SEVERE Bug in mc68360 _ISR_Handler???

[Chris Johns]

Joel Sherrill wrote:
> 
> Then we are back to my question.  Does the hardware give
> us anything to check to know we have nested?  The separate
> stack m68k's have a throwaway F/VO and we use it.  How about
> the 360?
> 

For the CPU32+ core doco (68360 user manual) I have in section 5.5.2.11
the PC saved is the address of the instruction that would have executed
if the interrupt had not occurred. What if on a CPU32+ (CPU32??) when
you decided to exit the saved PC is check to see if it is _ISR_Handler.
If it is you know you have hit this condition and should just perform an
RTE. Any other address should be covered by incrementing the nesting
counter. It is about the only CPU32(+) generic way I can see of doing
this.

An old 68000 manual states this is also true. Maybe all variants with a
single stack except the Coldfire or '060 should do this.

-- 
 Chris Johns, cjohns @ cybertec.com.au