SWCU194 March 2023 CC1314R10 , CC1354P10 , CC1354R10 , CC2674P10 , CC2674R10
The intended use is to implement a Secure-side execution environment that manages security sensitive system tasks and cryptography. System tasks include writing to Flash (can affect the security execution environment), managing power (can effect execution flow and hence indirectly affect Secure code) as well as some other system settings that might affect the security execution environment.
The watermark registers can be configured either by the pre-allocated CCFG settings or by the initialization of the program that runs in Secure execution environment. The watermark registers statically configure the IDAU to determine Secure regions and Non-secure regions in Flash and SRAM memory. These Secure memory regions (Flash and SRAM) along with Secure periphery, isolated from code running as Non-secure, can then be used for cryptographic operations and key management.
A lock mechanism is provided so that the settings can be locked into place until the next reset.
The user can use the Secure Attribution Unit (SAU) to further configure other memory attributes to extend the functionality.
However, SAU attributes are only enforced for the Cortex-M33. The SAU attributes are not enforced for other bus initiators in the system, including the μDMA, I2S, and AES and Hash Cryptoprocessor. Therefore, use of the SAU is not recommended.