freeRTOS源码解析4--tasks.c 2

烯八 · 2025-6-8 13:00:28

4、tasks.c解析

时隔两年，还是决定继续把这个系统解析完成，有始有终。不过这次源码又从官网上下载了最新的，可能和我以前看的略有区别，但应该基本不影响理解。
接下来正式开始。

4.1.3 新增或是遗漏的两个宏

1 /* Returns pdTRUE if the task is actively running and not scheduled to yield. */
2 /* 如果任务正在运行并且没有被调度，则返回 TRUE。 */
3 #define taskTASK_IS_RUNNING( pxTCB ) ( ( ( pxTCB ) == pxCurrentTCB ) ? ( pdTRUE ) : ( pdFALSE ) )
4 #define taskTASK_IS_RUNNING_OR_SCHEDULED_TO_YIELD( pxTCB ) ( ( ( pxTCB ) == pxCurrentTCB ) ? ( pdTRUE ) : ( pdFALSE ) )

复制代码

4.2 接口解析

4.2.1 静态创建任务--xTaskCreateStatic

这个接口创建的任务，根据“FreeRTOS.h”文件的描述，当任务删除时，任务的栈和TCB都不能被释放。

1 /* 根据FreeRTOSConfig.h配置的不同结构体会有差异, 这是我的结果 */
2 struct xSTATIC_LIST_ITEM
3 {
4 TickType_t xDummy2;
5 void * pvDummy3[ 4 ];
6 };
7 typedef struct xSTATIC_LIST_ITEM StaticListItem_t;
8
9 /* 根据FreeRTOSConfig.h配置的不同结构体会有差异, 这是我的结果。
10 * configMAX_TASK_NAME_LEN = 16
11 * configTASK_NOTIFICATION_ARRAY_ENTRIES = 1 */
12 typedef struct xSTATIC_TCB {
13 void * pxDummy1;
14 StaticListItem_t xDummy3[ 2 ];
15 UBaseType_t uxDummy5;
16 void * pxDummy6;
17 uint8_t ucDummy7[ configMAX_TASK_NAME_LEN ];
18 UBaseType_t uxDummy12[ 2 ];
19 uint32_t ulDummy18[ configTASK_NOTIFICATION_ARRAY_ENTRIES ];
20 uint8_t ucDummy19[ configTASK_NOTIFICATION_ARRAY_ENTRIES ];
21 uint8_t uxDummy20;
22 } StaticTask_t;
23
24
25 static TCB_t * prvCreateStaticTask( TaskFunction_t pxTaskCode,
26 const char * const pcName,
27 const configSTACK_DEPTH_TYPE uxStackDepth,
28 void * const pvParameters,
29 UBaseType_t uxPriority,
30 StackType_t * const puxStackBuffer,
31 StaticTask_t * const pxTaskBuffer,
32 TaskHandle_t * const pxCreatedTask )
33 {
34 TCB_t * pxNewTCB;
35
36 configASSERT( puxStackBuffer != NULL );
37 configASSERT( pxTaskBuffer != NULL );
38
39 #if ( configASSERT_DEFINED == 1 )
40 {
41 /* Sanity check that the size of the structure used to declare a
42 * variable of type StaticTask_t equals the size of the real task
43 * structure. */
44 /* 确保静态的TCB和TCB_t大小是一致的，一般是一致的 */
45 volatile size_t xSize = sizeof( StaticTask_t );
46 configASSERT( xSize == sizeof( TCB_t ) );
47 ( void ) xSize; /* Prevent unused variable warning when configASSERT() is not used. */
