5.8.1. TCM attributes and permissions

Accesses to the TCMs from the LSU and PFU are checked against the MPU for access permission. Memory access attributes and permissions are not exported on this interface. Any unaligned access to Device or Strongly Ordered memory generates an alignment UsageFault. Reads that generate an MPU fault or alignment UsageFault are still sent to the TCM interface, but the data is not used and the associated load instruction does not update any processor registers, ensuring protection is maintained. Writes that generate an MPU fault or alignment UsageFault are never broadcast on the TCM interface.

TCMs always behave as Non-cacheable Non-shared Normal memory, irrespective of the memory type attributes defined in the MPU for a memory region containing addresses held in the TCM. Access permissions associated with an MPU region in the TCM address space are treated in the same way as addresses outside the TCM address space. For more information about memory attributes, types, and permissions, see the Arm®v7-M Architecture Reference Manual.

Note

For code portability to other Arm processors or systems, Arm recommends that TCM regions are always defined as Normal, Non-shared memory in the MPU. This is consistent with the default ARMv7E-M memory map attributes that apply when the MPU is either disabled or not implemented.

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