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armv8-m mpu: how to mark one region with no any access?

sword_i@sina.com

For the ARMv8M mpu, there is only two bits for the AP(access permission), another

XN bit for executable. 

I wan't to mark a region (e.g. from 0~4096) with no any access, mainly used for NULL pointer

read/write check. For ARMv7M, the mpu has 3 bits  in AP field(RASR register), and I can select 000

to mark this region no any access, but for ARMv8M, there is only two bits in the register

MPU_RBAR,

"

00 – read/write by privileged code only
01 – read/write by any privilege level
10 – Read only by privileged code only
11 – Read only by any privilege level

"

So, how should I do with the new MPU? any advice will be appreciated.

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  • +1

    Hi,

    In Armv8-M, MPU can be programmed only to the regions that need to be accessed by either data access operations or instruction execution.

    If a memory spaced is not programmed by a MPU region, then on either a data or instruction access fault is triggered.

    Hence, there is no need of using one more MPU region to mark a memory space with "No Access" by both data and instruction access operations.

    Thanks,

    Uma

Reply
  • +1

    Hi,

    In Armv8-M, MPU can be programmed only to the regions that need to be accessed by either data access operations or instruction execution.

    If a memory spaced is not programmed by a MPU region, then on either a data or instruction access fault is triggered.

    Hence, there is no need of using one more MPU region to mark a memory space with "No Access" by both data and instruction access operations.

    Thanks,

    Uma

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