F8 原碼分析

1.多任務特性

1.1任務調度機制

• 時間片任務調度機制:全部任務優先級相同,給每一個任務分配一個時間片,該任務在指定時間片內部執行
• 前面在配置的時候有一個任務優先級數量的概念,即configMAX_PRIORITIES,該數量受MCU內存限制,數量越多,佔用內存越高
• RTOS爲實時操做系統,因此必須支持搶佔,故產生了中斷優先級,高優先級任務會打斷低優先級任務的執行

1.2任務狀態

• freeRTOS中大部分任務處於阻塞狀態

1.2任務優先級

• freeRTOS任務優先級越高,編號越高

2.任務實現

2.1函數原型

• cubeMX默認會建立一個任務
• 每個任務都是一個死循環
• 在任務裏面須要阻塞
• 任務不容許有返回值

void StartDefaultTask(void const * argument)
{
  for(;;)
  {
	  osDelay(1);
  }
}

2.2任務控制塊

• 任務控制塊就是描述任務屬性的結構體,包含如下東西

任務堆棧信息

任務調度信息

任務建立信息

任務通知信息

任務互斥信息

任務調試信息

• FreeRTOS的每個任務都有一些屬性須要存儲
• 將這些屬性集合到一塊兒用結構體表示
• 該結構體就叫任務控制塊(TCB_t)

選項	解釋
*pxTopOfStack	任務堆棧棧頂
xStateListltem	狀態列表項
xEventListltem	事件列表項
uxPriority	任務優先級
*pxStack	任務棧起始地址
pcTaskName[]	任務名稱
*pxEndOfStack	任務堆棧棧底

2.3任務句柄

• 一個指針,指向任務控制塊與任務指針

3.任務堆棧

3.1相關概念

• 保存現場:保存CPU寄存器與局部變量
• 堆棧單位:分配4字節爲單位(此處針對freeRTOS)
• 堆棧大小:每一個任務都須要本身的棧空間,應用不一樣,每一個任務須要的棧大小也是不一樣的

3.2堆棧大小如何肯定

• 函數嵌套:包含函數局部變量,函數形參,函數返回地址,函數內部狀態值
• 任務切換:全部寄存器都須要入棧,進入中斷會後其他通用寄存器和浮點寄存器入棧以及發生中斷嵌套都是用的系統棧
• 堆棧打印:測試每一個任務堆棧大小

3.3棧的理解

• 棧是一種數據結構
• 棧在物理上就是一塊物理內存
• 產生函數嵌套的時候就須要進行入棧與出棧操做,它用來保存程序執行的歷史
• 在操做系統裏面,每一個任務都有獨立的棧空間,用來保存任務的局部變量和一些寄存器信息

4.動態任務建立流程

4.1流程分析

• 分配任務控制塊內存空間
• 分配任務堆棧空間
• 初始化任務控制塊
• 初始化任務堆棧
• 添加任務到就緒列表中

4.2源碼分析

• 建立任務源碼

#if( configSUPPORT_DYNAMIC_ALLOCATION == 1 )

	BaseType_t xTaskCreate(	TaskFunction_t pxTaskCode,
							const char * const pcName,		/*lint !e971 Unqualified char types are allowed for strings and single characters only. */
							const configSTACK_DEPTH_TYPE usStackDepth,
							void * const pvParameters,
							UBaseType_t uxPriority,
							TaskHandle_t * const pxCreatedTask )
	{
	TCB_t *pxNewTCB;
	BaseType_t xReturn;

		/* If the stack grows down then allocate the stack then the TCB so the stack
		does not grow into the TCB.  Likewise if the stack grows up then allocate
		the TCB then the stack. */
		#if( portSTACK_GROWTH > 0 )
		{
			/* Allocate space for the TCB.  Where the memory comes from depends on
			the implementation of the port malloc function and whether or not static
			allocation is being used. */
			pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) );

			if( pxNewTCB != NULL )
			{
				/* Allocate space for the stack used by the task being created.
				The base of the stack memory stored in the TCB so the task can
				be deleted later if required. */
				pxNewTCB->pxStack = ( StackType_t * ) pvPortMalloc( ( ( ( size_t ) usStackDepth ) * sizeof( StackType_t ) ) ); /*lint !e961 MISRA exception as the casts are only redundant for some ports. */

				if( pxNewTCB->pxStack == NULL )
				{
					/* Could not allocate the stack.  Delete the allocated TCB. */
					vPortFree( pxNewTCB );
					pxNewTCB = NULL;
				}
			}
		}
		#else /* portSTACK_GROWTH */
		{
		StackType_t *pxStack;

