Re: [Qemu-devel] [PATCH v4 5/5] i8259: fix dynamically masking slave IRQs with IMR register

[Avi Kivity]

On 09/03/2012 07:02 PM, Jan Kiszka wrote:

>>>> Looks like the optimal condition is ((s->icw3 & ~s->eclr) != 0) (i.e.
>>>> bit set in icw3 but clear in eclr).
>>>
>>> The standard PC values are optimal: 4 for master, 2 for slave.
>> 
>> Can you explain why?  I saw that icw3 is always ORed with eclr, so my
>> condition will catch exactly those cases where a change in behaviour
>> occurs, and no more.
> 
> The values above are what every user of the PIC cascaded on our targets
> must program to use them. So We will find them in the state once any
> relevant guest code was able to run (e.g. the BIOS).
> 

Suppose the bios has not run yet?


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