[参考译文] AM2634：ARM MPU 示例、如何设置

尊敬的 Aakash：

非常感谢您的立即回应,并很抱歉我的延迟回复。 从您的示例代码中、我了解如何设置和使用 MPU。 我只有一个问题：  

请告诉我、我的理解是否正确？

每次必须执行以下操作时访问受保护区域：

1. 禁用 MPU

2. 更改访问权限(以获取访问权限)

3. 启用 MPU  

访问之后、我应该再次：

1. 禁用 MPU

2. 更改访问权限(恢复访问权限)

3. 启用 MPU  

这是我通常应该如何使用 MPU 吗？另外、是否有必要执行第二部分、即恢复访问？ 如果我不撤消访问、会发生什么情况？

非常感谢您的帮助。

此致、

哈沙

尊敬的 Aakash：

我尝试了以上示例、但似乎失败了。 请让我知道我在这里犯了什么错。

/*
 *  Copyright (C) 2021 Texas Instruments Incorporated
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 *    notice, this list of conditions and the following disclaimer.
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 *    distribution.
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 *    its contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 *  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 *  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 *  A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 *  OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 *  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 *  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 *  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <stdio.h>
#include <kernel/dpl/DebugP.h>
#include <kernel/dpl/MpuP_armv7.h>
#include "ti_drivers_config.h"
#include "ti_drivers_open_close.h"
#include "ti_board_open_close.h"


/*
 * This is an empty project provided for all cores present in the device.
 * User can use this project to start their application by adding more SysConfig modules.
 *
 * This application does driver and board init and just prints the pass string on the console.
 * In case of the main core, the print is redirected to the UART console.
 * For all other cores, CCS prints are used.
 */
MpuP_RegionConfig localMpuRegionConfig = {
                                      .baseAddr = 0x70080000,
                                      .size = MpuP_RegionSize_1K,
                                      .attrs = {
                                          .isEnable = 1,
                                          .isCacheable = 1,
                                          .isBufferable = 0,
                                          .isSharable = 1,
                                          .isExecuteNever = 1,
                                          .tex = 0,
                                          .accessPerm = MpuP_AP_ALL_BLOCK,
                                          .subregionDisableMask = 0x0u
                                      },
                                    };

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

void access_permission_set(uint16_t perm)
{
    /* Disable MPU */
    localMpuRegionConfig.attrs.isEnable = 0;
    localMpuRegionConfig.attrs.isCacheable = 0;
    MpuP_setRegion(6, (void *)localMpuRegionConfig.baseAddr, localMpuRegionConfig.size, (MpuP_RegionAttrs *)&localMpuRegionConfig.attrs);
    /* Change the Access Permission */
    localMpuRegionConfig.attrs.accessPerm = (uint8_t)perm;
    MpuP_setRegion(6, (void *)localMpuRegionConfig.baseAddr, localMpuRegionConfig.size, (MpuP_RegionAttrs *)&localMpuRegionConfig.attrs);
    /* Enable MPU */
    localMpuRegionConfig.attrs.isEnable = 1;
    localMpuRegionConfig.attrs.isCacheable = 1;
    MpuP_setRegion(6, (void *)localMpuRegionConfig.baseAddr, localMpuRegionConfig.size, (MpuP_RegionAttrs *)&localMpuRegionConfig.attrs);
}

void function_a(void)
{
    access_permission_set(MpuP_AP_ALL_RW);

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

    access_permission_set(MpuP_AP_ALL_BLOCK);
}

void function_b(void)
{
    access_permission_set(MpuP_AP_ALL_R);

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

    access_permission_set(MpuP_AP_ALL_BLOCK);
}

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


void empty_main(void *args)
{
    /* Open drivers to open the UART driver for console */
    Drivers_open();
    Board_driversOpen();

    function_a();
    function_b();
    function_c();

    DebugP_log("All tests have passed!!\r\n");

    while(1)
    {

    }

    Board_driversClose();
    Drivers_close();
}

syscfg 中的 MPU 配置

UART 端子上的输出：

函数 b 和 c 应该已经触发中止、但它们都不应该触发。

电源发展   

此致、

哈沙