freertos 任务创建 xTaskCreate xTaskGenericCreate 源代码分析
任务定义
//宏定义 任务创建函数 #define xTaskCreate( pvTaskCode, pcName, usStackDepth, pvParameters, uxPriority, pxCreatedTask ) xTaskGenericCreate( ( pvTaskCode ), ( pcName ), ( usStackDepth ), ( pvParameters ), ( uxPriority ), ( pxCreatedTask ), ( NULL ), ( NULL ) )
//任务 创建任务
signed portBASE_TYPE xTaskGenericCreate( pdTASK_CODE pxTaskCode,///指向任务的入口函数.
const signed char * const pcName, //描述任务的名字。主要便于调试
unsigned short usStackDepth, //指定任务堆栈的深度
void *pvParameters, //指针用于作为一个参数传向创建的任务
unsigned portBASE_TYPE uxPriority, //任务运行时的优先级
xTaskHandle *pxCreatedTask, //用于传出任务的句柄,在API对该创建出来的任务进行引用如改变任务优先级
portSTACK_TYPE *puxStackBuffer, //堆栈缓冲区
const xMemoryRegion * const xRegions /*缓存区*/ )
{
signed portBASE_TYPE xReturn;
tskTCB * pxNewTCB;
configASSERT( pxTaskCode );
configASSERT( ( ( uxPriority & ( ~portPRIVILEGE_BIT ) ) < configMAX_PRIORITIES ) );
/* 为TCB 和 堆栈分配空间 */
pxNewTCB = prvAllocateTCBAndStack( usStackDepth, puxStackBuffer );
if( pxNewTCB != NULL ) /* 如果 TCB 空间分配成功 */
{
portSTACK_TYPE *pxTopOfStack;
#if( portUSING_MPU_WRAPPERS == 1 )
/* Should the task be created in privileged mode? 特权模式 */
portBASE_TYPE xRunPrivileged;
if( ( uxPriority & portPRIVILEGE_BIT ) != 0U )
{
xRunPrivileged = pdTRUE;
}
else
{
xRunPrivileged = pdFALSE;
}
uxPriority &= ~portPRIVILEGE_BIT;
#endif /* portUSING_MPU_WRAPPERS == 1 */
/* 计算堆栈栈顶的位置 */
#if( portSTACK_GROWTH < 0 )
{
pxTopOfStack = pxNewTCB->pxStack + ( usStackDepth - ( unsigned short ) 1 );
/* pxStack 指向堆栈的起始地址 */
pxTopOfStack = ( portSTACK_TYPE * ) ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack ) & ( ( portPOINTER_SIZE_TYPE ) ~portBYTE_ALIGNMENT_MASK ) ); /*lint !e923 MISRA exception. Avoiding casts between pointers and integers is not practical. Size differences accounted for using portPOINTER_SIZE_TYPE type. */
/* 堆栈有地址对齐的要求 */
/*内存对齐 */
configASSERT( ( ( ( unsigned long ) pxTopOfStack & ( unsigned long ) portBYTE_ALIGNMENT_MASK ) == 0UL ) );
}
#else /* portSTACK_GROWTH */
{
pxTopOfStack = pxNewTCB->pxStack;
/* 新建的堆栈是空的，所以堆栈的栈顶就在起始地址处（正生堆栈）*/
/* 内存对齐 */
configASSERT( ( ( ( unsigned long ) pxNewTCB->pxStack & ( unsigned long ) portBYTE_ALIGNMENT_MASK ) == 0UL ) );
/* If we want to use stack checking on architectures that use
a positive stack growth direction then we also need to store the
other extreme of the stack space. */
/* 如果要做堆栈检查，就要知道堆栈的另一端界限在哪里 */
pxNewTCB->pxEndOfStack = pxNewTCB->pxStack + ( usStackDepth - 1 );
}
#endif /* portSTACK_GROWTH */
/* 设置 TCB 的各个部分 */
prvInitialiseTCBVariables( pxNewTCB, pcName, uxPriority, xRegions, usStackDepth );
/* 初始化堆栈，使得任务好像被中断函数中断了一样，中断返回地址就是任务的首地址 */
/*一旦被初始化堆栈顶部的堆栈变量将被更新。 */
/* 初始化任务堆栈，并将返回地址保存在tcb中的pxTopOfStack变量*/
#if( portUSING_MPU_WRAPPERS == 1 )
{
pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters, xRunPrivileged );
}
#else /* portUSING_MPU_WRAPPERS */
{
//汇编语言对堆栈进行初始化
pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters );
}
#endif /* portUSING_MPU_WRAPPERS */
if( ( void * ) pxCreatedTask != NULL ) //任务句柄