48 }
49 #endif /* configASSERT_DEFINED */
50
51 if( ( pxTaskBuffer != NULL ) && ( puxStackBuffer != NULL ) )
52 {
53 /* The memory used for the task's TCB and stack are passed into this
54 * function - use them. */
55 /* MISRA Ref 11.3.1 [Misaligned access] */
56 /* More details at: https://github.com/FreeRTOS/FreeRTOS-Kernel/blob/main/MISRA.md#rule-113 */
57 /* coverity[misra_c_2012_rule_11_3_violation] */
58 pxNewTCB = ( TCB_t * ) pxTaskBuffer;
59 ( void ) memset( ( void * ) pxNewTCB, 0x00, sizeof( TCB_t ) );
60 pxNewTCB->pxStack = ( StackType_t * ) puxStackBuffer;
61
62 #if ( tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE != 0 )
63 {
64 /* Tasks can be created statically or dynamically, so note this
65 * task was created statically in case the task is later deleted. */
66 /* 标记任务是静态创建的 */
67 pxNewTCB->ucStaticallyAllocated = tskSTATICALLY_ALLOCATED_STACK_AND_TCB;
68 }
69 #endif /* tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE */
70
71 /* 初始化任务参数，后面会讲到 */
72 prvInitialiseNewTask( pxTaskCode, pcName, uxStackDepth, pvParameters, uxPriority, pxCreatedTask, pxNewTCB, NULL );
73 }
74 else
75 {
76 pxNewTCB = NULL;
77 }
78
79 return pxNewTCB;
80 }
81 /*-----------------------------------------------------------*/
82
83 /* pxTaskCode：任务入口；
84 * pcName：任务名称；
85 * uxStackDepth：任务栈深；
86 * pvParameters：任务形参；
87 * uxPriority：任务优先级；
88 * puxStackBuffer：任务栈，用户提供内存；
89 * pxTaskBuffer：任务TCB数据存放，用户提供内存。 */
90 TaskHandle_t xTaskCreateStatic( TaskFunction_t pxTaskCode,
91 const char * const pcName,
92 const configSTACK_DEPTH_TYPE uxStackDepth,
93 void * const pvParameters,
94 UBaseType_t uxPriority,
95 StackType_t * const puxStackBuffer,
96 StaticTask_t * const pxTaskBuffer )
97 {
98 TaskHandle_t xReturn = NULL;
99 TCB_t * pxNewTCB;
100
101 /* 设置任务，初始化参数 */
102 pxNewTCB = prvCreateStaticTask( pxTaskCode, pcName, uxStackDepth, pvParameters, uxPriority, puxStackBuffer, pxTaskBuffer, &xReturn );
103
104 if( pxNewTCB != NULL )
105 {
106 prvAddNewTaskToReadyList( pxNewTCB ); /* 加入到就绪列表中，后面会讲到 */
107 }
108 else
109 {
110 mtCOVERAGE_TEST_MARKER();
111 }
112
113 return xReturn;
114 }

