SWRU626 December 2025 CC3501E , CC3551E
It is a hardware inside the processor which allow Secure software to define Non-secure and Non-Secure Callable (NSC) regions. Regions that are not mapped to any SAU regions are Secure by default. The results from SAU and Implementation Defined Attribution Unit (IDAU) are compared, and higher security attribute is selected. For example, if SAU indicates a memory location is Secure and IDAU indicate the same address as Non-secure, the processor treats it as Secure. The order of security levels from low to high is Non-secure < N-Secure Callable < Secure.