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Subject: Re: Using outportb() with djgpp
Date: Sat, 12 Jul 2014 10:38:00 +0200
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Reply-To: djgpp AT delorie DOT com

"Mateusz Viste" <mateusz DOT viste AT delorie DOT com> wrote:

> And NOW my seemingly random reboots suddenly make a lot of sense! :) But 
> I am unable to explain why running under real mode would mask reboots, 
> as the ACPI vs MPU401 conflict shall be present both in real and 
> protected modes...    So many roads.

Maybe it has something to do with how you issue the EOI command
to the master and/or master PIC?

When I did such things for a Digiboard PC/x (an 8-channel RS-485 board) 
under DOS/turbo-C, there had to be a "specific EOI" to the master PIC. 
Like:
    outportb (0x20, 0x60 | asyncCnf[port].irq); 

which AFAICR gave different results than a "non-specific EOI":
    outportb (0x20, 0x20);     

(I seems to remember I lost input data when I did that).

Not only that, but if your IRQ was hooked to the slave PIC, the 
"specific EOI" must be issued to the slave PIC first:

  if (com->int_vect >= 0x70)
     outportb (0xA0, 0x60 | asyncCnf[port].irq);  
  outportb (0x20, 0x60 | asyncCnf[port].irq);

Hope you get the idea; it's been 10 years since I coded such things.

--gv