			/* Allocate space for the stack used by the task being created. */
			pxStack = ( StackType_t * ) pvPortMalloc( ( ( ( size_t ) usStackDepth ) * sizeof( StackType_t ) ) ); /*lint !e961 MISRA exception as the casts are only redundant for some ports. */

			if( pxStack != NULL )
			{
				/* Allocate space for the TCB. */
				pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) ); /*lint !e961 MISRA exception as the casts are only redundant for some paths. */

				if( pxNewTCB != NULL )
				{
					/* Store the stack location in the TCB. */
					pxNewTCB->pxStack = pxStack;
				}
				else
				{
					/* The stack cannot be used as the TCB was not created.  Free
					it again. */
					vPortFree( pxStack );
				}
			}
			else
			{
				pxNewTCB = NULL;
			}
		}
		#endif /* portSTACK_GROWTH */

		if( pxNewTCB != NULL )
		{
			#if( tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE != 0 ) /*lint !e731 Macro has been consolidated for readability reasons. */
			{
				/* Tasks can be created statically or dynamically, so note this
				task was created dynamically in case it is later deleted. */
				pxNewTCB->ucStaticallyAllocated = tskDYNAMICALLY_ALLOCATED_STACK_AND_TCB;
			}
			#endif /* configSUPPORT_STATIC_ALLOCATION */
			/*初始化任務控制塊與堆棧*/
			prvInitialiseNewTask( pxTaskCode, pcName, ( uint32_t ) usStackDepth, pvParameters, uxPriority, pxCreatedTask, pxNewTCB, NULL );
            /*添加任務到就緒列表中*/
			prvAddNewTaskToReadyList( pxNewTCB );
			xReturn = pdPASS;
		}
		else
		{
			xReturn = errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY;
		}

		return xReturn;
	}

#endif /* configSUPPORT_DYNAMIC_ALLOCATION */

5.任務刪除流程

5.1流程分析

• 從就緒表中刪除
• 從事件表中刪除
• 釋聽任務控制塊
• 釋聽任務堆棧內存
• 開始任務調度

5.2源碼分析

void vTaskDelete( TaskHandle_t xTaskToDelete )
	{
	TCB_t *pxTCB;

		taskENTER_CRITICAL();
		{
			/* If null is passed in here then it is the calling task that is
			being deleted. */
			pxTCB = prvGetTCBFromHandle( xTaskToDelete );

			/* Remove task from the ready list. */
			if( uxListRemove( &( pxTCB->xStateListItem ) ) == ( UBaseType_t ) 0 )
			{
				taskRESET_READY_PRIORITY( pxTCB->uxPriority );
			}
			else
			{
				mtCOVERAGE_TEST_MARKER();
			}

			/* Is the task waiting on an event also? */
			if( listLIST_ITEM_CONTAINER( &( pxTCB->xEventListItem ) ) != NULL )
			{
				( void ) uxListRemove( &( pxTCB->xEventListItem ) );
			}
			else
			{
				mtCOVERAGE_TEST_MARKER();
			}

			/* Increment the uxTaskNumber also so kernel aware debuggers can
			detect that the task lists need re-generating.  This is done before
			portPRE_TASK_DELETE_HOOK() as in the Windows port that macro will
			not return. */
			uxTaskNumber++;

			if( pxTCB == pxCurrentTCB )
			{
				/* A task is deleting itself.  This cannot complete within the
				task itself, as a context switch to another task is required.
				Place the task in the termination list.  The idle task will
				check the termination list and free up any memory allocated by
				the scheduler for the TCB and stack of the deleted task. */
				vListInsertEnd( &xTasksWaitingTermination, &( pxTCB->xStateListItem ) );

				/* Increment the ucTasksDeleted variable so the idle task knows
				there is a task that has been deleted and that it should therefore
				check the xTasksWaitingTermination list. */
				++uxDeletedTasksWaitingCleanUp;

				/* The pre-delete hook is primarily for the Windows simulator,
				in which Windows specific clean up operations are performed,
				after which it is not possible to yield away from this task -
				hence xYieldPending is used to latch that a context switch is
				required. */
				portPRE_TASK_DELETE_HOOK( pxTCB, &xYieldPending );
			}
			else
			{
				--uxCurrentNumberOfTasks;
				prvDeleteTCB( pxTCB );

				/* Reset the next expected unblock time in case it referred to
				the task that has just been deleted. */
				prvResetNextTaskUnblockTime();
			}

			traceTASK_DELETE( pxTCB );
		}
		taskEXIT_CRITICAL();

		/* Force a reschedule if it is the currently running task that has just
		been deleted. */
		if( xSchedulerRunning != pdFALSE )
		{
			if( pxTCB == pxCurrentTCB )
			{
				configASSERT( uxSchedulerSuspended == 0 );
				portYIELD_WITHIN_API();
			}
			else
			{
				mtCOVERAGE_TEST_MARKER();
			}
		}
	}

6.任務掛起流程

6.1流程分析

• 從就緒列表中刪除
• 從事件列表中刪除
• 添加任務到掛起列表中
• 開始任務調度

6.2源碼分析

void vTaskSuspend( TaskHandle_t xTaskToSuspend )
	{
	TCB_t *pxTCB;

		taskENTER_CRITICAL();
		{
			/* If null is passed in here then it is the running task that is
			being suspended. */
			pxTCB = prvGetTCBFromHandle( xTaskToSuspend );

			traceTASK_SUSPEND( pxTCB );

			/* Remove task from the ready/delayed list and place in the
			suspended list. */
			if( uxListRemove( &( pxTCB->xStateListItem ) ) == ( UBaseType_t ) 0 )
			{
				taskRESET_READY_PRIORITY( pxTCB->uxPriority );
			}
			else
			{
				mtCOVERAGE_TEST_MARKER();
			}

