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