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原创 FreeRTOS学习笔记

 2009-5-19 10:15  3275 5 6 分类: MCU/ 嵌入式

本次学习版本为5.2.0

*******************File:list.h & list.c*************************

1、几个重要的数据结构

struct xLIST_ITEM

{

portTickType xItemValue; /*< The value being listed. In most cases this is used to sort the list in descending order. */

volatile struct xLIST_ITEM * pxNext; /*< Pointer to the next xListItem in the list. */

volatile struct xLIST_ITEM * pxPrevious;/*< Pointer to the previous xListItem in the list. */

void * pvOwner; /*< Pointer to the object (normally a TCB) that contains the list item. There is therefore a two way link between the object containing the list item and the list item itself. */

void * pvContainer; /*< Pointer to the list in which this list item is placed (if any). */

};

typedef struct xLIST_ITEM xListItem; /* For some reason lint wants this as two separate definitions. */

xItemValue

* pxNext

* pxPrevious

* pvOwner

* pvContainer

xListItem的结构

struct xMINI_LIST_ITEM

{

portTickType xItemValue;

volatile struct xLIST_ITEM *pxNext;

volatile struct xLIST_ITEM *pxPrevious;

};

typedef struct xMINI_LIST_ITEM xMiniListItem;

typedef struct xLIST

{

volatile unsigned portBASE_TYPE uxNumberOfItems;

volatile xListItem * pxIndex; /*< Used to walk through the list. Points to the last item returned by a call to pvListGetOwnerOfNextEntry (). */

volatile xMiniListItem xListEnd; /*< List item that contains the maximum possible item value meaning it is always at the end of the list and is therefore used as a marker. */

} xList;

uxNumberOfItems

* pxIndex

xListEnd

xList的结构

xList是一个双向量表。xListEnd 只是作为一个标志，标志你此刻访问的是链表的尾部。它不存放有效的数据。它的next节点指向xList的头节点。

一个疑问：pxList->xListEnd.xItemValue到底做什么用？

2. 几个宏定义实现了对链表上节点的各种操作：

#define listSET_LIST_ITEM_OWNER( pxListItem, pxOwner ) ( pxListItem )->pvOwner = ( void * ) pxOwner

#define listSET_LIST_ITEM_VALUE( pxListItem, xValue ) ( pxListItem )->xItemValue = xValue

#define listGET_LIST_ITEM_VALUE( pxListItem ) ( ( pxListItem )->xItemValue )

#define listLIST_IS_EMPTY( pxList ) ( ( pxList )->uxNumberOfItems == ( unsigned portBASE_TYPE ) 0 )

#define listCURRENT_LIST_LENGTH( pxList ) ( ( pxList )->uxNumberOfItems )

#define listGET_OWNER_OF_NEXT_ENTRY( pxTCB, pxList )

#define listGET_OWNER_OF_HEAD_ENTRY( pxList ) ( ( pxList->uxNumberOfItems != ( unsigned portBASE_TYPE ) 0 ) ? ( (&( pxList->xListEnd ))->pxNext->pvOwner ) : ( NULL ) )

#define listIS_CONTAINED_WITHIN( pxList, pxListItem ) ( ( pxListItem )->pvContainer == ( void * ) pxList )

3.定义了几个链表操作函数：

void vListInitialise( xList *pxList );

void vListInitialiseItem( xListItem *pxItem );

void vListInsert( xList *pxList, xListItem *pxNewListItem ); 按照xListItem上的xItemValue值排序，然后插入。保证xItemValue是递增的。

void vListInsertEnd( xList *pxList, xListItem *pxNewListItem ); 直接插到pxList->index的后面。

void vListRemove( xListItem *pxItemToRemove );

*******************File:task.h & task.c*************************

1、任务控制块结构

typedef struct tskTaskControlBlock

{

volatile portSTACK_TYPE *pxTopOfStack; /*< Points to the location of the last item placed on the tasks stack. THIS MUST BE THE FIRST MEMBER OF THE STRUCT. */

xListItem xGenericListItem; /*< List item used to place the TCB in ready and blocked queues. */

xListItem xEventListItem; /*< List item used to place the TCB in event lists. */

unsigned portBASE_TYPE uxPriority; /*< The priority of the task where 0 is the lowest priority. */

portSTACK_TYPE *pxStack; /*< Points to the start of the stack. */

signed portCHAR pcTaskName[ configMAX_TASK_NAME_LEN ];/*< Descriptive name given to the task when created. Facilitates debugging only. */

#if ( portSTACK_GROWTH > 0 )

portSTACK_TYPE *pxEndOfStack; /*< Used for stack overflow checking on architectures where the stack grows up from low memory. */

#endif

#if ( portCRITICAL_NESTING_IN_TCB == 1 )

unsigned portBASE_TYPE uxCriticalNesting;

#endif

#if ( configUSE_TRACE_FACILITY == 1 )

unsigned portBASE_TYPE uxTCBNumber; /*< This is used for tracing the scheduler and making debugging easier only. */

