UCOSIII优先级反转

反转现象



任务优先级：H>M>L

绿色部分：任务占用共享资源

理想状态：7释放信号量后，最高优先级H任务抢占CPU

反转原因：H和L等待同一个信号量，H的任务优先级被降至和L相同优先级，此时M已经成为最高优先级

实验举例

void start_task(void *p_arg)

{

    OS_CRITICAL_ENTER();    //进入临界区

    //创建一个信号量

    OSSemCreate ((OS_SEM*   )&TEST_SEM,

                 (CPU_CHAR* )"TEST_SEM",

                 (OS_SEM_CTR)1,             //信号量初始值为1

                 (OS_ERR*   )&err);

    //创建HIGH任务

    OSTaskCreate((OS_TCB    * )&High_TaskTCB,

                 (CPU_CHAR  * )"High task",

                 (OS_TASK_PTR )high_task,

                 (void      * )0,

                 (OS_PRIO     )HIGH_TASK_PRIO,

                 (CPU_STK   * )&HIGH_TASK_STK[0],

                 (CPU_STK_SIZE)HIGH_STK_SIZE/10,

                 (CPU_STK_SIZE)HIGH_STK_SIZE,

                 (OS_MSG_QTY  )0,

                 (OS_TICK     )0,

                 (void      * )0,

                 (OS_OPT      )OS_OPT_TASK_STK_CHK|OS_OPT_TASK_STK_CLR,

                 (OS_ERR    * )&err);

    //创建MIDDLE任务

    OSTaskCreate((OS_TCB    * )&Middle_TaskTCB,

                 (CPU_CHAR  * )"Middle task",

                 (OS_TASK_PTR )middle_task,

                 (void      * )0,

                 (OS_PRIO     )MIDDLE_TASK_PRIO,

                 (CPU_STK   * )&MIDDLE_TASK_STK[0],

                 (CPU_STK_SIZE)MIDDLE_STK_SIZE/10,

                 (CPU_STK_SIZE)MIDDLE_STK_SIZE,

                 (OS_MSG_QTY  )0,

                 (OS_TICK     )0,

                 (void      * )0,

                 (OS_OPT      )OS_OPT_TASK_STK_CHK|OS_OPT_TASK_STK_CLR,

                 (OS_ERR    * )&err);

    //创建LOW任务

    OSTaskCreate((OS_TCB    * )&Low_TaskTCB,

                 (CPU_CHAR  * )"Low task",

                 (OS_TASK_PTR )low_task,

                 (void      * )0,

                 (OS_PRIO     )LOW_TASK_PRIO,

                 (CPU_STK   * )&LOW_TASK_STK[0],

                 (CPU_STK_SIZE)LOW_STK_SIZE/10,

                 (CPU_STK_SIZE)LOW_STK_SIZE,

                 (OS_MSG_QTY  )0,

                 (OS_TICK     )0,

                 (void      * )0,

                 (OS_OPT      )OS_OPT_TASK_STK_CHK|OS_OPT_TASK_STK_CLR,

                 (OS_ERR    * )&err);

    OS_CRITICAL_EXIT(); //退出临界区

}

//高优先级任务的任务函数

void high_task(void *p_arg)

{

    OS_ERR err;

    CPU_SR_ALLOC();

    while(1)

    {

        OSTimeDlyHMSM(0,0,0,500,OS_OPT_TIME_PERIODIC,&err);     //延时500ms

        printf("high task Pend Sem\r\n");

        OSSemPend(&TEST_SEM,0,OS_OPT_PEND_BLOCKING,0,&err);     //请求信号量

        printf("high task Running!\r\n");

        OSSemPost(&TEST_SEM,OS_OPT_POST_1,&err);                //释放信号量

        OSTimeDlyHMSM(0,0,0,500,OS_OPT_TIME_PERIODIC,&err);     //延时500ms

    }

}

//中等优先级任务的任务函数

void middle_task(void *p_arg)

{

    OS_ERR err;

    CPU_SR_ALLOC();

    while(1)

    {

        printf("middle task Running!\r\n");

        OSTimeDlyHMSM(0,0,1,0,OS_OPT_TIME_PERIODIC,&err);   //延时1s

    }

}

//低优先级任务的任务函数

void low_task(void *p_arg)

{

    static u32 times;

    OS_ERR err;

    while(1)

    {

        OSSemPend(&TEST_SEM,0,OS_OPT_PEND_BLOCKING,0,&err); //请求信号量

        printf("low task Running!\r\n");

        for(times=0;times<5000000;times++)

        {

            OSSched();                                      //发起任务调度

        }

        OSSemPost(&TEST_SEM,OS_OPT_POST_1,&err);

        OSTimeDlyHMSM(0,0,1,0,OS_OPT_TIME_PERIODIC,&err);   //延时1s

    }

}

实验现象

解决办法

UCOSIII互斥信号量：http://blog.csdn.net/zhangxuechao_/article/details/78912647