Difference between Sub regions and Overlapping Regions in MPU

Overlapping regions:

Each region is defined by a base address, a size and some attributes.

If you define multiple regions, it is possible some might overlap.  For example:

Region A: Covers 1MB starting at 0x0

Region B: Covers 4KB starting 0x10000

The address range 0x10000-0x10FFF is now covered by both A and B.  So which attributes should it use?  The overlapping region rules in the PMSA describes how this is resolved.

Sub-regions:

Each region (as long as it's at least 256 bytes) is sub-divided into 8 sub-regions.  With an enable bit per sub-region.  Effectively allowing you to "poke a hole" in a region.  The corresponding addresses are not treated as part of the region.  They will either pick-up the attributes of an overlapping region (if there is one), or use the defaults.

Allowing overlapping and sub-regions gives you flexibility, and can in many cases reduce the total number of regions you need to define.

Overlapping regions:

Each region is defined by a base address, a size and some attributes.

If you define multiple regions, it is possible some might overlap.  For example:

Region A: Covers 1MB starting at 0x0

Region B: Covers 4KB starting 0x10000

The address range 0x10000-0x10FFF is now covered by both A and B.  So which attributes should it use?  The overlapping region rules in the PMSA describes how this is resolved.

Sub-regions:

Each region (as long as it's at least 256 bytes) is sub-divided into 8 sub-regions.  With an enable bit per sub-region.  Effectively allowing you to "poke a hole" in a region.  The corresponding addresses are not treated as part of the region.  They will either pick-up the attributes of an overlapping region (if there is one), or use the defaults.

Allowing overlapping and sub-regions gives you flexibility, and can in many cases reduce the total number of regions you need to define.

Thanks for the reply martin.

Regards,

Techguyz