13.5.3 Power managementDisabling the MPU by clearing CESR[VLD] minimizes power dissipation. To minimizethe power dissipation of an enabled MPU, invalidate unused region descriptors byclearing the associated RGDn_Word3[VLD] bits.13.6 Initialization informationAt system startup, load the appropriate number of region descriptors, including settingRGDn_Word3[VLD]. Setting CESR[VLD] enables the module.If the system requires that all the loaded region descriptors be enabled simultaneously,first ensure that the entire MPU is disabled (CESR[VLD]=0).NoteIf the MPU registers are protected by the MPU, a regiondescriptor must be set to allow access to the MPU registers iffurther changes are needed.13.7 Application informationIn an operational system, interfacing with the MPU is generally classified into thefollowing activities:• Creating a new memory region—Load the appropriate region descriptor into anavailable RGDn, using four sequential 32-bit writes. The hardware assists in themaintenance of the valid bit, so if this approach is followed, there are no coherencyissues with the multi-cycle descriptor writes. (Clearing RGDn_Word3[VLD] deletes/removes an existing memory region.)• Altering only access privileges—To not affect the valid bit, write to the alternateversion of the access control word (RGDAACn), so there are no coherency issuesinvolved with the update. When the write completes, the memory region's accessrights switch instantaneously to the new value.• Changing a region's start and end addresses—Write a minimum of three words to theregion descriptor (RGDn_Word{0,1,3}). Word 0 and 1 redefine the start and endaddresses, respectively. Word 3 re-enables the region descriptor valid bit. In mostsituations, all four words of the region descriptor are rewritten.Initialization informationMWCT101xS Series Reference Manual, Rev. 3, 07/2019234 NXP Semiconductors
