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F8 原码分析

1.多任务特性

1.1任务调度机制

  • 时间片任务调度机制:所有任务优先级相同,给每个任务分配一个时间片,该任务在指定时间片内部执行
  • 前面在配置的时候有一个任务优先级数量的概念,即configMAX_PRIORITIES,该数量受MCU内存限制,数量越多,占用内存越高
  • RTOS为实时操作系统,所以必须支持抢占,故产生了中断优先级,高优先级任务会打断低优先级任务的执行

1.2任务状态

  • freeRTOS中大部分任务处于阻塞状态

F8 原码分析 _ JavaClub全栈架构师技术笔记

1.2任务优先级

  • freeRTOS任务优先级越高,编号越高

F8 原码分析 _ JavaClub全栈架构师技术笔记

2.任务实现

2.1函数原型

  • cubeMX默认会创建一个任务
  • 每一个任务都是一个死循环
  • 在任务里面需要阻塞
  • 任务不允许有返回值
void StartDefaultTask(void const * argument)
{
  for(;;)
  {
	  osDelay(1);
  }
}

2.2任务控制块

  • 任务控制块就是描述任务属性的结构体,包含以下东西

任务堆栈信息

任务调度信息

任务创建信息

任务通知信息

任务互斥信息

任务调试信息

  • FreeRTOS的每一个任务都有一些属性需要存储
  • 将这些属性集合到一起用结构体表示
  • 该结构体就叫任务控制块(TCB_t)
选项 解释
*pxTopOfStack 任务堆栈栈顶
xStateListltem 状态列表项
xEventListltem 事件列表项
uxPriority 任务优先级
*pxStack 任务栈起始地址
pcTaskName[] 任务名称
*pxEndOfStack 任务堆栈栈底

2.3任务句柄

  • 一个指针,指向任务控制块与任务指针

3.任务堆栈

3.1相关概念

  • 保存现场:保存CPU寄存器与局部变量
  • 堆栈单位:分配4字节为单位(此处针对freeRTOS)
  • 堆栈大小:每个任务都需要自己的栈空间,应用不同,每个任务需要的栈大小也是不同的

3.2堆栈大小如何确定

  • 函数嵌套:包含函数局部变量,函数形参,函数返回地址,函数内部状态值
  • 任务切换:所有寄存器都需要入栈,进入中断会后其余通用寄存器和浮点寄存器入栈以及发生中断嵌套都是用的系统栈
  • 堆栈打印:测试每个任务堆栈大小

3.3栈的理解

  • 栈是一种数据结构
  • 栈在物理上就是一块物理内存
  • 产生函数嵌套的时候就需要进行入栈与出栈操作,它用来保存程序执行的历史
  • 在操作系统里面,每个任务都有独立的栈空间,用来保存任务的局部变量和一些寄存器信息

4.动态任务创建流程

4.1流程分析

  • 分配任务控制块内存空间
  • 分配任务堆栈空间
  • 初始化任务控制块
  • 初始化任务堆栈
  • 添加任务到就绪列表中

4.2源码分析

  • 创建任务源码
#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 */
			/*初始化任务控制块与堆栈*/
			prvInitialiseNewTask( pxTaskCode, pcName, ( uint32_t ) usStackDepth, pvParameters, uxPriority, pxCreatedTask, pxNewTCB, NULL );
            /*添加任务到就绪列表中*/
			prvAddNewTaskToReadyList( pxNewTCB );
			xReturn = pdPASS;
		}
		else
		{
			xReturn = errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY;
		}

		return xReturn;
	}

#endif /* configSUPPORT_DYNAMIC_ALLOCATION */

5.任务删除流程

5.1流程分析

  • 从就绪表中删除
  • 从事件表中删除
  • 释放任务控制块
  • 释放任务堆栈内存
  • 开始任务调度

5.2源码分析

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.任务挂起流程

6.1流程分析

  • 从就绪列表中删除
  • 从事件列表中删除
  • 添加任务到挂起列表中
  • 开始任务调度

6.2源码分析

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.任务恢复流程

7.1流程分析

  • 从挂起列表中删除
  • 添加任务到就绪列表中
  • 开始调度任务

7.2源码分析

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.多任务启动

8.1启动流程

  • 创建空闲任务
  • 配置Systick,PendSV为最低优先级
  • 配置Systick寄存器
  • 启动第一个任务

8.2源码分析

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 );
        /*静态创建空闲任务,此处配置任务控制块*/
		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. */
		/*判断任务是否创建成功*/
		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 */
	/*是否创建软件定时器*/
	#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;
        /*开启任务调度*/
		xSchedulerRunning = pdTRUE;
        /*Systick计数器置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,即将其置0,系统上电的时候Systick的值并不是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启动流程

  • SVC也是一种异常,用于将用户态切换为内核态,类似于软中断,第一次切换任务

9.1业务流程

  • 获取当前任务栈顶
  • 手动出栈r4-r11 r14
  • 更新栈顶到PSP
  • 使能全局中断
  • 调用异常返回指令

10.PendSV业务流程

  • 抢占调度任务

10.1业务流程

  • 每产生一个Systick就会触发一个PendSV异常
  • 读取当前PSP值
  • 获取当前任务栈顶
  • 保存r4-r11 r14到当前栈中
  • 更新栈顶到当前任务控制块中
  • 保存r3到栈
  • 关闭中断
  • 查找优先级最高的任务
  • 更新当前任务控制块
  • 开启中断
  • 出栈r3值
  • 出栈r4-r11,r14到当前栈中
  • 更新栈顶到PSP
  • 调用移除返回指令

