MPU for ARMv7 (ARM R5)

Features Supported

APIs to setup MPU regions, including region address, size, attributes like access permissions, cache properties
APIs to enable, disable MPU
API to check if MPU is enabled

Features NOT Supported

NA

Important Usage Guidelines

Refer to ARMv7-R or ARMv7-M architecture manual for more details
The number of MPU entries varies based on the ARM R5, ARM M4 instantiated in a given DEVICE, refer DEVICE datasheet for more details.
In R5 for this DEVICE, there are 16 MPU regions

In M4 for this DEVICE, there are 16 MPU regions

MPU regions can overlap each other, with higher numbered regions taking more precedence in case of address overlaps.

Example Usage

Include the below file to access the APIs,

//! [include]
#include <kernel/dpl/CacheP.h>
#include <kernel/dpl/MpuP_armv7.h>
//! [include]

void samples()
{
//! [mpu]
    #define MAX_REGIONS (16u) /* Max regions on a R5F */

Example usage to setup MPU regions and enable MPU:

    MpuP_RegionAttrs regionParams;
    uint32_t regionId = 0;

    /* recommend to disable Cache and MPU before setting up MPU regions */
    CacheP_disable(CacheP_TYPE_ALL);
    MpuP_disable();

    /* make all 4G as strongly ordered, non-cacheable */
    MpuP_RegionAttrs_init(&regionParams);
    regionParams.isEnable = 1;
    regionParams.isCacheable = 0;
    regionParams.isBufferable = 0;
    regionParams.isSharable = 1;
    regionParams.isExecuteNever = 1; /* dont allow code execution */
    regionParams.tex = 0;
    regionParams.accessPerm = MpuP_AP_S_RW;
    MpuP_setRegion(regionId, (void*)0x00000000, MpuP_RegionSize_4G, &regionParams);
    regionId++;

    /* make ATCM as cacheable */
    MpuP_RegionAttrs_init(&regionParams);
    regionParams.isEnable = 1;
    regionParams.isCacheable = 1;
    regionParams.isBufferable = 1;
    regionParams.isSharable = 0;
    regionParams.isExecuteNever = 0; /* allow code execution */
    regionParams.tex = 1;
    regionParams.accessPerm = MpuP_AP_S_RW;
    MpuP_setRegion(regionId, (void*)0x00000000, MpuP_RegionSize_32K, &regionParams);
    regionId++;

    /* make memory region as strongly ordered, non-cacheable */
    MpuP_RegionAttrs_init(&regionParams);
    regionParams.isEnable = 1;
    regionParams.isCacheable = 0;
    regionParams.isBufferable = 0;
    regionParams.isSharable = 1;
    regionParams.isExecuteNever = 1; /* dont allow code execution */
    regionParams.tex = 0;

Example to setup MPU regions and enable MPU is shown below,

API Reference

Enums

enum MpuP_AccessPerm

Enum’s to represent different types of access permissions that are possible for a given MPU region.

Values:

enumerator MpuP_AP_ALL_BLOCK: All accesses are blocked

enumerator MpuP_AP_S_RW: Only RD+WR supervisor mode accesses are allowed

enumerator MpuP_AP_S_RW_U_R: RD+WR supervisor and RD only user mode accesses are allowed

enumerator MpuP_AP_ALL_RW: All RD+WR accesses are allowed

enumerator MpuP_AP_S_R: Only RD supervisor mode accesses are allowed

enumerator MpuP_AP_ALL_R: All RD accesses are allowed

enum MpuP_RegionSize

Enum’s to represent different possible MPU region size.

