SAM L11 TrustZone Specific Register Access Protection

When the EVSYS is not PAC secured, non-secure and secure code can both access all functionalities. When the EVSYS is PAC secured, all registers are by default available in the secure alias only.

A PAC secured EVSYS can open up individual event channels and event users for non-secure access. This is done using the NONSECCHAN and NONSECUSER registers. When a channel or event user has been configured as non-secure, it can be handled from non-secure code using the EVSYS module non-secure alias. Since only Secured code has the rights to modify the NONSECCHAN and NONSECUSER registers, an interrupt-based mechanism has been added to let Non Secured code know when these registers have been changed by Secured code. A single flag called NSCHK in the INTFLAG register will rise should changes, conditioned by the NSCHKCHAN and NSCHKUSER registers, occur in the NONSECCHAN and NONSECUSER registers.

Note: Refer to the Mix-Secure Peripherals section in the SAM L11 Security Features chapter.