1 FreeRTOS源码下载地址

https://www.freertos.org/
在这里插入图片描述

2 任务控制块TCB

2.1 任务控制块TCB

2.1.1 任务控制块的关键成员

volatile StackType_t * pxTopOfStack，上下文切换的核心依赖 —— 保存 / 恢复任务运行状态（如 CPU 寄存器值压栈 / 出栈）。指向任务栈中 “最后一个被使用的位置”（栈顶），存储任务当前的上下文（如寄存器值、返回地址等）。
UBaseType_t uxCoreAffinityMask，条件编译：（configUSE_CORE_AFFINITY == 1 && configNUMBER_OF_CORES > 1）在多核系统中，指定任务可运行的核心（核心亲和性）。
ListItem_t xStateListItem，将任务链接到 FreeRTOS 的 “状态链表” 中（如就绪链表、阻塞链表、挂起链表）。
ListItem_t xEventListItem，将任务链接到 “事件等待链表” 中（如信号量、消息队列、事件组的等待链表）。当任务调用xSemaphoreTake()、xQueueReceive()等函数等待事件时，会通过xEventListItem加入对应事件的等待链表，直到事件触发（如信号量被释放）才被移回就绪链表。
UBaseType_t uxPriority，存储任务的优先级（0 为最低优先级，最大值由configMAX_PRIORITIES定义）。
StackType_t * pxStack，指向任务栈的 “起始地址”（栈的最低地址，与pxTopOfStack配合标识栈的范围）。
- 与pxTopOfStack的关系：
  - pxStack：栈的起点（固定不变）；
  - pxTopOfStack：栈的当前顶部（随任务运行动态变化，如函数调用时栈顶上移）。
volatile BaseType_t xTaskRunState：标识任务的运行状态 —— 若任务正在运行，存储其所在的核心编号；若未运行，存储状态（如未运行、正在让出 CPU）。
UBaseType_t uxTaskAttributes：存储任务的属性，目前主要用于标识 “空闲任务”（FreeRTOS 为每个核心创建一个空闲任务，用于核心空闲时运行）。
char pcTaskName[ configMAX_TASK_NAME_LEN ]，存储任务的名称（字符串），仅用于调试（如通过vTaskList()打印任务列表时显示名称）。由configMAX_TASK_NAME_LEN定义（默认 16 字节，含终止符\0）。
UBaseType_t uxCriticalNesting，记录任务的 “临界区嵌套深度”（进入临界区时加 1，退出时减 1，0 表示不在临界区）。
UBaseType_t uxTCBNumber：存储 TCB 的创建序号（每次创建任务时递增），用于调试时识别任务是否被删除后重建（删除后重建的任务序号不同）。
UBaseType_t uxTaskNumber：供第三方跟踪工具使用，用于任务的唯一标识和性能分析。
UBaseType_t uxBasePriority：存储任务的 “基础优先级”（原始优先级），用于 “优先级继承” 机制 —— 当任务持有互斥锁时，若被高优先级任务等待，会临时提升到等待任务的优先级（避免优先级反转），释放锁后恢复为uxBasePriority。
UBaseType_t uxMutexesHeld：记录任务当前持有的互斥锁数量，用于确保任务删除时释放所有持有的锁（避免死锁）。

