how does the cpu know if an interrupt is defined? 
Author Message
 how does the cpu know if an interrupt is defined?

I was wondering how the cpu can tell if an interrupt entry in the interrupt
vector table is defined or undefined.
Does it assume its undefined if it is zero?
The interrupts reserved by intel for overflow, div by zero and so on, what
are they suposed to be if there is no handler for them? Leaving a random
value would just make the cpu crash in odd ways, so there must be a
signature for undefined, right?
If no handler is set for div by zero and such an event occures, then what
happens? nothing? It is simply ignored and the cpu will go on putting  a
wierd result into the result register of the division?


Sun, 26 Jun 2005 15:01:11 GMT  
 how does the cpu know if an interrupt is defined?

Quote:

> I was wondering how the cpu can tell if an interrupt entry in the
interrupt
> vector table is defined or undefined.

The CPU cannot tell if a handler is valid. It just executes what's pointed
to by the vector.

Quote:
> Does it assume its undefined if it is zero?

The only time this is true is in protected mode, when the selector is zero,
in which case it throws a GPF.

Quote:
> The interrupts reserved by intel for overflow, div by zero and so on, what
> are they suposed to be if there is no handler for them? Leaving a random
> value would just make the cpu crash in odd ways, so there must be a
> signature for undefined, right?
> If no handler is set for div by zero and such an event occures, then what
> happens? nothing? It is simply ignored and the cpu will go on putting  a
> wierd result into the result register of the division?

Nope. If the handler is invalid, the system will most likely crash and
possibly burn.


Sun, 26 Jun 2005 19:16:12 GMT  
 
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