			/* Is the task waiting on an event also? */
			if( listLIST_ITEM_CONTAINER( &( pxTCB->xEventListItem ) ) != NULL )
			{
				( void ) uxListRemove( &( pxTCB->xEventListItem ) );
			}
			else
			{
				mtCOVERAGE_TEST_MARKER();
			}

			vListInsertEnd( &xSuspendedTaskList, &( pxTCB->xStateListItem ) );

			#if( configUSE_TASK_NOTIFICATIONS == 1 )
			{
				if( pxTCB->ucNotifyState == taskWAITING_NOTIFICATION )
				{
					/* The task was blocked to wait for a notification, but is
					now suspended, so no notification was received. */
					pxTCB->ucNotifyState = taskNOT_WAITING_NOTIFICATION;
				}
			}
			#endif
		}
		taskEXIT_CRITICAL();

		if( xSchedulerRunning != pdFALSE )
		{
			/* Reset the next expected unblock time in case it referred to the
			task that is now in the Suspended state. */
			taskENTER_CRITICAL();
			{
				prvResetNextTaskUnblockTime();
			}
			taskEXIT_CRITICAL();
		}
		else
		{
			mtCOVERAGE_TEST_MARKER();
		}

		if( pxTCB == pxCurrentTCB )
		{
			if( xSchedulerRunning != pdFALSE )
			{
				/* The current task has just been suspended. */
				configASSERT( uxSchedulerSuspended == 0 );
				portYIELD_WITHIN_API();
			}
			else
			{
				/* The scheduler is not running, but the task that was pointed
				to by pxCurrentTCB has just been suspended and pxCurrentTCB
				must be adjusted to point to a different task. */
				if( listCURRENT_LIST_LENGTH( &xSuspendedTaskList ) == uxCurrentNumberOfTasks )
				{
					/* No other tasks are ready, so set pxCurrentTCB back to
					NULL so when the next task is created pxCurrentTCB will
					be set to point to it no matter what its relative priority
					is. */
					pxCurrentTCB = NULL;
				}
				else
				{
					vTaskSwitchContext();
				}
			}
		}
		else
		{
			mtCOVERAGE_TEST_MARKER();
		}
	}

7.任務恢復流程

7.1流程分析

• 從掛起列表中刪除
• 添加任務到就緒列表中
• 開始調度任務

7.2源碼分析

void vTaskResume( TaskHandle_t xTaskToResume )
	{
	TCB_t * const pxTCB = ( TCB_t * ) xTaskToResume;

		/* It does not make sense to resume the calling task. */
		configASSERT( xTaskToResume );

		/* The parameter cannot be NULL as it is impossible to resume the
		currently executing task. */
		if( ( pxTCB != NULL ) && ( pxTCB != pxCurrentTCB ) )
		{
			taskENTER_CRITICAL();
			{
				if( prvTaskIsTaskSuspended( pxTCB ) != pdFALSE )
				{
					traceTASK_RESUME( pxTCB );

					/* The ready list can be accessed even if the scheduler is
					suspended because this is inside a critical section. */
					( void ) uxListRemove(  &( pxTCB->xStateListItem ) );
					prvAddTaskToReadyList( pxTCB );

					/* A higher priority task may have just been resumed. */
					if( pxTCB->uxPriority >= pxCurrentTCB->uxPriority )
					{
						/* This yield may not cause the task just resumed to run,
						but will leave the lists in the correct state for the
						next yield. */
						taskYIELD_IF_USING_PREEMPTION();
					}
					else
					{
						mtCOVERAGE_TEST_MARKER();
					}
				}
				else
				{
					mtCOVERAGE_TEST_MARKER();
				}
			}
			taskEXIT_CRITICAL();
		}
		else
		{
			mtCOVERAGE_TEST_MARKER();
		}
	}

8.多任務啓動

8.1啓動流程

• 建立空閒任務
• 配置Systick,PendSV爲最低優先級
• 配置Systick寄存器
• 啓動第一個任務

8.2源碼分析

void vTaskStartScheduler( void )
{
BaseType_t xReturn;

	/* Add the idle task at the lowest priority. */
	#if( configSUPPORT_STATIC_ALLOCATION == 1 )
	{
		StaticTask_t *pxIdleTaskTCBBuffer = NULL;
		StackType_t *pxIdleTaskStackBuffer = NULL;
		uint32_t ulIdleTaskStackSize;

		/* The Idle task is created using user provided RAM - obtain the
		address of the RAM then create the idle task. */
		vApplicationGetIdleTaskMemory( &pxIdleTaskTCBBuffer, &pxIdleTaskStackBuffer, &ulIdleTaskStackSize );
        /*靜態建立空閒任務,此處配置任務控制塊*/
		xIdleTaskHandle = xTaskCreateStatic(	prvIdleTask,
												configIDLE_TASK_NAME,
												ulIdleTaskStackSize,
												( void * ) NULL, /*lint !e961.  The cast is not redundant for all compilers. */
												( tskIDLE_PRIORITY | portPRIVILEGE_BIT ),
												pxIdleTaskStackBuffer,
												pxIdleTaskTCBBuffer ); /*lint !e961 MISRA exception, justified as it is not a redundant explicit cast to all supported compilers. */
		/*判斷任務是否建立成功*/
		if( xIdleTaskHandle != NULL )
		{
			xReturn = pdPASS;
		}
		else
		{
			xReturn = pdFAIL;
		}
	}
	#else
	{
		/* The Idle task is being created using dynamically allocated RAM. */
		xReturn = xTaskCreate(	prvIdleTask,
								configIDLE_TASK_NAME,
								configMINIMAL_STACK_SIZE,
								( void * ) NULL,
								( tskIDLE_PRIORITY | portPRIVILEGE_BIT ),
								&xIdleTaskHandle ); /*lint !e961 MISRA exception, justified as it is not a redundant explicit cast to all supported compilers. */
	}
	#endif /* configSUPPORT_STATIC_ALLOCATION */
	/*是否建立軟件定時器*/
	#if ( configUSE_TIMERS == 1 )
	{
		if( xReturn == pdPASS )
		{
			xReturn = xTimerCreateTimerTask();
		}
		else
		{
			mtCOVERAGE_TEST_MARKER();
		}
	}
	#endif /* configUSE_TIMERS */