11.Systick相关

11.1Systick初始化流程

  • 配置SysTick装载值
  • 使能SysTick时钟源
  • 使能SysTick中断
  • 使能SysTick

11.2SysTick中断服务函数

  • 关闭中断
  • Tick值增加
  • SysTick任务调度
  • 启动PendSV
  • 开启中断

11.3SysTick任务调度

  • 系统节拍数加1
  • 判断是否溢出
  • 溢出更新任务锁定时间
  • 判断是否有任务需要解除阻塞
  • 获取延时列表第一个任务控制块(时间排序)
  • 获取状态列表值,判断时间是否到达,未到达退出
  • 任务阻塞事件到达
  • 从延时列表中删除任务
  • 从事件列表中删除任务
  • 添加到就绪列表
  • 如果使用抢占内核就判断任务优先级是否大于当前任务优先级
  • 开启任务调度
  • 如果使用时间片调度,判断当前优先级下是否还有其他任务
  • 开启任务调度

12.相对延时

12.1流程分析

  • 挂起调度器,防止被其他任务打断
  • 添加任务到延时列表
  • 恢复调度器,进行上下文切换

12.2源码分析

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

		/* A delay time of zero just forces a reschedule. */
    	/*判断延时时间是否大于0*/
		if( xTicksToDelay > ( TickType_t ) 0U )
		{
            /*断言*/
			configASSERT( uxSchedulerSuspended == 0 );
            /*挂起调度器*/
			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.绝对延时

13.1流程分析

  • 挂起调度器
  • 判断记录的系统节拍值是否溢出,如果溢出,并且大于当前滴答值,那么将当前任务添加到延时列表
  • 判断记录的系统节拍值是否溢出,没有溢出,当前定时间隔小于记录值,或者大于系统节拍值,把当前任务添加到延时列表
  • 更新记录值,恢复调度器,进行上下文切换

13.2源码分析

void vTaskDelayUntil( TickType_t * const pxPreviousWakeTime, const TickType_t xTimeIncrement )
	{
	TickType_t xTimeToWake;
	BaseType_t xAlreadyYielded, xShouldDelay = pdFALSE;
		/*断言*/
		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. */
            /*获取当前系统节拍值加初始记录值*/
			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.挂起调度器

14.1业务流程

  • ++uxSchedulerSuspended,每挂起一次就加1
  • 当它大于0时候表示禁止调度,等于0则打开调度(允许调度)

14.2源码分析

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.恢复调度

15.1业务流程

  • 进入临界区(保护uxSchedulerSuspended资源),挂起记录减1,类似于信号量的PV操作
  • 判断挂起就绪列表是否为空;非空就添加任务到就绪列表中
  • 如果优先级高于当前任务就进行上下文切换
  • 判断调度器挂起后的SysTick值,重新遍历阻塞列表进行上下文切换

15.2源码分析

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. */
    /*进入临界区*/
	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.消息队列创建

15.1业务流程

  • pcHead,队列头指针
  • pcTall,队列尾指针
  • pcWriteTo,当前要写入的指针
  • pcReadFrom,当前读指针
  • xTaskWaitingToSend,指向任务列表,参与系统调度
  • xTaskWaitingToReceive
  • uxMessagesWaiting,等待
  • uxLength,成员长度
  • uxItemSize,成员个数
  • cRxLock.发送锁
  • cTxLock.接收锁

15.2源码分析

/*消息队列可作为信号量使用,故此处做了类型转换*/
#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. */
		}
		/*分配空间*/
		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 */
			/*队列初始化*/
			prvInitialiseNewQueue( uxQueueLength, uxItemSize, pucQueueStorage, ucQueueType, pxNewQueue );
		}
		else
		{
			traceQUEUE_CREATE_FAILED( ucQueueType );
		}

		return pxNewQueue;
	}

/*队列初始化*/
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;
    /*重置队列*/
	( 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 );
}

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

	configASSERT( pxQueue );
	/*进入临界区*/
	taskENTER_CRITICAL();
	{
        /*队尾指针 = 队头指针 + 队列程序控制块大小*/
		pxQueue->pcTail = pxQueue->pcHead + ( pxQueue->uxLength * pxQueue->uxItemSize );
        /*置零*/
		pxQueue->uxMessagesWaiting = ( UBaseType_t ) 0U;
        /*将要操作的指针对象指向队头*/
		pxQueue->pcWriteTo = pxQueue->pcHead;
        /*将要读取的地址指向队尾*/
		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. */
            /*创建发送与接收节点*/
			vListInitialise( &( pxQueue->xTasksWaitingToSend ) );
			vListInitialise( &( pxQueue->xTasksWaitingToReceive ) );
		}
	}
    /*退出临界区*/
	taskEXIT_CRITICAL();

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

17.消息队列删除

17.2源码分析

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. */
        /*直接释放内存空间*/
		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 )
		{
            /*直接释放内存空间*/
			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 */
}

作者:MHDSG
来源链接:https://www.cnblogs.com/Meiyangyang945/p/15106544.html

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