On 13/11/2019 18:46, druck wrote:
> On 13/11/2019 12:11, Areligious Republican wrote:
>> 1. Out of interest, were there to be a 32 bit application
>> running under a 64 bit OS, what actually happens when an
>> interrupt comes along, andinterrupt that might have system-wide
>> importance?
>>
>> Is it dealt with by the 32 bit IRQ / FIRQ mechanism or does
>> it switch back to the 64 bit?
>
> The interrupt (or any other exception) causes a 64 bit privileged mode
> to be entered, and is handled by the 64 bit OS. On exit it may return to
> the 32 bit non-privileged mode the application is running in.

That's what I thought which was why I could not see any need for the 32
bit IRQ/FIRQ processing (Actually, answering my own question, it's for
when the whole caboodle is running in 32 bit mode)

>
> Incidentally, it is also possible on the A53 to run 32 bit OS along side
> a 64 bit OS using a 64 bit hypervisor. In that case the hypervisor
> decides which OS the interrupt or exception should be handled by, and
> either passes it to the 64 bit OS, or invokes the 32 bit mode's IRQ/FIRQ
> handlers.

Yes, and I've yet to read up on the GIC distributing the interrupts.

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