L4-Linux worked on 486!

[edmundo at rano.demon.co.uk]

> >It dies after saying "irq still active".
> >(To get that message I'm using the patch that Michael Hohmuth
> > posted to the list on July 25.)
> > I think I may have found a bug in the SANITY code in
> > linux22/arch/l4-i386/kernel/irq.c, by the way. See below.
> 
> I remember, I've ever seen same message & following crash,
> thanks for the patch.

Unfortunately I still don't understand why the irq is "still active".

Here's the corresponding bit of code in irq.c. (The lines which aren't
indented as much as they should be came from Michael's debugging
patch.)


  mask = 1 << (irq & 7);
  if (irq < 8)
    {
      outb(inb(0x21) | mask, 0x21);	/* block the irq */
      outb(0x20, 0x20);	/* acknowledge the irq */

outb(0x0B, 0x20);
if (inb(0x20) & mask)
  enter_kdebug("irq still active");
    }
  else 
    {
unsigned foo;

      outb(inb(0xA1) | mask, 0xA1);	/* block */
      outb(0x20, 0xA0);	/* acknowledge */
      outb(0x0B, 0xA0);
      if ((foo = inb(0xA0)) == 0)
	outb(0x20, 0x20);
if (foo & mask)
  enter_kdebug("irqslave still active");

    }      


If you look at the bottom of kernel/fiasco/src/irq.h you'll find an
unused function irq_ack() which does roughly the same thing, because
acknowleding the IRQ is something that ought to be done by L4/Fiasco,
but is at present done by Linux.

So why do we get "irq still active" during heavy use of the network
card? Is there a PIC expert in the house?

Is it possible that the problem is caused by the interrupt not being
acknowledged quickly enough? If so, maybe I should move the ack from
Linux into Fiasco ...

Edmund