复制代码

xTaskCreateStatic 4.2.2 动态创建任务--xTaskCreate

1 static TCB_t * prvCreateTask( TaskFunction_t pxTaskCode,
2 const char * const pcName,
3 const configSTACK_DEPTH_TYPE uxStackDepth,
4 void * const pvParameters,
5 UBaseType_t uxPriority,
6 TaskHandle_t * const pxCreatedTask )
7 {
8 TCB_t * pxNewTCB;
9
10
11 StackType_t * pxStack;
12
13 /* 在堆栈管理的文章中有介绍过，申请内存
14 * #define pvPortMallocStack pvPortMalloc
15 * #define vPortFreeStack vPortFree */
16 pxStack = pvPortMallocStack( ( ( ( size_t ) uxStackDepth ) * sizeof( StackType_t ) ) );
17
18 if( pxStack != NULL )
19 {
20 /* Allocate space for the TCB. */
21 pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) );
22
23 if( pxNewTCB != NULL )
24 {
25 ( void ) memset( ( void * ) pxNewTCB, 0x00, sizeof( TCB_t ) );
26
27 /* Store the stack location in the TCB. */
28 pxNewTCB->pxStack = pxStack;
29 }
30 else
31 {
32 /* The stack cannot be used as the TCB was not created. Free
33 * it again. */
34 vPortFreeStack( pxStack );
35 }
36 }
37 else
38 {
39 pxNewTCB = NULL;
40 }
41
42 if( pxNewTCB != NULL )
43 {
44 #if ( tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE != 0 )
45 {
46 /* Tasks can be created statically or dynamically, so note this
47 * task was created dynamically in case it is later deleted. */
48 /* 标记任务是动态创建的 */
49 pxNewTCB->ucStaticallyAllocated = tskDYNAMICALLY_ALLOCATED_STACK_AND_TCB;
50 }
51 #endif /* tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE */
52
53 /* 初始化任务参数，后面会讲到 */
54 prvInitialiseNewTask( pxTaskCode, pcName, uxStackDepth, pvParameters, uxPriority, pxCreatedTask, pxNewTCB, NULL );
55 }
56
57 return pxNewTCB;
58 }
59 /*-----------------------------------------------------------*/
60
61 /* 这里的形参就不介绍了，应该都比较清楚 */
62 BaseType_t xTaskCreate( TaskFunction_t pxTaskCode,
63 const char * const pcName,
64 const configSTACK_DEPTH_TYPE uxStackDepth,
65 void * const pvParameters,
66 UBaseType_t uxPriority,
67 TaskHandle_t * const pxCreatedTask )
68 {
69 TCB_t * pxNewTCB;
70 BaseType_t xReturn;
71
72 /* 设置任务，初始化参数 */
73 pxNewTCB = prvCreateTask( pxTaskCode, pcName, uxStackDepth, pvParameters, uxPriority, pxCreatedTask );
74
75 if( pxNewTCB != NULL )
76 {
77 prvAddNewTaskToReadyList( pxNewTCB ); /* 加入到就绪列表中，后面会讲到 */
78 xReturn = pdPASS;
79 }
80 else
81 {
82 xReturn = errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY;
83 }
84
85 return xReturn;
86 }

复制代码

xTaskCreate4.2.3 初始化任务--prvInitialiseNewTask

这个函数比较复杂，是在创建任务的时候调用的，基本逻辑比较清晰，去除了一些多核、MPU的代码就简化很多。有一些列表的值也许暂时不清楚为何如此设置，但到使用时应该就清楚这个初始值的含义了。