/** Task control block.  A task control block (TCB) is allocated for each task,* and stores task state information, including a pointer to the task's context* (the task's run time environment, including register values)*/
typedef struct tskTaskControlBlock       /* The old naming convention is used to prevent breaking kernel aware debuggers. */
{volatile StackType_t * pxTopOfStack; /**< Points to the location of the last item placed on the tasks stack.  THIS MUST BE THE FIRST MEMBER OF THE TCB STRUCT. */#if ( portUSING_MPU_WRAPPERS == 1 )xMPU_SETTINGS xMPUSettings; /**< The MPU settings are defined as part of the port layer.  THIS MUST BE THE SECOND MEMBER OF THE TCB STRUCT. */#endif#if ( configUSE_CORE_AFFINITY == 1 ) && ( configNUMBER_OF_CORES > 1 )UBaseType_t uxCoreAffinityMask; /**< Used to link the task to certain cores.  UBaseType_t must have greater than or equal to the number of bits as configNUMBER_OF_CORES. */#endifListItem_t xStateListItem;                  /**< The list that the state list item of a task is reference from denotes the state of that task (Ready, Blocked, Suspended ). */ListItem_t xEventListItem;                  /**< Used to reference a task from an event list. */UBaseType_t uxPriority;                     /**< The priority of the task.  0 is the lowest priority. */StackType_t * pxStack;                      /**< Points to the start of the stack. */#if ( configNUMBER_OF_CORES > 1 )volatile BaseType_t xTaskRunState;      /**< Used to identify the core the task is running on, if the task is running. Otherwise, identifies the task's state - not running or yielding. */UBaseType_t uxTaskAttributes;           /**< Task's attributes - currently used to identify the idle tasks. */#endifchar pcTaskName[ configMAX_TASK_NAME_LEN ]; /**< Descriptive name given to the task when created.  Facilitates debugging only. */#if ( configUSE_TASK_PREEMPTION_DISABLE == 1 )BaseType_t xPreemptionDisable; /**< Used to prevent the task from being preempted. */#endif#if ( ( portSTACK_GROWTH > 0 ) || ( configRECORD_STACK_HIGH_ADDRESS == 1 ) )StackType_t * pxEndOfStack; /**< Points to the highest valid address for the stack. */#endif#if ( portCRITICAL_NESTING_IN_TCB == 1 )UBaseType_t uxCriticalNesting; /**< Holds the critical section nesting depth for ports that do not maintain their own count in the port layer. */#endif#if ( configUSE_TRACE_FACILITY == 1 )UBaseType_t uxTCBNumber;  /**< Stores a number that increments each time a TCB is created.  It allows debuggers to determine when a task has been deleted and then recreated. */UBaseType_t uxTaskNumber; /**< Stores a number specifically for use by third party trace code. */#endif#if ( configUSE_MUTEXES == 1 )UBaseType_t uxBasePriority; /**< The priority last assigned to the task - used by the priority inheritance mechanism. */UBaseType_t uxMutexesHeld;#endif#if ( configUSE_APPLICATION_TASK_TAG == 1 )TaskHookFunction_t pxTaskTag;#endif#if ( configNUM_THREAD_LOCAL_STORAGE_POINTERS > 0 )void * pvThreadLocalStoragePointers[ configNUM_THREAD_LOCAL_STORAGE_POINTERS ];#endif#if ( configGENERATE_RUN_TIME_STATS == 1 )configRUN_TIME_COUNTER_TYPE ulRunTimeCounter; /**< Stores the amount of time the task has spent in the Running state. */#endif#if ( configUSE_C_RUNTIME_TLS_SUPPORT == 1 )configTLS_BLOCK_TYPE xTLSBlock; /**< Memory block used as Thread Local Storage (TLS) Block for the task. */#endif#if ( configUSE_TASK_NOTIFICATIONS == 1 )volatile uint32_t ulNotifiedValue[ configTASK_NOTIFICATION_ARRAY_ENTRIES ];volatile uint8_t ucNotifyState[ configTASK_NOTIFICATION_ARRAY_ENTRIES ];#endif/* See the comments in FreeRTOS.h with the definition of* tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE. */#if ( tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE != 0 )uint8_t ucStaticallyAllocated; /**< Set to pdTRUE if the task is a statically allocated to ensure no attempt is made to free the memory. */#endif#if ( INCLUDE_xTaskAbortDelay == 1 )uint8_t ucDelayAborted;#endif#if ( configUSE_POSIX_ERRNO == 1 )int iTaskErrno;#endif
} tskTCB;

2.1.2 TCB 的核心作用

TCB 是 FreeRTOS 任务的 “数字身份证”，通过整合栈信息、优先级、状态链表、同步机制等关键数据，实现了以下核心功能：

任务调度：操作系统通过uxPriority和xStateListItem选择下一个运行的任务；
上下文切换：依赖pxTopOfStack保存 / 恢复任务的运行环境；
任务同步：通过xEventListItem和任务通知成员实现任务间的事件交互；
内存与安全管理：通过 MPU 配置、栈溢出检测、临界区控制确保任务安全运行；
可扩展性：条件编译支持按需裁剪功能，适配从微控制器到多核处理器的各类场景。

