freeRTOS源碼解析4--tasks.c 5

4.2.13 繼續任務--vTaskResume

介面：
void vTaskResume( TaskHandle_t xTaskToResume )
形參1：xTaskToResume ，想要繼續的任務handle；

首先是vTaskResume調用的一個內部函數：static BaseType_t prvTaskIsTaskSuspended( const TaskHandle_t xTask )，用於檢查任務是否是掛起狀態，只有掛起的任務才能繼續，否則是等待事件、通知等處於阻塞態，那就不能放到就緒列表，必須繼續等待。這個介面邏輯非常簡單，就直接看代碼即可。

 1 static BaseType_t prvTaskIsTaskSuspended( const TaskHandle_t xTask )
 2 {
 3     BaseType_t xReturn = pdFALSE;
 4     const TCB_t * const pxTCB = xTask;
 5 
 6     /* Accesses xPendingReadyList so must be called from a critical
 7      * section. */
 8 
 9     /* It does not make sense to check if the calling task is suspended. */
10     configASSERT( xTask );
11 
12     /* Is the task being resumed actually in the suspended list? */
13     /* 檢查任務是否在掛起列表, 不在則說明任務未掛起 */
14     if( listIS_CONTAINED_WITHIN( &xSuspendedTaskList, &( pxTCB->xStateListItem ) ) != pdFALSE )
15     {
16         /* Has the task already been resumed from within an ISR? */
17         /* 任務在掛起列表裡, 但在調度器暫停時被移至等待就緒列表中, 則說明任務未掛起 */
18         if( listIS_CONTAINED_WITHIN( &xPendingReadyList, &( pxTCB->xEventListItem ) ) == pdFALSE )
19         {
20             /* Is it in the suspended list because it is in the Suspended
21              * state, or because it is blocked with no timeout? */
22             /* 任務在掛起列表裡, 但在等待事件, 則說明任務未掛起 */
23             if( listIS_CONTAINED_WITHIN( NULL, &( pxTCB->xEventListItem ) ) != pdFALSE )
24             {
25                 #if ( configUSE_TASK_NOTIFICATIONS == 1 )
26                 {
27                     BaseType_t x;
28 
29                     /* The task does not appear on the event list item of
30                      * and of the RTOS objects, but could still be in the
31                      * blocked state if it is waiting on its notification
32                      * rather than waiting on an object.  If not, is
33                      * suspended. */
34                     /* 任務在掛起列表裡, 且未等待事件, 那麼如果在等待通知則未掛起, 否則掛起 */
35                     xReturn = pdTRUE;
36 
37                     for( x = ( BaseType_t ) 0; x < ( BaseType_t ) configTASK_NOTIFICATION_ARRAY_ENTRIES; x++ )
38                     {
39                         if( pxTCB->ucNotifyState[ x ] == taskWAITING_NOTIFICATION )
40                         {
41                             xReturn = pdFALSE;
42                             break;
43                         }
44                     }
45                 }
46                 #else /* if ( configUSE_TASK_NOTIFICATIONS == 1 ) */
47                 {
48                     xReturn = pdTRUE;
49                 }
50                 #endif /* if ( configUSE_TASK_NOTIFICATIONS == 1 ) */
51             }
52             else
53             {
54                 mtCOVERAGE_TEST_MARKER();
55             }
56         }
57         else
58         {
59             mtCOVERAGE_TEST_MARKER();
60         }
61     }
62     else
63     {
64         mtCOVERAGE_TEST_MARKER();
65     }
66 
67     /* 總結下來就是任務若在掛起列表裡, 如果不是在等待事件或通知, 則是掛起狀態, 否則不是 */
68 
69     return xReturn;
70 }

 1 void vTaskResume( TaskHandle_t xTaskToResume )
 2 {
 3     TCB_t * const pxTCB = xTaskToResume;
 4 
 5     /* It does not make sense to resume the calling task. */
 6     configASSERT( xTaskToResume );
 7 
 8     #if ( configNUMBER_OF_CORES == 1 )
 9         /* The parameter cannot be NULL as it is impossible to resume the
10          * currently executing task. */
11         if( ( pxTCB != pxCurrentTCB ) && ( pxTCB != NULL ) )
12     #endif
13     {
14         taskENTER_CRITICAL();
15         {
16             if( prvTaskIsTaskSuspended( pxTCB ) != pdFALSE )
17             {
18                 /* The ready list can be accessed even if the scheduler is
19                  * suspended because this is inside a critical section. */
20                 /* 只有任務處於掛起狀態才能繼續 */
21                 ( void ) uxListRemove( &( pxTCB->xStateListItem ) );
22                 prvAddTaskToReadyList( pxTCB );
23 
24                 /* This yield may not cause the task just resumed to run,
25                  * but will leave the lists in the correct state for the
26                  * next yield. */
27                 /* 保證各任務列表處於正常的狀態 */
28                 taskYIELD_ANY_CORE_IF_USING_PREEMPTION( pxTCB );
29             }
30             else
31             {
32                 mtCOVERAGE_TEST_MARKER();
33             }
34         }
35         taskEXIT_CRITICAL();
36     }
37     else
38     {
39         mtCOVERAGE_TEST_MARKER();
40     }
41 }