1 static void prvInitialiseNewTask( TaskFunction_t pxTaskCode,
2 const char * const pcName,
3 const configSTACK_DEPTH_TYPE uxStackDepth,
4 void * const pvParameters,
5 UBaseType_t uxPriority,
6 TaskHandle_t * const pxCreatedTask,
7 TCB_t * pxNewTCB,
8 const MemoryRegion_t * const xRegions )
9 {
10 StackType_t * pxTopOfStack;
11 UBaseType_t x;
12
13 /* Calculate the top of stack address. This depends on whether the stack
14 * grows from high memory to low (as per the 80x86) or vice versa.
15 * portSTACK_GROWTH is used to make the result positive or negative as required
16 * by the port. */
17 #if ( portSTACK_GROWTH < 0 )
18 {
19 /* 往前走4个字节，因为这个栈是先存值，再移动指针，所以需要确保栈顶指针指向栈空间的最后一个有效位置 */
20 pxTopOfStack = &( pxNewTCB->pxStack[ uxStackDepth - ( configSTACK_DEPTH_TYPE ) 1 ] );
21 /* 栈需要对齐 */
22 pxTopOfStack = ( StackType_t * ) ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack ) & ( ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) ) );
23
24 /* Check the alignment of the calculated top of stack is correct. */
25 configASSERT( ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack & ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) == 0U ) );
26 }
27 #endif
28
29 /* Store the task name in the TCB. */
30 if( pcName != NULL )
31 {
32 for( x = ( UBaseType_t ) 0; x < ( UBaseType_t ) configMAX_TASK_NAME_LEN; x++ )
33 {
34 pxNewTCB->pcTaskName[ x ] = pcName[ x ];
35
36 /* Don't copy all configMAX_TASK_NAME_LEN if the string is shorter than
37 * configMAX_TASK_NAME_LEN characters just in case the memory after the
38 * string is not accessible (extremely unlikely). */
39 if( pcName[ x ] == ( char ) 0x00 )
40 {
41 break;
42 }
43 else
44 {
45 mtCOVERAGE_TEST_MARKER();
46 }
47 }
48
49 /* Ensure the name string is terminated in the case that the string length
50 * was greater or equal to configMAX_TASK_NAME_LEN. */
51 pxNewTCB->pcTaskName[ configMAX_TASK_NAME_LEN - 1U ] = '\0';
52 }
53 else
54 {
55 mtCOVERAGE_TEST_MARKER();
56 }
57
58 /* This is used as an array index so must ensure it's not too large. */
59 configASSERT( uxPriority < configMAX_PRIORITIES );
60
61 if( uxPriority >= ( UBaseType_t ) configMAX_PRIORITIES )
62 {
63 uxPriority = ( UBaseType_t ) configMAX_PRIORITIES - ( UBaseType_t ) 1U;
64 }
65 else
66 {
67 mtCOVERAGE_TEST_MARKER();
68 }
69
70 pxNewTCB->uxPriority = uxPriority;
71 #if ( configUSE_MUTEXES == 1 )
72 {
73 pxNewTCB->uxBasePriority = uxPriority; /* 用于优先级继承机制 */
74 }
75 #endif /* configUSE_MUTEXES */
76
77 vListInitialiseItem( &( pxNewTCB->xStateListItem ) );
78 vListInitialiseItem( &( pxNewTCB->xEventListItem ) );
79
80 /* Set the pxNewTCB as a link back from the ListItem_t. This is so we can get
81 * back to the containing TCB from a generic item in a list. */
82 /* 设置ListItem_t的持有者，这样可以从Item处获取到TCB */
83 listSET_LIST_ITEM_OWNER( &( pxNewTCB->xStateListItem ), pxNewTCB );
84
85 /* Event lists are always in priority order. */
86 /* 事件列表总是按优先级排序，具体的可以等解析事件的时候再会过来看为什么这么设置 */
87 listSET_LIST_ITEM_VALUE( &( pxNewTCB->xEventListItem ), ( TickType_t ) configMAX_PRIORITIES - ( TickType_t ) uxPriority );
88 listSET_LIST_ITEM_OWNER( &( pxNewTCB->xEventListItem ), pxNewTCB );
89
90 /* Initialize the TCB stack to look as if the task was already running,
91 * but had been interrupted by the scheduler. The return address is set
92 * to the start of the task function. Once the stack has been initialised
93 * the top of stack variable is updated. */
94 #if ( portUSING_MPU_WRAPPERS == 0 )
95 {
96 /* If the port has capability to detect stack overflow,
97 * pass the stack end address to the stack initialization
98 * function as well. */
99 #if ( portHAS_STACK_OVERFLOW_CHECKING == 0 )
100 {
101 /* 初始化栈，伪造一个现场 */
102 pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters );
103 }
104 #endif /* portHAS_STACK_OVERFLOW_CHECKING */
105 }
106 #endif /* portUSING_MPU_WRAPPERS */
107
108 if( pxCreatedTask != NULL )
109 {
110 /* Pass the handle out in an anonymous way. The handle can be used to
111 * change the created task's priority, delete the created task, etc.*/
112 *pxCreatedTask = ( TaskHandle_t ) pxNewTCB;
113 }
114 else
115 {
116 mtCOVERAGE_TEST_MARKER();
117 }
118 }

