SEVERE Bug in mc68360 _ISR_Handler???

Chris Johns cjohns at
Tue Jul 17 13:48:59 UTC 2001

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
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

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 @

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