2.2 ListItem_t

configLIST_VOLATILE TickType_t xItemValue;，节点的排序依据，通常存储任务的优先级、超时时间（如xTaskDelay()的延时值）等。
- FreeRTOS 通过该值对链表进行升序排序
  - 就绪任务链表按优先级（uxPriority）排序，高优先级任务排在前面；
  - 延时任务链表按唤醒时间（当前时间 + 延时值）排序，最早唤醒的任务排在最前。
双向链表指针，分别指向前驱节点和后继节点，形成双向链表结构。
- struct xLIST_ITEM * configLIST_VOLATILE pxNext;
- struct xLIST_ITEM * configLIST_VOLATILE pxPrevious;
void * pvOwner;，指向包含该链表节点的对象（通常是任务控制块TCB）。通过链表节点快速定位到所属任务。
struct xLIST * configLIST_VOLATILE pxContainer;，指向当前节点所在的链表（xLIST结构体）。

/** Definition of the only type of object that a list can contain.*/
struct xLIST;
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 ascending 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. */struct xLIST * configLIST_VOLATILE pxContainer;     /**< 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;

2.3 List_t

这个结构体是 FreeRTOS 内核中用于管理链表的核心数据结构xLIST。链表在 FreeRTOS 中被广泛用于任务调度、事件管理、资源分配等场景（如就绪任务链表、延时任务链表、信号量等待链表等）。

configLIST_VOLATILE UBaseType_t uxNumberOfItems;，记录链表中节点数量。
ListItem_t * configLIST_VOLATILE pxIndex;，用于迭代访问链表节点（支持循环遍历）。
MiniListItem_t xListEnd;，特殊节点，始终位于链表尾部，作为遍历终止标记。

/** Definition of the type of queue used by the scheduler.*/
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;

3 函数接口

3.1 vListInitialise

pxList->pxIndex = ( ListItem_t * ) &( pxList->xListEnd );，将遍历指针pxIndex指向哨兵节点xListEnd。空链表中没有有效节点，pxIndex指向尾部标记，确保首次遍历时能正确定位到第一个有效节点。
pxList->xListEnd.xItemValue = portMAX_DELAY;，将哨兵节点的xItemValue设为最大值（通常是0xFFFFFFFF）。在插入节点时，按xItemValue升序排列，哨兵节点的值最大，因此始终位于链表尾部，作为遍历终止标记。
pxList->xListEnd.pxNext = ( ListItem_t * ) &( pxList->xListEnd );，让哨兵节点的pxNext和pxPrevious都指向自身，形成自循环。
pxList->xListEnd.pxPrevious = ( ListItem_t * ) &( pxList->xListEnd );，让哨兵节点的pxNext和pxPrevious都指向自身，形成自循环。
pxList->uxNumberOfItems = ( UBaseType_t ) 0U;，将链表长度计数器置为 0，表示链表中没有有效节点。

void vListInitialise( List_t * const pxList )
{traceENTER_vListInitialise( 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 );listSET_FIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE( &( pxList->xListEnd ) );/* 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 );pxList->xListEnd.pxPrevious = ( ListItem_t * ) &( pxList->xListEnd );/* Initialize the remaining fields of xListEnd when it is a proper ListItem_t */#if ( configUSE_MINI_LIST_ITEM == 0 ){pxList->xListEnd.pvOwner = NULL;pxList->xListEnd.pxContainer = NULL;listSET_SECOND_LIST_ITEM_INTEGRITY_CHECK_VALUE( &( pxList->xListEnd ) );}#endifpxList->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 );traceRETURN_vListInitialise();
}

3.2 vListInitialiseItem

void vListInitialiseItem( ListItem_t * const pxItem )
{traceENTER_vListInitialiseItem( pxItem );/* Make sure the list item is not recorded as being on a list. */pxItem->pxContainer = 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 );traceRETURN_vListInitialiseItem();
}