	if( xReturn == pdPASS )
	{
		/* freertos_tasks_c_additions_init() should only be called if the user
		definable macro FREERTOS_TASKS_C_ADDITIONS_INIT() is defined, as that is
		the only macro called by the function. */
		#ifdef FREERTOS_TASKS_C_ADDITIONS_INIT
		{
			freertos_tasks_c_additions_init();
		}
		#endif

		/* Interrupts are turned off here, to ensure a tick does not occur
		before or during the call to xPortStartScheduler().  The stacks of
		the created tasks contain a status word with interrupts switched on
		so interrupts will automatically get re-enabled when the first task
		starts to run. */
		portDISABLE_INTERRUPTS();

		#if ( configUSE_NEWLIB_REENTRANT == 1 )
		{
			/* Switch Newlib's _impure_ptr variable to point to the _reent
			structure specific to the task that will run first. */
			_impure_ptr = &( pxCurrentTCB->xNewLib_reent );
		}
		#endif /* configUSE_NEWLIB_REENTRANT */
        
		xNextTaskUnblockTime = portMAX_DELAY;
        /*開啓任務調度*/
		xSchedulerRunning = pdTRUE;
        /*Systick計數器置0*/
		xTickCount = ( TickType_t ) 0U;

		/* If configGENERATE_RUN_TIME_STATS is defined then the following
		macro must be defined to configure the timer/counter used to generate
		the run time counter time base.   NOTE:  If configGENERATE_RUN_TIME_STATS
		is set to 0 and the following line fails to build then ensure you do not
		have portCONFIGURE_TIMER_FOR_RUN_TIME_STATS() defined in your
		FreeRTOSConfig.h file. */
		portCONFIGURE_TIMER_FOR_RUN_TIME_STATS();

		/* Setting up the timer tick is hardware specific and thus in the
		portable interface. */
		if( xPortStartScheduler() != pdFALSE )
		{
			/* Should not reach here as if the scheduler is running the
			function will not return. */
		}
		else
		{
			/* Should only reach here if a task calls xTaskEndScheduler(). */
		}
	}
	else
	{
		/* This line will only be reached if the kernel could not be started,
		because there was not enough FreeRTOS heap to create the idle task
		or the timer task. */
		configASSERT( xReturn != errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY );
	}

	/* Prevent compiler warnings if INCLUDE_xTaskGetIdleTaskHandle is set to 0,
	meaning xIdleTaskHandle is not used anywhere else. */
	( void ) xIdleTaskHandle;
}


BaseType_t xPortStartScheduler( void )
{
	#if( configASSERT_DEFINED == 1 )
	{
		volatile uint32_t ulOriginalPriority;
		volatile uint8_t * const pucFirstUserPriorityRegister = ( uint8_t * ) ( portNVIC_IP_REGISTERS_OFFSET_16 + portFIRST_USER_INTERRUPT_NUMBER );
		volatile uint8_t ucMaxPriorityValue;

		/* Determine the maximum priority from which ISR safe FreeRTOS API
		functions can be called.  ISR safe functions are those that end in
		"FromISR".  FreeRTOS maintains separate thread and ISR API functions to
		ensure interrupt entry is as fast and simple as possible.

		Save the interrupt priority value that is about to be clobbered. */
		ulOriginalPriority = *pucFirstUserPriorityRegister;

		/* Determine the number of priority bits available.  First write to all
		possible bits. */
		*pucFirstUserPriorityRegister = portMAX_8_BIT_VALUE;

		/* Read the value back to see how many bits stuck. */
		ucMaxPriorityValue = *pucFirstUserPriorityRegister;

		/* The kernel interrupt priority should be set to the lowest
		priority. */
		configASSERT( ucMaxPriorityValue == ( configKERNEL_INTERRUPT_PRIORITY & ucMaxPriorityValue ) );

		/* Use the same mask on the maximum system call priority. */
		ucMaxSysCallPriority = configMAX_SYSCALL_INTERRUPT_PRIORITY & ucMaxPriorityValue;

		/* Calculate the maximum acceptable priority group value for the number
		of bits read back. */
		ulMaxPRIGROUPValue = portMAX_PRIGROUP_BITS;
		while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
		{
			ulMaxPRIGROUPValue--;
			ucMaxPriorityValue <<= ( uint8_t ) 0x01;
		}

