## Security Attribution Unit

The Arm Cortex-M33 processor implementation in RSL15 is supported by a programmable security attribution unit (SAU), which is used for controlling accesses to items mapped into the Arm Cortex-M33 processor's memory-map. The SAU supports the definition of between 0 and 4 regions of memory that can be made accessible for use with TrustZone non-secure applications.

For instructions and data, the SAU returns the security attribute that is associated with the address.

- For instructions, the attribute determines the allowable security state of the processor when the instruction is executed. It can also identify whether code at a secure address can be called from a non-secure state.
- For data, the attribute determines whether a memory address can be accessed from the non-secure execution state, and whether the external memory request is marked as secure or non-secure.
- If a data access is made from the non-secure execution state to an address marked as secure, then a SecureFault exception is taken by the processor. If a data access is made from the secure execution state to an address marked as non-secure, then the associated memory access is marked as non-secure.

For information on using the security attribution unit as part of a secure/non-secure application pair, see TrustZone. For more general information on the SAU, refer to the Arm v8-M Architecture Reference Manual and the Arm Cortex-M33 Processor Technical Reference Manual.

IMPORTANT: For best practices in error, fault, and watchdog interrupt handling see Diagnostic Strategies from the RSL15 Developer's Guide.

For this peripheral’s registers, see Security Attribution Unit Registers.