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List:       bochs-dev
Subject:    Re: [Bochs-developers] Pic Priorities, polled and autoeoi
From:       Jonathan Hunt <jhuntnz () users ! sourceforge ! net>
Date:       2001-11-25 3:28:51
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On Sat, 24 Nov 2001 22:47, Dave Poirier wrote:
> > Oh and while I'm at it if there is anything else in pic model that needs
> > improving/implementing please let me know. I may as well finish what I
> > started.
> >
> > Jonathan Hunt
>
> Thanks for the patch, I'm sure it will help in many places.  Thinking of
> it, there is one model that isn't exactly right in the current pic
> implementation.
>
> When an IRQ is masked and the device raises an IRQ, the real PIC will
> set some bit inside to indicate to trigger an INT for this IRQ when it
> is unmasked.  If a Specific-EOI is sent to the PIC for this IRQ while it
> is still masked, the PIC will clear the bit indicating to raise an INT
> when the IRQ will be unmasked.
>
> The current implementation, AFAIK, doesn't clear this INT request.
>
> I'll try your patch on my os and see if everything still behave
> properly. Later :)
>
> EKS - Dave Poirier

I'm afraid I don't understand quite what you mean. A specific eoi clears the 
isr and irr bits for that interrupt regardless of whether or not the 
interrupt is enabled (at least that's what I think it does). Here is what I 
think happens:

1 - irr bit is set and service_*_pic is called.
2 - since bit is masked nothing happens
3 - specific eoi command is sent irr bit is cleared and service_*_pic is 
called again. Nothing happens again.
4 - bit is unmasked and interrupt is now enabled but since irr bit is cleared 
nothing happens until it is set again (by another interrupt request).

Are you saying that it goes ahead and raises an interrupt when it shouldn't 
in step 4? Or am I totally off about what you mean? I'd be happy to do it 
once I figure out what you mean (last day of exams are tomorrow so more time 
then).

Jonathan Hunt 

-- 
Jonathan Hunt (The Real Jonathan Hunt) <jhuntnz@users.sf.net>
Jabber at jhuntnz@jabber.com
"He is no fool who gives what he cannot keep to gain what he cannot lose." 
Jim Elliot

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