ARM946E-S™ Technical Reference Manual 2.3.9. Register 6, Protection Region Base and Size Registers

2.3.9. Register 6, Protection Region Base and Size Registers

These registers define the protection region base address and size. You can define eight programmable regions using these registers. The values are ignored when the protection unit is disabled, and on reset only the region enable bit for each region is reset to 0. All other bits are undefined. You must program at least one memory region before you enable the protection unit.

The instructions used to access the eight Protection Region Base and Size Registers are listed in Table 2.16.

Table 2.16. Accessing Protection Region Base and Size Registers

ARM instruction	Protection Region Base and Size Register
`MCR/MRC p15, 0, Rd, c6, c7, 0`	Memory region 7
`MCR/MRC p15, 0, Rd, c6, c6, 0`	Memory region 6
`MCR/MRC p15, 0, Rd, c6, c5, 0`	Memory region 5
`MCR/MRC p15, 0, Rd, c6, c4, 0`	Memory region 4
`MCR/MRC p15, 0, Rd, c6, c3, 0`	Memory region 3
`MCR/MRC p15, 0, Rd, c6, c2, 0`	Memory region 2
`MCR/MRC p15, 0, Rd, c6, c1, 0`	Memory region 1
`MCR/MRC p15, 0, Rd, c6, c0, 0`	Memory region 0

Each Protection Region Base and Size Register has the format shown in Table 2.17.

Table 2.17. Protection Region Base and Size Register format

Register bits	Function
[31:12]	Region base address
[5:1]	Region size
[0]	1 = Region enable 0 = Region disable Reset to 0

Function

[31:12]

Region base address

[5:1]

Region size

[0]

1 = Region enable

0 = Region disable

Reset to 0

You must align the region base to a region size boundary, where the region size is defined in its respective protection region register. The behavior is Unpredictable if this is not done.

Region sizes are encoded as shown in Table 2.18.

Table 2.18. Region size encoding

Bit encoding	Region size
b00000 to b01010	Reserved (UNP)
b01011	4KB
b01100	8KB
b01101	16KB
b01110	32KB
b01111	64KB
b10000	128KB
b10001	256KB
b10010	512KB
b10011	1MB
b10100	2MB
b10101	4MB
b10110	8MB
b10111	16MB
b11000	32MB
b11001	64MB
b11010	128MB
b11011	256MB
b11100	512MB
b11101	1GB
b11110	2GB
b11111	4GB

Example base setting

An 8KB size region aligned to an 8KB boundary at 0x00002000 (covering the address range 0x00002000-0x00003FFF) is programmed as 0x00002019.

The following instruction is supported for backward compatibility with other ARM processors using a memory protection unit:

MRC p15, 0, Rd, c6, CRm, 1; returns protection region register

This instruction enables the protection region registers to be read.

You must not write to the protection region base and size registers with opcode_2 set to 1 because the behavior is Unpredictable.

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