FreeRTOS学习记录 03--列表篇

0 前言

@ Author         ：Dargon
@ Record Date    ：2021/07/12
@ Reference Book : `FreeRTOS源码详解与应用开发`，`ARM Cortex-M3与Cortex-M4权威指南`，`B站正点原子FreeRTOS讲解视频`
@ Purpose        ：学习正点原子的miniFly，该飞控基于FreeRTOS系统开发的，所以学习一下记录下关于RTOS系统的一些基本操作，大概了解系统的工作原理，如何创建，运行，切换任务等等基本操作流程。在此进行学习的记录。

1 列表基础知识

1.1 列表List_t

• List_t 结构体定义

  typedef struct xLIST
  {
        
        
      listFIRST_LIST_INTEGRITY_CHECK_VALUE				/*< Set to a known value if configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
      configLIST_VOLATILE UBaseType_t uxNumberOfItems;
      ListItem_t * configLIST_VOLATILE pxIndex;			/*< Used to walk through the list.  Points to the last item returned by a call to listGET_OWNER_OF_NEXT_ENTRY (). */
      MiniListItem_t 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. */
      listSECOND_LIST_INTEGRITY_CHECK_VALUE				/*< Set to a known value if configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
  } List_t;
  

  1. uxNumberOfItems表示列表中列表项的个数
  2. pxIndex 用来遍历列表，一个列表项ListItem_t类型的指针
  3. xListEnd 用作一个标记，位于列表的末尾

1.2 列表项ListItem_t

• ListItem_t 结构体定义

  struct xLIST_ITEM
  {
        
        
      listFIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE			/*< Set to a known value if configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
      configLIST_VOLATILE TickType_t xItemValue;			/*< The value being listed.  In most cases this is used to sort the list in descending order. */
      struct xLIST_ITEM * configLIST_VOLATILE pxNext;		/*< Pointer to the next ListItem_t in the list. */
      struct xLIST_ITEM * configLIST_VOLATILE pxPrevious;	/*< Pointer to the previous ListItem_t 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 * configLIST_VOLATILE pvContainer;				/*< Pointer to the list in which this list item is placed (if any). */
      listSECOND_LIST_ITEM_INTEGRITY_CHECK_VALUE			/*< Set to a known value if configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
  };
  typedef struct xLIST_ITEM ListItem_t;					/* For some reason lint wants this as two separate definitions. */
  

  1. xItemValue表示该列表项的值
  2. pxNext 指向前一个列表项
  3. pxPrevious 指向后一个列表项
  4. pvOwner 指向所属于哪个任务块，对应于TBC_t 中的 xStateListItem->pvOwner
  5. pvContainer 指向当前所属于的列表

1.3 Mini列表项MiniListItem_t

• MiniListItem_t 结构体定义
  由于只用作列表的最后一项，只是做个标记而已，减少内存的浪费，简化的省略一些成员变量。

  struct xMINI_LIST_ITEM
  {
        
        
      listFIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE			/*< Set to a known value if configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
      configLIST_VOLATILE TickType_t xItemValue;
      struct xLIST_ITEM * configLIST_VOLATILE pxNext;
      struct xLIST_ITEM * configLIST_VOLATILE pxPrevious;
  };
  typedef struct xMINI_LIST_ITEM MiniListItem_t;
  

  1. xItemValue表示该列表项的值
  2. pxNext 指向前一个列表项
  3. pxPrevious 指向后一个列表项

2 API函数的实现

2.1 列表初始化 vListInitialise（）

• vListInitialise（） 初始化源码分析

  void vListInitialise( List_t * const pxList )
  {
        
        
      /* The list structure contains a list item which is used to mark the
      end of the list.  To initialise the list the list end is inserted
      as the only list entry. */
      pxList->pxIndex = ( ListItem_t * ) &( pxList->xListEnd );			/*lint !e826 !e740 The mini list structure is used as the list end to save RAM.  This is checked and valid. */
  
      /* The list end value is the highest possible value in the list to
      ensure it remains at the end of the list. */
      pxList->xListEnd.xItemValue = portMAX_DELAY;
  
