System resources separation

When TrustZone-M is enabled, all areas mapped in memory, including RAM, peripherals, and even FLASH storage, receive a new security attribute. Besides the secure and non-secure domains, a security attribute may assume a third value, Non-Secure Callable (NSC). This last attribute defines special regions of memory used to implement transactions from the non-secure world to the secure world through a specific mechanism, which will be explained in the last section, Building and running the example. An NSC area is used to offer secure APIs that act like system calls with new powers. The secure domain exposes service routines that can perform specific controlled actions while accessing secure resources from its non-secure counterpart.

Security attributes and memory regions

Cortex-M33 microcontrollers offer various levels of protection. The combination of the effects of those levels determines which of the memory-mapped areas associated with a resource on...