ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Address range
Behavior of an implementation that does not include an MPU
Protected Memory System Architecture (PMSA)
If a PMSAv7 implementation does not include an MPU, it must adopt the default memory map behavior
described in Behavior when the MPU is disabled on page B4-5.
A PMSAv7 implementation that does not include an MPU is identified by an MPU Type Register entry that
shows a Unified MPU with zero Data or Unified regions, see c0, MPU Type Register (MPUIR) on
page B4-36.
B4.1.6 Finding the minimum supported region size
Table B4-2 Default memory map, showing data access attributes
Data memory type
Caching enabled a Caching disabled
0xFFFFFFFF - 0xC0000000 Strongly-ordered Strongly-ordered
0xBFFFFFFF - 0xA0000000 Shareable Device Shareable Device
0x9FFFFFFF - 0x80000000 Non-shareable Device Non-shareable Device
0x7FFFFFFF - 0x60000000 Normal, Shareable, Non-cacheable Normal, Shareable, Non-cacheable
0x5FFFFFFF - 0x40000000 Normal, Non-shareable, Write-Through
Cacheable
0x3FFFFFFF - 0x00000000 Normal, Non-shareable, Write-Back,
Write-Allocate Cacheable
Normal, Shareable, Non-cacheable
Normal, Shareable, Non-cacheable
a. Caching is enabled for data accesses if the data or unified caches are enabled. See the description of the C bit in
c1, System Control Register (SCTLR) on page B4-45.
You can use the DRBAR to find the minimum region size supported by an implementation, by following
this procedure:
1. Write a valid memory region number to the RGNR. Normally you use region number 0, because this
is always a valid region number.
2. Write the value 0xFFFFFFFC to the DRBAR. This value sets all valid bits in the register to 1.
3. Read back the value of the DRBAR. In the returned value the least significant bit set indicates the
resolution of the selected region. If the least significant bit set is bit M the resolution of the region is
2 M bytes.
If the MPU implements separate data and instruction regions this process gives the minimum size for data
regions. To find the minimum size for instruction regions, use the same procedure with the IRBAR.
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. B4-7