Re: Autovector exceptions on Atari ST

[Greg Ungerer <gerg@snapgear.com>]

On 25/08/11 18:13, Geert Uytterhoeven wrote:
> On Thu, Aug 25, 2011 at 03:51, Joshua Juran<jjuran@gmail.com>  wrote:
>> On Aug 24, 2011, at 12:47 PM, Matthias Reis wrote:
>>
>>>> On Sun, Aug 7, 2011 at 23:09, Geert Uytterhoeven<geert@linux-m68k.org>
>>>> wrote:
>>>>
>>>> MFP interrupts are not autovector interrupts, but user vector interrupts.
>>>>
>>>> Sorry, I forgot about this: it may be a stack frame format issue,
>>>> which causes the kernel to
>>>> incorrectly identify the interrupt number.
>>>>
>>>> user_inthandler() in arch/m68k/kernel/entry_mm.S looks at the
>>>> PT_OFF_FORMATVEC
>>>> field in the stack frame to identify the interrupt source. I don't
>>>> know from memory
>>>> if the plain 68000 stores it there. For autovector interrupts, it
>>>> doesn't, that's why
>>>> I created inidividual auto*_inthandler() functions that put an hardcoded
>>>> number
>>>> on the stack instead of looking at the stack frame.
>>>
>>> thanks for your kind reply. As far as I understand the 68000 manual
>>> (http://www.freescale.com/files/archives/doc/ref_manual/M68000PRM.pdf,
>>> section b.2), the CPU does not store the vector number on the exception
>>> stack. This is also what I've seen in the debugger: some seemingly bogus
>>> irq number is passed to m68k_handle_int. Any suggestions how to solve
>>> this? I guess it is not a good idea to write an individual
>>> user*_inthandler for each of the 255-64=191 possible user interrupts.
>>
>> It's not out of the question. áAlthough you wouldn't write 192 little
>> functions by hand -- just have stubs that push the vector number or offset
>> onto the stack and branch to another function, and generate the stub code at
>> runtime.
>
> And you only have to do it for the user interrupts you actually need/use.

That is pretty much what the code for the 68328 does.

   arch/m68k/platform/68328/entry.S

It has 8 handlers for the 8 real interrupts it can handle.

Regards
Greg


> I.e. m68k_setup_user_interrupt() could allocate the needed memory and fill
> it with the generated interrupt handlers.
> For Atari that's doable, for VME it would still generate all 192 of them.
> Alternatively, let m68k_irq_startup() handle it when it's called the
> first time for
> that specific interrupt.