mpc555 memory mapping

I'm wondering if someone can help me with a memory mapping question.

We've got a custom 555 board with 4MB of external RAM, all on one CS.
When running from internal flash, the base address of the 555 is
0x000000 and the external RAM is mapped to address 0x400000. When
we're debugging, we disable the internal flash and map the external
RAM to address 0x000000. In this debug configuration, we can't access
external RAM addresses from 0x2FC000 to 0x3FFFFF because those are
assigned to internal 555 registers and internal RAM.

My question is whether there is a way to map the memory for debug so
that the code runs from external RAM, but the address ranges of the
555 and the external RAM don't overlap? We've actually done this, and
it works until the first interrupt occurs. As far as I can tell, the
exception vectors can ONLY be located at the base address of the 555
or to that address + 32K. If that table is in RAM, along with the
other code, then there doesn't seem to be any way to avoid mapping the
external RAM to the same address as the base address of the 555.

Is using ETRE part of the problem? If so, we could stop using that
feature.

Any help will be greatly appreciated.

Joe





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