MPU for ARMv7 (ARM R5, ARM M4)

Table of Contents

• Features Supported
• Features NOT Supported
• Important Usage Guidelines
• Example Usage
• API

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-M architecture manual for more details
• The number of MPU entries varies based on the ARM M4 instantiated in a given DEVICE, refer DEVICE datasheet for more details.
• 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 <kernel/dpl/CacheP.h>
#include <kernel/dpl/MpuP_armv7.h>

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

    #define MAX_REGIONS (16u) /* Max regions on a R5F */
 
    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;
    regionParams.accessPerm = MpuP_AP_S_RW;
    MpuP_setRegion(regionId, (void*)0x02000000, MpuP_RegionSize_32K, &regionParams);
    regionId++;
 
    if(regionId >= MAX_REGIONS)
    {
        while(1) { ; }
        /* Typically MPU setup happens very early in the boot sequence,
         * at this point DebugP_assert(), DebugP_log() are not available
         */
    }
 
    /* enable Cache and MPU after setting up MPU regions */
    MpuP_enable();
    CacheP_enable(CacheP_TYPE_ALL);
 
 

API

APIs for MPU for ARMv7 (ARM R5, ARM M4)