Values:

enumerator MpuP_RegionSize_32

enumerator MpuP_RegionSize_64

enumerator MpuP_RegionSize_128

enumerator MpuP_RegionSize_256

enumerator MpuP_RegionSize_512

enumerator MpuP_RegionSize_1K

enumerator MpuP_RegionSize_2K

enumerator MpuP_RegionSize_4K

enumerator MpuP_RegionSize_8K

enumerator MpuP_RegionSize_16K

enumerator MpuP_RegionSize_32K

enumerator MpuP_RegionSize_64K

enumerator MpuP_RegionSize_128K

enumerator MpuP_RegionSize_256K

enumerator MpuP_RegionSize_512K

enumerator MpuP_RegionSize_1M

enumerator MpuP_RegionSize_2M

enumerator MpuP_RegionSize_4M

enumerator MpuP_RegionSize_8M

enumerator MpuP_RegionSize_16M

enumerator MpuP_RegionSize_32M

enumerator MpuP_RegionSize_64M

enumerator MpuP_RegionSize_128M

enumerator MpuP_RegionSize_256M

enumerator MpuP_RegionSize_512M

enumerator MpuP_RegionSize_1G

enumerator MpuP_RegionSize_2G

enumerator MpuP_RegionSize_4G

Functions

void MpuP_RegionAttrs_init(MpuP_RegionAttrs *region)

Set default values to MpuP_RegionAttrs.

Strongly recommended to be called before seting values in MpuP_RegionAttrs

Parameters:: region – [out] parameter structure to set to default

void MpuP_setRegion(uint32_t regionNum, void *addr, uint32_t size, MpuP_RegionAttrs *attrs)

Setup a region in the MPU.

Note

Refer to ARMv7-R or ARMv7-M architecture manual for more details

Note

Recommended to disable MPU and disable cache before setting up MPU regions

Parameters:

regionNum – [in] region to setup
addr – [in] region start address, MUST aligned to region size
size – [in] region size, see MpuP_RegionSize
attrs – [in] region attrs, see MpuP_RegionAttrs

void MpuP_resetRegion(uint32_t regionNum)

Reset a region in the MPU.

Note

Refer to ARMv7-R or ARMv7-M architecture manual for more details

Parameters:: regionNum – [in] region to reset

void MpuP_enable(void): Enable MPU sub-system using the region that are setup using MpuP_setRegion.

void MpuP_disable(void): Disable MPU sub-system.

uint32_t MpuP_isEnable(void)

Check if MPU sub-system is enabled.

Returns:: 0: MPU sub-system is disabled, 1: MPU sub-system is enabled

void MpuP_init(void): Initialize MPU sub-system, called by SysConfig, not to be called by end users.

struct MpuP_RegionAttrs

#include <MpuP_armv7.h>

Attribute’s to apply for a MPU region.

Note

Refer to ARMv7-R or ARMv7-M architecture manual for more details

Note

C, B, S, TEX[0:2] bits together control if a region should be fully cached or non-cached or marked as device memory

Public Members

uint8_t isEnable: 1: enable this region, 0: disable this region

uint8_t isCacheable: 1: set C bit, 0: clear C bit

uint8_t isBufferable: 1: set B bit, 0: clear B bit

uint8_t isSharable: 1: set S bit, 0: clear S bit

uint8_t isExecuteNever: 1: set XN bit, 0: clear XN bit

uint8_t tex: set TEX[0:2] bits

uint8_t accessPerm: set AP[0:2] bits, see MpuP_AccessPerm

uint8_t subregionDisableMask: subregion disable mask, bitN = 1 means disable that subregion

struct MpuP_RegionConfig

#include <MpuP_armv7.h>

Region config structure, this used by SysConfig and not to be used by end-users directly.

Public Members

uint32_t baseAddr: region start address, MUST aligned to region size

uint32_t size: region size, see MpuP_RegionSize

MpuP_RegionAttrs attrs

struct MpuP_Config

#include <MpuP_armv7.h>

MPU config structure, this used by SysConfig and not to be used by end-users directly.

Public Members

uint32_t numRegions

uint32_t enableBackgroundRegion: Number of regions to configure 0: disable backgroun region, 1: enable background region

uint32_t enableMpu: 0: keep MPU disabled, 1: enable MPU