[FAQ] MCU-PLUS-SDK-AM263X: How to ensure the function access to certain critical variables are only restricted to certain functions ?

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#include <stdio.h>
#include <kernel/dpl/DebugP.h>
#include "ti_drivers_config.h"
#include "ti_drivers_open_close.h"
#include "ti_board_open_close.h"

MpuP_RegionConfig temp_function = {
    .baseAddr = 0x70080000,
    .size = MpuP_RegionSize_1K,
    .attrs.isEnable = 1,
    .attrs.isCacheable = 1,
    .attrs.isBufferable = 0,
    .attrs.isSharable = 1,
    .attrs.isExecuteNever = 1,
    .attrs.tex = 0,
    .attrs.accessPerm = 0,
    .attrs.subregionDisableMask = 0
};

uint8_t variable_function[1024] __attribute__((section(".data.test_function"))) = {0x01, 0x02, 0x03, 0x04, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F};

extern void MpuP_setRegionAsm(uint32_t regionId, uint32_t regionBaseAddr,
              uint32_t sizeAndEnble, uint32_t regionAttrs);

void MpuP_setRegionLocalFunction(uint32_t regionNum, void * addr, uint32_t size, MpuP_RegionAttrs *attrs)

{
    uint32_t baseAddress, sizeAndEnable;
    uintptr_t key;
    uint32_t value = size;

    DebugP_assertNoLog( regionNum < 16U);

    /* size 5b field */
    value = (value & (uint32_t)0x1F);

    /* If N is the value in size field, the region size is 2N+1 bytes. */
    sizeAndEnable = ((uint32_t)(attrs->subregionDisableMask & (uint32_t)0xFF) << (uint32_t)8)
                  | ((uint32_t)(value            & (uint32_t)0x1F) << (uint32_t)1)
                  | ((uint32_t)(attrs->isEnable &  (uint32_t)0x1) << (uint32_t)0);

    /* align base address to region size */
    baseAddress = ((uint32_t)addr & ~( (1U <<((uint64_t)value+1U))-1U ));

    /* get region attribute mask */
    uint32_t regionAttrs =
          ((uint32_t)(attrs->isExecuteNever & (uint32_t)0x1) << (uint32_t)12)
        | ((uint32_t)(attrs->accessPerm     & (uint32_t)0x7) << (uint32_t)8)
        | ((uint32_t)(attrs->tex            & (uint32_t)0x7) << (uint32_t)3)
        | ((uint32_t)(attrs->isSharable     & (uint32_t)0x1) << (uint32_t)2)
        | ((uint32_t)(attrs->isCacheable    & (uint32_t)0x1) << (uint32_t)1)
        | ((uint32_t)(attrs->isBufferable   & (uint32_t)0x1) << (uint32_t)0);

    key = HwiP_disable();

    MpuP_setRegionAsm(regionNum, baseAddress, sizeAndEnable, regionAttrs);

    HwiP_restore(key);
}

void function_a(void)
{
    /* Disable MPU */
    temp_function.attrs.isEnable = 0;
    MpuP_setRegionLocalFunction(4, (void *)temp_function.baseAddr, temp_function.size, (MpuP_RegionAttrs *)&temp_function.attrs.isEnable);
    /* Change the Access Permission */
    temp_function.attrs.accessPerm = 3;
    MpuP_setRegionLocalFunction(4, (void *)temp_function.baseAddr, temp_function.size, (MpuP_RegionAttrs *)&temp_function.attrs.isEnable);
    /* Enable MPU */
    temp_function.attrs.isEnable = 1;
    MpuP_setRegionLocalFunction(4, (void *)temp_function.baseAddr, temp_function.size, (MpuP_RegionAttrs *)&temp_function.attrs.isEnable);

    DebugP_log("Function A\r\n");
    /* Testing the Read Access */
    DebugP_log("Variable Function Data %x\r\n", variable_function[0]);
    /* Testing the Write Access */
    variable_function[0] = 0xFF;
    /* Testing the Read Access again to prevent optimization */
    DebugP_log("Variable Function Data %x\r\n", variable_function[0]);

    /* Disable MPU */
    temp_function.attrs.isEnable = 0;
    MpuP_setRegionLocalFunction(4, (void *)temp_function.baseAddr, temp_function.size, (MpuP_RegionAttrs *)&temp_function.attrs.isEnable);

    /* Revert the Access Permission */
    temp_function.attrs.accessPerm = 0;
    MpuP_setRegionLocalFunction(4, (void *)temp_function.baseAddr, temp_function.size, (MpuP_RegionAttrs *)&temp_function.attrs.isEnable);

    /* Enable MPU */
    temp_function.attrs.isEnable = 1;
    MpuP_setRegionLocalFunction(4, (void *)temp_function.baseAddr, temp_function.size, (MpuP_RegionAttrs *)&temp_function.attrs.isEnable);
}

void function_b(void)
{
    /* Disable MPU */
    temp_function.attrs.isEnable = 0;
    MpuP_setRegionLocalFunction(4, (void *)temp_function.baseAddr, temp_function.size, (MpuP_RegionAttrs *)&temp_function.attrs.isEnable);

    /* Revert the Access Permission */
    temp_function.attrs.accessPerm = 6;
    MpuP_setRegionLocalFunction(4, (void *)temp_function.baseAddr, temp_function.size, (MpuP_RegionAttrs *)&temp_function.attrs.isEnable);

    /* Enable MPU */
    temp_function.attrs.isEnable = 1;
    MpuP_setRegionLocalFunction(4, (void *)temp_function.baseAddr, temp_function.size, (MpuP_RegionAttrs *)&temp_function.attrs.isEnable);

    DebugP_log("Function B\r\n");
    DebugP_log("Variable Function Data %x\r\n", variable_function[0]);
    /* Writing will lead to abort, so commented */
    //variable_function[0] = 0xAA;

    /* Disable MPU */
    temp_function.attrs.isEnable = 0;
    MpuP_setRegionLocalFunction(4, (void *)temp_function.baseAddr, temp_function.size, (MpuP_RegionAttrs *)&temp_function.attrs.isEnable);

    /* Revert the Access Permission */
    temp_function.attrs.accessPerm = 0;
    MpuP_setRegionLocalFunction(4, (void *)temp_function.baseAddr, temp_function.size, (MpuP_RegionAttrs *)&temp_function.attrs.isEnable);

    /* Enable MPU */
    temp_function.attrs.isEnable = 1;
    MpuP_setRegionLocalFunction(4, (void *)temp_function.baseAddr, temp_function.size, (MpuP_RegionAttrs *)&temp_function.attrs.isEnable);
}

void function_c(void)
{
    DebugP_log("Function C\r\n");
    /* Reading will lead to abort, so commented */
    //DebugP_log("Variable Function Data %x\r\n", variable_function[0]);
    /* Writing will lead to abort, so commented */
    //variable_function[0] = 0xCC;
}

void hello_world_main(void *args)
{
    /* Open drivers to open the UART driver for console */
    Drivers_open();
    Board_driversOpen();
    //DebugP_log("Hello World!\r\n");

    /* A Function which can read and write the variable */
    function_a();

    /* A Function which can read the variable */
    function_b();

    /* A Function which cannot access the variable */
    function_c();

    Board_driversClose();
    Drivers_close();
}