4.3.1. Background regions

Overlapping regions increase the flexibility of how the eight 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 therefore, it might be possible for the processor to issue an address that does not fall into any defined region.

If the address issued by the processor falls outside any of the defined regions, the ARM946E-S protection unit is hard-wired to abort the access. You can override this behavior by programming region 0 to be a 4GB background region. In this way, if the address does not fall into any of the other seven regions, the access is controlled by the attributes you have specified for region 0.

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