复制代码

prvInitialiseNewTask4.2.4 加入到就绪列表--prvAddNewTaskToReadyList

1 static void prvAddNewTaskToReadyList( TCB_t * pxNewTCB )
2 {
3 /* Ensure interrupts don't access the task lists while the lists are being
4 * updated. */
5 /* 会操作任务列表，所以需要进入临界区，防止有系统中断打断 */
6 taskENTER_CRITICAL();
7 {
8 uxCurrentNumberOfTasks = ( UBaseType_t ) ( uxCurrentNumberOfTasks + 1U );
9
10 if( pxCurrentTCB == NULL )
11 {
12 /* There are no other tasks, or all the other tasks are in
13 * the suspended state - make this the current task. */
14 pxCurrentTCB = pxNewTCB;
15
16 if( uxCurrentNumberOfTasks == ( UBaseType_t ) 1 )
17 {
18 /* This is the first task to be created so do the preliminary
19 * initialisation required. We will not recover if this call
20 * fails, but we will report the failure. */
21 /* 第一个任务被创建，需要先初始化任务列表，具体流程后面会解析 */
22 prvInitialiseTaskLists();
23 }
24 else
25 {
26 mtCOVERAGE_TEST_MARKER();
27 }
28 }
29 else
30 {
31 /* If the scheduler is not already running, make this task the
32 * current task if it is the highest priority task to be created
33 * so far. */
34 /*
35 如果调度器未被运行且这是至今为止创建的最高优先级的任务，则把此任务作为当前任务 */
36 if( xSchedulerRunning == pdFALSE )
37 {
38 if( pxCurrentTCB->uxPriority <= pxNewTCB->uxPriority )
39 {
40 pxCurrentTCB = pxNewTCB;
41 }
42 else
43 {
44 mtCOVERAGE_TEST_MARKER();
45 }
46 }
47 else
48 {
49 mtCOVERAGE_TEST_MARKER();
50 }
51 }
52
53 uxTaskNumber++;
54
55 prvAddTaskToReadyList( pxNewTCB ); // 真正的操作列表，放进去
56
57 portSETUP_TCB( pxNewTCB );
58 }
59 taskEXIT_CRITICAL();
60
61 if( xSchedulerRunning != pdFALSE )
62 {
63 /* If the created task is of a higher priority than the current task
64 * then it should run now. */
65 /* 如果创建的任务优先级比当前任务高，则yield */
66 taskYIELD_ANY_CORE_IF_USING_PREEMPTION( pxNewTCB );
67 }
68 else
69 {
70 mtCOVERAGE_TEST_MARKER();
71 }
72 }

复制代码

prvAddNewTaskToReadyList4.2.5 初始化任务列表--prvInitialiseTaskLists

1 static void prvInitialiseTaskLists( void )
2 {
3 UBaseType_t uxPriority;
4
5 /* 初始化所有的任务列表，包括就绪、阻塞、停止列表等 */
6 for( uxPriority = ( UBaseType_t ) 0U; uxPriority < ( UBaseType_t ) configMAX_PRIORITIES; uxPriority++ )
7 {
8 vListInitialise( &( pxReadyTasksLists[ uxPriority ] ) );
9 }
10
11 vListInitialise( &xDelayedTaskList1 );
12 vListInitialise( &xDelayedTaskList2 );
13 vListInitialise( &xPendingReadyList );
14
15 #if ( INCLUDE_vTaskDelete == 1 )
16 {
17 vListInitialise( &xTasksWaitingTermination );
18 }
19 #endif /* INCLUDE_vTaskDelete */
20
21 #if ( INCLUDE_vTaskSuspend == 1 )
22 {
23 vListInitialise( &xSuspendedTaskList );
24 }
25 #endif /* INCLUDE_vTaskSuspend */
26
27 /* Start with pxDelayedTaskList using list1 and the pxOverflowDelayedTaskList
28 * using list2. */
29 pxDelayedTaskList = &xDelayedTaskList1;
30 pxOverflowDelayedTaskList = &xDelayedTaskList2;
31 }

复制代码

prvInitialiseTaskLists
　　补充一下流程图：

到这里，创建任务所涉及到的接口都已解析过了，可能还遗留有一些小问题，但我相信在后面的解析过程中，这些问题都会有所解答。
下次开始任务删除相关的接口解析了。

来源：程序园用户自行投稿发布，如果侵权，请联系站长删除
免责声明：如果侵犯了您的权益，请联系站长，我们会及时删除侵权内容，谢谢合作！

账号		自动登录	找回密码
密码			立即注册

freeRTOS源码解析4--tasks.c 2

相关帖子

浏览过的版块

签约作者

freeRTOS源码解析4--tasks.c 2

相关帖子

相关推荐

浏览过的版块

签约作者