0x4000

0x0800

0x0000

Memory Protection Unit

Stack

Guard region

Figure 7-3 Overlapping subregion of memory

7.1.3Background regions

Overlapping regions increase the flexibility of how the regions can be mapped onto physical memory devices in the system. You can also use the overlapping properties to specify a background region. For example, you might have a number of physical memory areas sparsely distributed across the 4GB address space. If a programming error occurs, the processor might issue an address that does not fall into any defined region.

If the address that the processor issues falls outside any of the defined regions, the MPU is hard-wired to abort the access. That is, all accesses for an address that is not mapped to a region in the MPU generate a background fault. You can override this behavior by programming region 0 as a 4GB background region. In this way, if the address does not fall into any of the other 11 regions, the attributes and access permissions you specified for region 0 control the access.

In Privileged modes, you can also override this behavior by setting the BR bit, bit [17], of the System Control Register. This causes Privileged accesses that fall outside any of the defined regions to use the default memory map.

7.1.4TCM regions

Any memory address that you configure to be accessed using a TCM interface is given Normal, Non-shared type attributes, regardless of the attributes of any MPU region that the address also belongs to. Access permissions for an address in a TCM region are preserved from the MPU region that the address also belongs to. For more information, see About the TCMs on page 8-13.

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ARM R4F, r1p3 manual Background regions, TCM regions