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Nexus does not bypass MPU on MPC5644A?

Question asked by Etienne Alepins on Feb 9, 2016
Latest reply on Feb 11, 2016 by Lukas Zadrapa



We are using the MPC5644A. We configure the MPU dynamically (the config changes very often) to allow the core to access only parts of the RAM. Indeed, there are multiple processes running on the core which have different privileges. We are having a debugging issue where we cannot look at variables from another process when we have set a breakpoint in a first process. This is because the MPU forbits that process to read variables of the other process. However, we would have expected the debugger to bypass access permissions!


There is no specific enable fields for the Nexus/JTAG in the MPU_RGDn.Word2 register. Indeed, the XBAR chapter in the RM seems to say that the core data port (M1) is used by the Nexus to access memory and so that the MPU cannot see the difference between the core and the debug module. Is that true? If so, isn't that a bad design? Is this solved in newer MCUs like MPC57xx?