      /* The list end next and previous pointers point to itself so we know
      when the list is empty. */
      pxList->xListEnd.pxNext = ( ListItem_t * ) &( pxList->xListEnd );	/*lint !e826 !e740 The mini list structure is used as the list end to save RAM.  This is checked and valid. */
      pxList->xListEnd.pxPrevious = ( ListItem_t * ) &( pxList->xListEnd );/*lint !e826 !e740 The mini list structure is used as the list end to save RAM.  This is checked and valid. */
  
      pxList->uxNumberOfItems = ( UBaseType_t ) 0U;
  
      /* Write known values into the list if
      configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
      listSET_LIST_INTEGRITY_CHECK_1_VALUE( pxList );
      listSET_LIST_INTEGRITY_CHECK_2_VALUE( pxList );
  }
  

  1. 将index 指向xListEnd
  2. 初始化 pxList->xListEnd.xItemValue = portMAX_DELAY;为最大值，确保在列表的末端
  3. 初始化 pxList->xListEnd.pxNext和 pxList->xListEnd.pxPrevious
  4. 初始化 pxList->uxNumberOfItems = ( UBaseType_t ) 0U; 列表项个数为0

2.2 列表项初始化 vListInitialiseItem（）

• vListInitialiseItem（）

  void vListInitialiseItem( ListItem_t * const pxItem )
  {
        
        
      /* Make sure the list item is not recorded as being on a list. */
      pxItem->pvContainer = NULL;
  
      /* Write known values into the list item if
      configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
      listSET_FIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE( pxItem );
      listSET_SECOND_LIST_ITEM_INTEGRITY_CHECK_VALUE( pxItem );
  }
  

  1. pxItem->pvContainer = NULL; 仅仅初始化次列表项的列表属性为 null

2.3 列表插入 vListInsert（）

• vListInsert（）
  1. 获取要插入的列表项的值
  2. 遍历列表，找到位置
  3. 更新next 和 previous
  4. 更新该插入列表值的pxNewListItem->pvContainer
  5. 列表 ( pxList->uxNumberOfItems )++;需要更新

2.4 列表末尾插入 vListInsertEnd（）

• vListInsertEnd（）

  	pxNewListItem->pxNext = pxIndex;
      pxNewListItem->pxPrevious = pxIndex->pxPrevious;
  
      /* Only used during decision coverage testing. */
      mtCOVERAGE_TEST_DELAY();
  
      pxIndex->pxPrevious->pxNext = pxNewListItem;
      pxIndex->pxPrevious = pxNewListItem;
  
      /* Remember which list the item is in. */
      pxNewListItem->pvContainer = ( void * ) pxList;
  
      ( pxList->uxNumberOfItems )++;
  

  1. 直接更新列表项的next 和previous即可

2.5 列表删除 uxListRemove（）

• uxListRemove（）

  UBaseType_t uxListRemove( ListItem_t * const pxItemToRemove )
  {
        
        
  /* The list item knows which list it is in.  Obtain the list from the list
  item. */
      List_t * const pxList = ( List_t * ) pxItemToRemove->pvContainer;
  
      pxItemToRemove->pxNext->pxPrevious = pxItemToRemove->pxPrevious;
      pxItemToRemove->pxPrevious->pxNext = pxItemToRemove->pxNext;
  
      /* Only used during decision coverage testing. */
      mtCOVERAGE_TEST_DELAY();
  
      /* Make sure the index is left pointing to a valid item. */
      if( pxList->pxIndex == pxItemToRemove )
      {
        
        
          pxList->pxIndex = pxItemToRemove->pxPrevious;
      }
      else
      {
        
        
          mtCOVERAGE_TEST_MARKER();
      }
  
      pxItemToRemove->pvContainer = NULL;
      ( pxList->uxNumberOfItems )--;
  
      return pxList->uxNumberOfItems;
  }
  

  1. 根据pxItemToRemove->pvContainer，获得所在的列表
  2. 进行更新next 和 previous
  3. 若是当前的index 指向的是被删除的，则进行更新到指向被删除的前一个列表项
  4. 更新列表项的个数( pxList->uxNumberOfItems )–;