		#ifdef __NVIC_PRIO_BITS
		{
			/* Check the CMSIS configuration that defines the number of
			priority bits matches the number of priority bits actually queried
			from the hardware. */
			configASSERT( ( portMAX_PRIGROUP_BITS - ulMaxPRIGROUPValue ) == __NVIC_PRIO_BITS );
		}
		#endif

		#ifdef configPRIO_BITS
		{
			/* Check the FreeRTOS configuration that defines the number of
			priority bits matches the number of priority bits actually queried
			from the hardware. */
			configASSERT( ( portMAX_PRIGROUP_BITS - ulMaxPRIGROUPValue ) == configPRIO_BITS );
		}
		#endif

		/* Shift the priority group value back to its position within the AIRCR
		register. */
		ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
		ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;

		/* Restore the clobbered interrupt priority register to its original
		value. */
		*pucFirstUserPriorityRegister = ulOriginalPriority;
	}
	#endif /* conifgASSERT_DEFINED */

	/* Make PendSV and SysTick the lowest priority interrupts. */
	portNVIC_SYSPRI2_REG |= portNVIC_PENDSV_PRI;
	portNVIC_SYSPRI2_REG |= portNVIC_SYSTICK_PRI;

	/* Start the timer that generates the tick ISR.  Interrupts are disabled
	here already. */
	vPortSetupTimerInterrupt();

	/* Initialise the critical nesting count ready for the first task. */
	uxCriticalNesting = 0;

	/* Start the first task. */
	prvStartFirstTask();

	/* Should not get here! */
	return 0;
}

/*初始化Systick值,即將其置0,系統上電的時候Systick的值並非0*/
void vPortSetupTimerInterrupt( void )
	{
		/* Calculate the constants required to configure the tick interrupt. */
		#if( configUSE_TICKLESS_IDLE == 1 )
		{
			ulTimerCountsForOneTick = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ );
			xMaximumPossibleSuppressedTicks = portMAX_24_BIT_NUMBER / ulTimerCountsForOneTick;
			ulStoppedTimerCompensation = portMISSED_COUNTS_FACTOR / ( configCPU_CLOCK_HZ / configSYSTICK_CLOCK_HZ );
		}
		#endif /* configUSE_TICKLESS_IDLE */

		/* Stop and clear the SysTick. */
		portNVIC_SYSTICK_CTRL_REG = 0UL;
		portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;

		/* Configure SysTick to interrupt at the requested rate. */
		portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
		portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );
	}

9.SVC啓動流程

• SVC也是一種異常,用於將用戶態切換爲內核態,相似於軟中斷,第一次切換任務

9.1業務流程

• 獲取當前任務棧頂
• 手動出棧r4-r11 r14
• 更新棧頂到PSP
• 使能全局中斷
• 調用異常返回指令

10.PendSV業務流程

• 搶佔調度任務

10.1業務流程

• 每產生一個Systick就會觸發一個PendSV異常
• 讀取當前PSP值
• 獲取當前任務棧頂
• 保存r4-r11 r14到當前棧中
• 更新棧頂到當前任務控制塊中
• 保存r3到棧
• 關閉中斷
• 查找優先級最高的任務
• 更新當前任務控制塊
• 開啓中斷
• 出棧r3值
• 出棧r4-r11,r14到當前棧中
• 更新棧頂到PSP
• 調用移除返回指令

11.Systick相關

11.1Systick初始化流程

• 配置SysTick裝載值
• 使能SysTick時鐘源
• 使能SysTick中斷
• 使能SysTick

11.2SysTick中斷服務函數

• 關閉中斷
• Tick值增長
• SysTick任務調度
• 啓動PendSV
• 開啓中斷

11.3SysTick任務調度

• 系統節拍數加1
• 判斷是否溢出
• 溢出更新任務鎖定時間
• 判斷是否有任務須要解除阻塞
• 獲取延時列表第一個任務控制塊(時間排序)
• 獲取狀態列表值,判斷時間是否到達,未到達退出
• 任務阻塞事件到達
• 從延時列表中刪除任務
• 從事件列表中刪除任務
• 添加到就緒列表
• 若是使用搶佔內核就判斷任務優先級是否大於當前任務優先級
• 開啓任務調度
• 若是使用時間片調度,判斷當前優先級下是否還有其餘任務
• 開啓任務調度

12.相對延時

12.1流程分析

• 掛起調度器,防止被其餘任務打斷
• 添加任務到延時列表
• 恢復調度器,進行上下文切換

12.2源碼分析

void vTaskDelay( const TickType_t xTicksToDelay )
	{
	BaseType_t xAlreadyYielded = pdFALSE;

		/* A delay time of zero just forces a reschedule. */
    	/*判斷延時時間是否大於0*/
		if( xTicksToDelay > ( TickType_t ) 0U )
		{
            /*斷言*/
			configASSERT( uxSchedulerSuspended == 0 );
            /*掛起調度器*/
			vTaskSuspendAll();
			{
				traceTASK_DELAY();

				/* A task that is removed from the event list while the
				scheduler is suspended will not get placed in the ready
				list or removed from the blocked list until the scheduler
				is resumed.

