SWRU626 December 2025 CC3501E , CC3551E
The IDAU does not attribute any region directly as secure (S) because it is not allowed to change a S region to NSC. For addresses attributed Execute-never (XN) the distinction does not matter but for executable memory the user is responsible to use the SAU to mark regions not intended to be NSC as S. Best practice is to mark all Flash and SRAM that does not explicitly hold the SG (Secure Gateway) instructions as S or NS. I.e. mark all but a region of the Flash and SRAM NSC regions as S where the remaining region holds all the SG instructions. If you do not execute secure code with SG calls from NS in SRAM mark all of SRAM NSC region as S.