FreeRTOS任務優先級數值越小優先級越低，系統在運行過程中允許修改任務優先級

修改任務優先級的主要工作包括：

如果新的優先級大于當前任務優先級，則請求切換

重新設置事件列表值

將任務從原就緒列表中移除并掛接到新的就緒列表中

/* 設置任務優先級 */ void vTaskPrioritySet(TaskHandle_t xTask, UBaseType_t uxNewPriority) {TCB_t *pxTCB;UBaseType_t uxCurrentBasePriority, uxPriorityUsedOnEntry;BaseType_t xYieldRequired = pdFALSE;configASSERT((uxNewPriority < configMAX_PRIORITIES));/* 任務優先級不能超過最大值 */if(uxNewPriority >= (UBaseType_t)configMAX_PRIORITIES){uxNewPriority = (UBaseType_t)configMAX_PRIORITIES - (UBaseType_t)1U;}else{mtCOVERAGE_TEST_MARKER();}taskENTER_CRITICAL();{/* 通過任務句柄獲取任務TCB */pxTCB = prvGetTCBFromHandle(xTask);traceTASK_PRIORITY_SET(pxTCB, uxNewPriority);#if (configUSE_MUTEXES == 1){uxCurrentBasePriority = pxTCB->uxBasePriority;}#else{/* 記錄原先的優先級 */uxCurrentBasePriority = pxTCB->uxPriority;}#endif/* 優先級和原先優先級不同 */if(uxCurrentBasePriority != uxNewPriority){/* 新優先級大于原優先級 */if(uxNewPriority > uxCurrentBasePriority){/* 該任務不是當前任務 */if(pxTCB != pxCurrentTCB){/* 新優先級大于當前任務優先級 */if(uxNewPriority >= pxCurrentTCB->uxPriority){/* 請求切換任務 */xYieldRequired = pdTRUE;}else{mtCOVERAGE_TEST_MARKER();}}else{}}/* 該任務為當前任務 */else if(pxTCB == pxCurrentTCB){/* 請求切換任務 */xYieldRequired = pdTRUE;}else{}/* 記錄原優先級 */uxPriorityUsedOnEntry = pxTCB->uxPriority;#if (configUSE_MUTEXES == 1){if(pxTCB->uxBasePriority == pxTCB->uxPriority){pxTCB->uxPriority = uxNewPriority;}else{mtCOVERAGE_TEST_MARKER();}pxTCB->uxBasePriority = uxNewPriority;}#else{/* 設置新優先級 */pxTCB->uxPriority = uxNewPriority;}#endif/* 重新設置事件列表項的值 */if((listGET_LIST_ITEM_VALUE(&(pxTCB->xEventListItem)) & taskEVENT_LIST_ITEM_VALUE_IN_USE) == 0UL){listSET_LIST_ITEM_VALUE(&(pxTCB->xEventListItem), ((TickType_t)configMAX_PRIORITIES - (TickType_t)uxNewPriority));}else{mtCOVERAGE_TEST_MARKER();}/* 任務在就緒列表中 */if(listIS_CONTAINED_WITHIN(&(pxReadyTasksLists[uxPriorityUsedOnEntry]), &(pxTCB->xStateListItem)) != pdFALSE){/* 從原就緒列表中移除，就緒列表已經沒有任務 */if(uxListRemove(&(pxTCB->xStateListItem)) == (UBaseType_t)0){/* 清除任務優先級記錄中的優先級 */portRESET_READY_PRIORITY(uxPriorityUsedOnEntry, uxTopReadyPriority);}else{mtCOVERAGE_TEST_MARKER();}/* 將任務加入新的就緒列表 */prvAddTaskToReadyList(pxTCB);}else{mtCOVERAGE_TEST_MARKER();}/* 需要請求切換任務 */if(xYieldRequired != pdFALSE){taskYIELD_IF_USING_PREEMPTION();}else{mtCOVERAGE_TEST_MARKER();}(void)uxPriorityUsedOnEntry;}}taskEXIT_CRITICAL(); }

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系統也提供了獲取任務優先級的接口，程序比較簡單

/* 獲取任務優先級 */ UBaseType_t uxTaskPriorityGet(const TaskHandle_t xTask) {TCB_t const *pxTCB;UBaseType_t uxReturn;taskENTER_CRITICAL();{pxTCB = prvGetTCBFromHandle(xTask);uxReturn = pxTCB->uxPriority;}taskEXIT_CRITICAL();return uxReturn; } /* 在中斷中獲取任務優先級 */ UBaseType_t uxTaskPriorityGetFromISR(const TaskHandle_t xTask) {TCB_t const *pxTCB;UBaseType_t uxReturn, uxSavedInterruptState;portASSERT_IF_INTERRUPT_PRIORITY_INVALID();uxSavedInterruptState = portSET_INTERRUPT_MASK_FROM_ISR();{pxTCB = prvGetTCBFromHandle(xTask);uxReturn = pxTCB->uxPriority;}portCLEAR_INTERRUPT_MASK_FROM_ISR(uxSavedInterruptState);return uxReturn; }

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