				This task cannot be in an event list as it is the currently
				executing task. */
				prvAddCurrentTaskToDelayedList( xTicksToDelay, pdFALSE );
			}
			xAlreadyYielded = xTaskResumeAll();
		}
		else
		{
			mtCOVERAGE_TEST_MARKER();
		}

		/* Force a reschedule if xTaskResumeAll has not already done so, we may
		have put ourselves to sleep. */
		if( xAlreadyYielded == pdFALSE )
		{
			portYIELD_WITHIN_API();
		}
		else
		{
			mtCOVERAGE_TEST_MARKER();
		}
	}

13.絕對延時

13.1流程分析

• 掛起調度器
• 判斷記錄的系統節拍值是否溢出,若是溢出,而且大於當前滴答值,那麼將當前任務添加到延時列表
• 判斷記錄的系統節拍值是否溢出,沒有溢出,當前定時間隔小於記錄值,或者大於系統節拍值,把當前任務添加到延時列表
• 更新記錄值,恢復調度器,進行上下文切換

13.2源碼分析

void vTaskDelayUntil( TickType_t * const pxPreviousWakeTime, const TickType_t xTimeIncrement )
	{
	TickType_t xTimeToWake;
	BaseType_t xAlreadyYielded, xShouldDelay = pdFALSE;
		/*斷言*/
		configASSERT( pxPreviousWakeTime );
		configASSERT( ( xTimeIncrement > 0U ) );
		configASSERT( uxSchedulerSuspended == 0 );

		vTaskSuspendAll();
		{
			/* Minor optimisation.  The tick count cannot change in this
			block. */
			const TickType_t xConstTickCount = xTickCount;

			/* Generate the tick time at which the task wants to wake. */
            /*獲取當前系統節拍值加初始記錄值*/
			xTimeToWake = *pxPreviousWakeTime + xTimeIncrement;

			if( xConstTickCount < *pxPreviousWakeTime )
			{
				/* The tick count has overflowed since this function was
				lasted called.  In this case the only time we should ever
				actually delay is if the wake time has also	overflowed,
				and the wake time is greater than the tick time.  When this
				is the case it is as if neither time had overflowed. */
				if( ( xTimeToWake < *pxPreviousWakeTime ) && ( xTimeToWake > xConstTickCount ) )
				{
					xShouldDelay = pdTRUE;
				}
				else
				{
					mtCOVERAGE_TEST_MARKER();
				}
			}
			else
			{
				/* The tick time has not overflowed.  In this case we will
				delay if either the wake time has overflowed, and/or the
				tick time is less than the wake time. */
				if( ( xTimeToWake < *pxPreviousWakeTime ) || ( xTimeToWake > xConstTickCount ) )
				{
					xShouldDelay = pdTRUE;
				}
				else
				{
					mtCOVERAGE_TEST_MARKER();
				}
			}

			/* Update the wake time ready for the next call. */
			*pxPreviousWakeTime = xTimeToWake;

			if( xShouldDelay != pdFALSE )
			{
				traceTASK_DELAY_UNTIL( xTimeToWake );

				/* prvAddCurrentTaskToDelayedList() needs the block time, not
				the time to wake, so subtract the current tick count. */
				prvAddCurrentTaskToDelayedList( xTimeToWake - xConstTickCount, pdFALSE );
			}
			else
			{
				mtCOVERAGE_TEST_MARKER();
			}
		}
		xAlreadyYielded = xTaskResumeAll();

		/* Force a reschedule if xTaskResumeAll has not already done so, we may
		have put ourselves to sleep. */
		if( xAlreadyYielded == pdFALSE )
		{
			portYIELD_WITHIN_API();
		}
		else
		{
			mtCOVERAGE_TEST_MARKER();
		}
	}

14.掛起調度器

14.1業務流程

• ++uxSchedulerSuspended,每掛起一次就加1
• 當它大於0時候表示禁止調度,等於0則打開調度(容許調度)

14.2源碼分析

void vTaskSuspendAll( void )
{
	/* A critical section is not required as the variable is of type
	BaseType_t.  Please read Richard Barry's reply in the following link to a
	post in the FreeRTOS support forum before reporting this as a bug! -
	http://goo.gl/wu4acr */
	++uxSchedulerSuspended;
}

15.恢復調度

15.1業務流程

• 進入臨界區(保護uxSchedulerSuspended資源),掛起記錄減1,相似於信號量的PV操做
• 判斷掛起就緒列表是否爲空;非空就添加任務到就緒列表中
• 若是優先級高於當前任務就進行上下文切換
• 判斷調度器掛起後的SysTick值,從新遍歷阻塞列表進行上下文切換

15.2源碼分析

BaseType_t xTaskResumeAll( void )
{
TCB_t *pxTCB = NULL;
BaseType_t xAlreadyYielded = pdFALSE;

	/* If uxSchedulerSuspended is zero then this function does not match a
	previous call to vTaskSuspendAll(). */
	configASSERT( uxSchedulerSuspended );

	/* It is possible that an ISR caused a task to be removed from an event
	list while the scheduler was suspended.  If this was the case then the
	removed task will have been added to the xPendingReadyList.  Once the
	scheduler has been resumed it is safe to move all the pending ready
	tasks from this list into their appropriate ready list. */
    /*進入臨界區*/
	taskENTER_CRITICAL();
	{
        /*uxSchedulerSuspended--*/
		--uxSchedulerSuspended;

		if( uxSchedulerSuspended == ( UBaseType_t ) pdFALSE )
		{
			if( uxCurrentNumberOfTasks > ( UBaseType_t ) 0U )
			{
				/* Move any readied tasks from the pending list into the
				appropriate ready list. */
				while( listLIST_IS_EMPTY( &xPendingReadyList ) == pdFALSE )
				{
					pxTCB = ( TCB_t * ) listGET_OWNER_OF_HEAD_ENTRY( ( &xPendingReadyList ) );
					( void ) uxListRemove( &( pxTCB->xEventListItem ) );
					( void ) uxListRemove( &( pxTCB->xStateListItem ) );
					prvAddTaskToReadyList( pxTCB );

