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MPC8xx BDM modules and gdb

 > I have been asked about this and did not have a quick answer.  Could
 > someone enlighten me?

By my best knowledge there's no such beast yet, at least not an open
source one.

The 68k BDM works by issuing BDM specific commands to read/write 
registers, memory, start and stop the CPU, etc.

The MPC BDM is a rather different animal. It differs in its HW, but
more importantly, you don't issue BDM specific commands but you can
make the CPU to execute an instruction provided through the BDM. That
is, when you read a CPU register you download an PPC insn that is a 
move from rx to the BDM_data special register, the PPC will execute
this insn then you can then read the BDM data register through the 
interface. All operations work like that.

I was going to write a driver under Linux but our customer decided to
use 683xx instead of the MPC850 for cost reasons so this project of 
mine has been abandoned :-(.