2.2.4. Subregion disable

With the exception of region 0, you can program the TZASC to disable any or all of the eight subregions that comprise a region. When a subregion is disabled, the security permissions for its address range are provided by the next highest priority region that overlaps the address range.

Example 2.1. Example configuration for subregion disable

Figure 2.5 shows an example configuration that supports four regions, where:

  • region 2 and region 3 are partially overlapped

  • region 1 and region 3 are partially overlapped

  • region 0 is overlapped with all regions.

With some subregions of region 1, region 2, and region 3 are disabled, and the resulting region permissions of the entire address space is shown in the Figure 2.5.


Figure 2.5. Subregion disable example


Note

In Figure 2.5:

  • all subregions are enabled unless otherwise stated

  • spn represents the region permissions of region n.

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