#endif

#if ( configUSE_MUTEXES == 1 )

unsigned portBASE_TYPE uxBasePriority;

#endif

#if ( configUSE_APPLICATION_TASK_TAG == 1 )

pdTASK_HOOK_CODE pxTaskTag;

#endif

} tskTCB;

*pxTopOfStack

xGenericListItem

xEventListItem

uxPriority

*pxStack

pcTaskName

*pxEndOfStack

uxCriticalNesting

uxTCBNumber

uxBasePriority

pxTaskTag

任务控制块的结构

2、各个API函数。

/*-----------------------------------------------------------

* TASK CREATION API

*----------------------------------------------------------*/

portBASE_TYPE xTaskCreate(

pdTASK_CODE pvTaskCode,

const portCHAR * const pcName,

unsigned portSHORT usStackDepth,

void *pvParameters,

unsigned portBASE_TYPE uxPriority,

xTaskHandle *pvCreatedTask

);

void vTaskCode( void * pvParameters )

{

for( ;; )

{

// Task code goes here.

}

// Function that creates a task.

void vOtherFunction( void )

{

static unsigned char ucParameterToPass;

xTaskHandle xHandle;

// Create the task, storing the handle. Note that the passed parameter ucParameterToPass

// must exist for the lifetime of the task, so in this case is declared static. If it was just an

// an automatic stack variable it might no longer exist, or at least have been corrupted, by the time

// the new time attempts to access it.

xTaskCreate( vTaskCode, "NAME", STACK_SIZE, &ucParameterToPass, tskIDLE_PRIORITY, &xHandle );

// Use the handle to delete the task.

vTaskDelete( xHandle );

}

3、对于为什么要用到两个delaylist，我一直很不解。在vTaskIncrementTick（）函数中：

if( uxSchedulerSuspended == ( unsigned portBASE_TYPE ) pdFALSE )

{

++xTickCount;

if( xTickCount == ( portTickType ) 0 )

{

xList *pxTemp;

/* Tick count has overflowed so we need to swap the delay lists. XXXXXXXXXXXXXXXXXXXXXXXXXXXX

If there are any items in pxDelayedTaskList here then there is

an error! */

pxTemp = pxDelayedTaskList;

pxDelayedTaskList = pxOverflowDelayedTaskList;

pxOverflowDelayedTaskList = pxTemp;

xNumOfOverflows++;

}

/* See if this tick has made a timeout expire. */

prvCheckDelayedTasks();

}

明白是为什么了！因为FreeRTOS系统的时钟管理原理是，每发生一个始终节拍，xTimeCount加1.这样有一种可能是，xTimeCount会溢出。所以在挂起一个任务的时候，计算xTimeToWake值与xTimeCount的关系。如果大，则是计数器正常，任务进入pxDelayedTaskList里面。而如果小了，说明xTimeCount溢出了。则该任务要进入到pxOverflowDelayedTaskList里面。这样，随着时间节拍数的增加致溢出时，挂起队列自然而然要进行切换。这也是为什么学要两个delayedList的原因啦！

*******************File:queue.h & queue.c*************************

1、queue的结构定义。

typedef struct QueueDefinition

{

signed portCHAR *pcHead; /*< Points to the beginning of the queue storage area. */

signed portCHAR *pcTail; /*< Points to the byte at the end of the queue storage area. Once more byte is allocated than necessary to store the queue items, this is used as a marker. */

signed portCHAR *pcWriteTo; /*< Points to the free next place in the storage area. */

signed portCHAR *pcReadFrom; /*< Points to the last place that a queued item was read from. */

xList xTasksWaitingToSend; /*< List of tasks that are blocked waiting to post onto this queue. Stored in priority order. */

xList xTasksWaitingToReceive; /*< List of tasks that are blocked waiting to read from this queue. Stored in priority order. */

volatile unsigned portBASE_TYPE uxMessagesWaiting;/*< The number of items currently in the queue. */

unsigned portBASE_TYPE uxLength; /*< The length of the queue defined as the number of items it will hold, not the number of bytes. */

unsigned portBASE_TYPE uxItemSize; /*< The size of each items that the queue will hold. */

signed portBASE_TYPE xRxLock; /*< Stores the number of items received from the queue (removed from the queue) while the queue was locked. Set to queueUNLOCKED when the queue is not locked. */

signed portBASE_TYPE xTxLock; /*< Stores the number of items transmitted to the queue (added to the queue) while the queue was locked. Set to queueUNLOCKED when the queue is not locked. */

} xQUEUE;

*******************File:heap_2.c*************************

1、两个重要的数据结构

static struct xRTOS_HEAP

{

unsigned portLONG ulDummy;

unsigned portCHAR ucHeap[ configTOTAL_HEAP_SIZE ];

} xHeap;

typedef struct A_BLOCK_LINK

{

struct A_BLOCK_LINK *pxNextFreeBlock; /*<< The next free block in the list. */

size_t xBlockSize; /*<< The size of the free block. */