Implementation Defined Attribution Unit (IDAU)
The ARM®v8‑M architecture defines a mechanism whereby an implementation can define whether any particular address is exempt from checking, is NSC or Secure. If the ARMv8‑M Security Extension is included, then the internal Secure Attribution Unit (SAU) or an external Implementation Defined Attribution Unit (IDAU) determines the Security state attributed to each address.
The number of SAU regions is defined during the implementation of the processor. If no SAU regions are defined, or the SAU is disabled, and no IDAU is included in the system then the entire memory address space is Secure and the processor is not able to switch to Non-secure state.
This section contains the following subsections: