Re: Autovector exceptions on Atari ST

[Joshua Juran <jjuran@gmail.com>]

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.
>>
>
> Hi Geert,
>
> 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.  Although 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.

Josh