pending IRQ
_go32_dpmi_get_protected_mode_interrupt_vector(IRQNum, &old_handler);
new_handler.pm_offset = (unsigned long) IntVect;
new_handler.pm_selector = _go32_my_cs();
_go32_dpmi_allocate_iret_wrapper(&new_handler);
_go32_dpmi_set_protected_mode_interrupt_vector(IRQNum, &new_handler);
IMR = inportb(0x21);               // Read in current IMR
IMR &= ~(1 << IRQNum);             // Clear desired bit
outportb(0x21, IMR);               // Out new IMR
enable();
}

I think you are definately on to something.  If I read back the value
of the pic before the enable(), it returns the proper value.  However
if I do the same thing immediately after the enable the PIC returns
back with the interrupt disabled.  Something (BIOS??) is disabling it
so I must not be setting up the Handler properly.

I am using the above PM handler code only.  Perhaps I need to
experiment with a RM handler or is there something else missing to the
above?  

Thanks for your help

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