					/* If the moved task has a priority higher than the current
					task then a yield must be performed. */
					if( pxTCB->uxPriority >= pxCurrentTCB->uxPriority )
					{
						xYieldPending = pdTRUE;
					}
					else
					{
						mtCOVERAGE_TEST_MARKER();
					}
				}

				if( pxTCB != NULL )
				{
					/* A task was unblocked while the scheduler was suspended,
					which may have prevented the next unblock time from being
					re-calculated, in which case re-calculate it now.  Mainly
					important for low power tickless implementations, where
					this can prevent an unnecessary exit from low power
					state. */
					prvResetNextTaskUnblockTime();
				}

				/* If any ticks occurred while the scheduler was suspended then
				they should be processed now.  This ensures the tick count does
				not	slip, and that any delayed tasks are resumed at the correct
				time. */
				{
					UBaseType_t uxPendedCounts = uxPendedTicks; /* Non-volatile copy. */

					if( uxPendedCounts > ( UBaseType_t ) 0U )
					{
						do
						{
							if( xTaskIncrementTick() != pdFALSE )
							{
								xYieldPending = pdTRUE;
							}
							else
							{
								mtCOVERAGE_TEST_MARKER();
							}
							--uxPendedCounts;
						} while( uxPendedCounts > ( UBaseType_t ) 0U );

						uxPendedTicks = 0;
					}
					else
					{
						mtCOVERAGE_TEST_MARKER();
					}
				}

				if( xYieldPending != pdFALSE )
				{
					#if( configUSE_PREEMPTION != 0 )
					{
						xAlreadyYielded = pdTRUE;
					}
					#endif
					taskYIELD_IF_USING_PREEMPTION();
				}
				else
				{
					mtCOVERAGE_TEST_MARKER();
				}
			}
		}
		else
		{
			mtCOVERAGE_TEST_MARKER();
		}
	}
	taskEXIT_CRITICAL();

	return xAlreadyYielded;
}

16.消息隊列建立

15.1業務流程

• pcHead,隊列頭指針
• pcTall,隊列尾指針
• pcWriteTo,當前要寫入的指針
• pcReadFrom,當前讀指針
• xTaskWaitingToSend,指向任務列表,參與系統調度
• xTaskWaitingToReceive
• uxMessagesWaiting,等待
• uxLength,成員長度
• uxItemSize,成員個數
• cRxLock.發送鎖
• cTxLock.接收鎖

15.2源碼分析

/*消息隊列可做爲信號量使用,故此處作了類型轉換*/
#define xQueueCreate( uxQueueLength, uxItemSize ) xQueueGenericCreate( ( uxQueueLength ), ( uxItemSize ), ( queueQUEUE_TYPE_BASE ) )



QueueHandle_t xQueueGenericCreate( const UBaseType_t uxQueueLength, const UBaseType_t uxItemSize, const uint8_t ucQueueType )
	{
	Queue_t *pxNewQueue;
	size_t xQueueSizeInBytes;
	uint8_t *pucQueueStorage;

		configASSERT( uxQueueLength > ( UBaseType_t ) 0 );

		if( uxItemSize == ( UBaseType_t ) 0 )
		{
			/* There is not going to be a queue storage area. */
			xQueueSizeInBytes = ( size_t ) 0;
		}
		else
		{
			/* Allocate enough space to hold the maximum number of items that
			can be in the queue at any time. */
			xQueueSizeInBytes = ( size_t ) ( uxQueueLength * uxItemSize ); /*lint !e961 MISRA exception as the casts are only redundant for some ports. */
		}
		/*分配空間*/
		pxNewQueue = ( Queue_t * ) pvPortMalloc( sizeof( Queue_t ) + xQueueSizeInBytes );

		if( pxNewQueue != NULL )
		{
			/* Jump past the queue structure to find the location of the queue
			storage area. */
			pucQueueStorage = ( ( uint8_t * ) pxNewQueue ) + sizeof( Queue_t );

			#if( configSUPPORT_STATIC_ALLOCATION == 1 )
			{
				/* Queues can be created either statically or dynamically, so
				note this task was created dynamically in case it is later
				deleted. */
				pxNewQueue->ucStaticallyAllocated = pdFALSE;
			}
			#endif /* configSUPPORT_STATIC_ALLOCATION */
			/*隊列初始化*/
			prvInitialiseNewQueue( uxQueueLength, uxItemSize, pucQueueStorage, ucQueueType, pxNewQueue );
		}
		else
		{
			traceQUEUE_CREATE_FAILED( ucQueueType );
		}

		return pxNewQueue;
	}

/*隊列初始化*/
static void prvInitialiseNewQueue( const UBaseType_t uxQueueLength, const UBaseType_t uxItemSize, uint8_t *pucQueueStorage, const uint8_t ucQueueType, Queue_t *pxNewQueue )
{
	/* Remove compiler warnings about unused parameters should
	configUSE_TRACE_FACILITY not be set to 1. */
	( void ) ucQueueType;

	if( uxItemSize == ( UBaseType_t ) 0 )
	{
		/* No RAM was allocated for the queue storage area, but PC head cannot
		be set to NULL because NULL is used as a key to say the queue is used as
		a mutex.  Therefore just set pcHead to point to the queue as a benign
		value that is known to be within the memory map. */
		pxNewQueue->pcHead = ( int8_t * ) pxNewQueue;
	}
	else
	{
		/* Set the head to the start of the queue storage area. */
		pxNewQueue->pcHead = ( int8_t * ) pucQueueStorage;
	}