4.2.14 啟動調度--vTaskStartScheduler

 這個介面會創建空閑任務和軟定時器任務，之後就是允許第一個任務，這個介面永遠也不會返回，也是main中調用的最後一個介面。

 1 void vTaskStartScheduler( void )
 2 {
 3     BaseType_t xReturn;
 4 
 5     /* 創建空閑任務 */
 6     xReturn = prvCreateIdleTasks();
 7 
 8     #if ( configUSE_TIMERS == 1 )
 9     {
10         if( xReturn == pdPASS )
11         {
12             xReturn = xTimerCreateTimerTask();    // 創建軟定時器任務
13         }
14         else
15         {
16             mtCOVERAGE_TEST_MARKER();
17         }
18     }
19     #endif /* configUSE_TIMERS */
20 
21     if( xReturn == pdPASS )
22     {
23         /* Interrupts are turned off here, to ensure a tick does not occur
24          * before or during the call to xPortStartScheduler().  The stacks of
25          * the created tasks contain a status word with interrupts switched on
26          * so interrupts will automatically get re-enabled when the first task
27          * starts to run. */
28         /* 關閉中斷, 保證在調用xPortStartScheduler前不會發生tick中斷, 所有創建
29          * 的任務的棧中都包含一個中斷開啟的狀態字, 所以第一個任務運行時, 中斷
30          * 會自動開啟 */
31         /* 暫時沒看懂這個註釋的意思, 但這個介面只是設置了中斷優先順序屏蔽寄存器,
32          * 實際的中斷並未關閉, 系統中斷被屏蔽了 */
33         portDISABLE_INTERRUPTS();
34 
35         xNextTaskUnblockTime = portMAX_DELAY;
36         xSchedulerRunning = pdTRUE;
37         xTickCount = ( TickType_t ) configINITIAL_TICK_COUNT;
38 
39         /* If configGENERATE_RUN_TIME_STATS is defined then the following
40          * macro must be defined to configure the timer/counter used to generate
41          * the run time counter time base.   NOTE:  If configGENERATE_RUN_TIME_STATS
42          * is set to 0 and the following line fails to build then ensure you do not
43          * have portCONFIGURE_TIMER_FOR_RUN_TIME_STATS() defined in your
44          * FreeRTOSConfig.h file. */
45         portCONFIGURE_TIMER_FOR_RUN_TIME_STATS();
46 
47         /* Setting up the timer tick is hardware specific and thus in the
48          * portable interface. */
49 
50         /* The return value for xPortStartScheduler is not required
51          * hence using a void datatype. */
52         /* 真正的啟動調度器, 即啟動了第一個任務 */
53         ( void ) xPortStartScheduler();
54 
55         /* In most cases, xPortStartScheduler() will not return. If it
56          * returns pdTRUE then there was not enough heap memory available
57          * to create either the Idle or the Timer task. If it returned
58          * pdFALSE, then the application called xTaskEndScheduler().
59          * Most ports don't implement xTaskEndScheduler() as there is
60          * nothing to return to. */
61     }
62     else
63     {
64         /* This line will only be reached if the kernel could not be started,
65          * because there was not enough FreeRTOS heap to create the idle task
66          * or the timer task. */
67         configASSERT( xReturn != errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY );
68     }
69 
70     /* Prevent compiler warnings if INCLUDE_xTaskGetIdleTaskHandle is set to 0,
71      * meaning xIdleTaskHandles are not used anywhere else. */
72     ( void ) xIdleTaskHandles;
73 
74     /* OpenOCD makes use of uxTopUsedPriority for thread debugging. Prevent uxTopUsedPriority
75      * from getting optimized out as it is no longer used by the kernel. */
76     ( void ) uxTopUsedPriority;
77 }

4.2.15 停止調度--vTaskEndScheduler

這個介面和上一個相對，而且這個介面一定是在某個任務中調用的，因為系統不會主動停止調度器，而正常運行中始終只有某個任務和系統在運行，所以必然是某個任務主動調用的。

 1 void vTaskEndScheduler( void )
 2 {
 3     #if ( INCLUDE_vTaskDelete == 1 )
 4     {
 5         BaseType_t xCoreID;
 6 
 7         #if ( configUSE_TIMERS == 1 )
 8         {
 9             /* Delete the timer task created by the kernel. */
10             /* 刪除軟定時器任務 */
11             vTaskDelete( xTimerGetTimerDaemonTaskHandle() );
12         }
13         #endif /* #if ( configUSE_TIMERS == 1 ) */
14 
15         /* Delete Idle tasks created by the kernel.*/
16         for( xCoreID = 0; xCoreID < ( BaseType_t ) configNUMBER_OF_CORES; xCoreID++ )
17         {
18             vTaskDelete( xIdleTaskHandles[ xCoreID ] );    // 刪除空閑任務
19         }
20 
21         /* Idle task is responsible for reclaiming the resources of the tasks in
22          * xTasksWaitingTermination list. Since the idle task is now deleted and
23          * no longer going to run, we need to reclaim resources of all the tasks
24          * in the xTasksWaitingTermination list. */
25         /* 本應由空閑任務回收待刪除任務的資源, 但現在空閑任務被刪除了, 就在這裡處理 */
26         prvCheckTasksWaitingTermination();
27     }
28     #endif /* #if ( INCLUDE_vTaskDelete == 1 ) */
29 
30     /* Stop the scheduler interrupts and call the portable scheduler end
31      * routine so the original ISRs can be restored if necessary.  The port
32      * layer must ensure interrupts enable  bit is left in the correct state. */
33     /* 這跟啟動調度器時關中斷一樣的疑問 */
34     portDISABLE_INTERRUPTS();
35     xSchedulerRunning = pdFALSE;
36 
37     /* This function must be called from a task and the application is
38      * responsible for deleting that task after the scheduler is stopped. */
39     vPortEndScheduler();
40 }

　　好了，下一篇講xTaskAbortDelay和xTaskIncrementTick介面，這兩個介面較為複雜。

　　下篇再見。