UCOSIII优先级反转

梦里梦外; 2022-06-02 00:05 168阅读 0赞

**反转现象**  
![1][]  
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**  
![1][1 1]

**解决办法**  
`UCOSIII互斥信号量：`[http://blog.csdn.net/zhangxuechao\_/article/details/78912647][http_blog.csdn.net_zhangxuechao_article_details_78912647]

[1]: /images/20220602/4874f00046aa48fab70177d681c99fd2.png
[1 1]: /images/20220602/1b1853033a20489f900097e925eae875.png
[http_blog.csdn.net_zhangxuechao_article_details_78912647]: http://blog.csdn.net/zhangxuechao_/article/details/78912647