	/* Initialise the queue members as described where the queue type is
	defined. */
	pxNewQueue->uxLength = uxQueueLength;
	pxNewQueue->uxItemSize = uxItemSize;
    /*重置隊列*/
	( void ) xQueueGenericReset( pxNewQueue, pdTRUE );

	#if ( configUSE_TRACE_FACILITY == 1 )
	{
		pxNewQueue->ucQueueType = ucQueueType;
	}
	#endif /* configUSE_TRACE_FACILITY */

	#if( configUSE_QUEUE_SETS == 1 )
	{
		pxNewQueue->pxQueueSetContainer = NULL;
	}
	#endif /* configUSE_QUEUE_SETS */

	traceQUEUE_CREATE( pxNewQueue );
}

/*重置隊列*/
BaseType_t xQueueGenericReset( QueueHandle_t xQueue, BaseType_t xNewQueue )
{
Queue_t * const pxQueue = ( Queue_t * ) xQueue;

	configASSERT( pxQueue );
	/*進入臨界區*/
	taskENTER_CRITICAL();
	{
        /*隊尾指針 = 隊頭指針 + 隊列程序控制塊大小*/
		pxQueue->pcTail = pxQueue->pcHead + ( pxQueue->uxLength * pxQueue->uxItemSize );
        /*置零*/
		pxQueue->uxMessagesWaiting = ( UBaseType_t ) 0U;
        /*將要操做的指針對象指向隊頭*/
		pxQueue->pcWriteTo = pxQueue->pcHead;
        /*將要讀取的地址指向隊尾*/
		pxQueue->u.pcReadFrom = pxQueue->pcHead + ( ( pxQueue->uxLength - ( UBaseType_t ) 1U ) * pxQueue->uxItemSize );
		pxQueue->cRxLock = queueUNLOCKED;
		pxQueue->cTxLock = queueUNLOCKED;

		if( xNewQueue == pdFALSE )
		{
			/* If there are tasks blocked waiting to read from the queue, then
			the tasks will remain blocked as after this function exits the queue
			will still be empty.  If there are tasks blocked waiting to write to
			the queue, then one should be unblocked as after this function exits
			it will be possible to write to it. */
			if( listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToSend ) ) == pdFALSE )
			{
				if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToSend ) ) != pdFALSE )
				{
					queueYIELD_IF_USING_PREEMPTION();
				}
				else
				{
					mtCOVERAGE_TEST_MARKER();
				}
			}
			else
			{
				mtCOVERAGE_TEST_MARKER();
			}
		}
		else
		{
			/* Ensure the event queues start in the correct state. */
            /*建立發送與接收節點*/
			vListInitialise( &( pxQueue->xTasksWaitingToSend ) );
			vListInitialise( &( pxQueue->xTasksWaitingToReceive ) );
		}
	}
    /*退出臨界區*/
	taskEXIT_CRITICAL();

	/* A value is returned for calling semantic consistency with previous
	versions. */
	return pdPASS;
}

17.消息隊列刪除

17.2源碼分析

void vQueueDelete( QueueHandle_t xQueue )
{
Queue_t * const pxQueue = ( Queue_t * ) xQueue;

	configASSERT( pxQueue );
	traceQUEUE_DELETE( pxQueue );

	#if ( configQUEUE_REGISTRY_SIZE > 0 )
	{
		vQueueUnregisterQueue( pxQueue );
	}
	#endif

	#if( ( configSUPPORT_DYNAMIC_ALLOCATION == 1 ) && ( configSUPPORT_STATIC_ALLOCATION == 0 ) )
	{
		/* The queue can only have been allocated dynamically - free it
		again. */
        /*直接釋放內存空間*/
		vPortFree( pxQueue );
	}
	#elif( ( configSUPPORT_DYNAMIC_ALLOCATION == 1 ) && ( configSUPPORT_STATIC_ALLOCATION == 1 ) )
	{
		/* The queue could have been allocated statically or dynamically, so
		check before attempting to free the memory. */
		if( pxQueue->ucStaticallyAllocated == ( uint8_t ) pdFALSE )
		{
            /*直接釋放內存空間*/
			vPortFree( pxQueue );
		}
		else
		{
			mtCOVERAGE_TEST_MARKER();
		}
	}
	#else
	{
		/* The queue must have been statically allocated, so is not going to be
		deleted.  Avoid compiler warnings about the unused parameter. */
		( void ) pxQueue;
	}
	#endif /* configSUPPORT_DYNAMIC_ALLOCATION */
}