{
/* 返回任务的句柄 */
*pxCreatedTask = ( xTaskHandle ) pxNewTCB;
}
/*关中断*/
taskENTER_CRITICAL();
{ /*更新系统的任务数*/
uxCurrentNumberOfTasks++;
if( pxCurrentTCB == NULL )
{
/* 没有其他任务, 或者其他任务在挂起状态 设为当前任务 */
pxCurrentTCB = pxNewTCB;
if( uxCurrentNumberOfTasks == ( unsigned portBASE_TYPE ) 1 )
{
//这是第一个任务，初始化任务状态切换调度时使用的几个链表
prvInitialiseTaskLists();
}
}
else
{
/* 如果调度没有运行使得当前任务为最高级任务 */
if( xSchedulerRunning == pdFALSE )
{
if( pxCurrentTCB->uxPriority <= uxPriority )
{
pxCurrentTCB = pxNewTCB;
}
}
}
if( pxNewTCB->uxPriority > uxTopUsedPriority )
{
uxTopUsedPriority = pxNewTCB->uxPriority;
}
uxTaskNumber++;
#if ( configUSE_TRACE_FACILITY == 1 )
{
/* Add a counter into the TCB 仅仅为了追踪*/
pxNewTCB->uxTCBNumber = uxTaskNumber;
}
#endif /* configUSE_TRACE_FACILITY */
traceTASK_CREATE( pxNewTCB );
prvAddTaskToReadyList( pxNewTCB ); //添加到就绪链表中
xReturn = pdPASS;
portSETUP_TCB( pxNewTCB );
}
taskEXIT_CRITICAL();
}
else //分配失败
{
xReturn = errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY;
traceTASK_CREATE_FAILED(); //无定义
}
if( xReturn == pdPASS )
{
if( xSchedulerRunning != pdFALSE ) //切换状态
{
if( pxCurrentTCB->uxPriority < uxPriority )
{
portYIELD_WITHIN_API(); //保存现成，然后选择下一个任务
}
}
}
return xReturn;
}
进入临界区
#define taskENTER_CRITICAL() portENTER_CRITICAL()
#define portENTER_CRITICAL() vPortEnterCritical()
void vPortEnterCritical( void )
{
portDISABLE_INTERRUPTS();
uxCriticalNesting++;
}
#define portDISABLE_INTERRUPTS() vPortSetInterruptMask() 关中断
__asm void vPortSetInterruptMask( void )
{
PRESERVE8
push { r0 }
mov r0, #configMAX_SYSCALL_INTERRUPT_PRIORITY
msr basepri, r0
pop { r0 }
bx r14
}
//通过basepri 屏蔽所有中断
任务链表初始化prvInitialiseTaskLists
static void prvInitialiseTaskLists( void )
{
unsigned portBASE_TYPE uxPriority;
for( uxPriority = ( unsigned portBASE_TYPE ) 0U; uxPriority < ( unsigned portBASE_TYPE ) configMAX_PRIORITIES; uxPriority++ )
{
vListInitialise( &( pxReadyTasksLists[ uxPriority ] ) );//初始化就绪链表数组
}
vListInitialise( &xDelayedTaskList1 );//初始化延时链表1
vListInitialise( &xDelayedTaskList2 );//初始化延时列表2
vListInitialise( &xPendingReadyList );//初始化调度器挂起时就绪链表
#if ( INCLUDE_vTaskDelete == 1 )
{
vListInitialise( &xTasksWaitingTermination );//初始化被删除任务链表
}
#endif /* INCLUDE_vTaskDelete */
#if ( INCLUDE_vTaskSuspend == 1 )
{
vListInitialise( &xSuspendedTaskList );//初始化
}
#endif /* INCLUDE_vTaskSuspend */
/* Start with pxDelayedTaskList using list1 and the pxOverflowDelayedTaskList
using list2. */
pxDelayedTaskList = &xDelayedTaskList1;
pxOverflowDelayedTaskList = &xDelayedTaskList2;
}
链表初始化vListInitialise
void vListInitialise( xList * const pxList )
{
/* 列表结构包含了一个列项目 被用来标记一个列表的结尾
To initialise the list the list end is inserted
作为唯一列的输入. */
pxList->pxIndex = ( xListItem * ) &( pxList->xListEnd ); /*lint !e826 !e740 The mini list structure is used as the list end to save RAM. This is checked and valid. */
/* 列结束的值 是列表中可能的最高值 确保他能留在队列的最后*/
pxList->xListEnd.xItemValue = portMAX_DELAY;
/* 列尾的下一个和上一个指针指向他本身，当列是空时 */
pxList->xListEnd.pxNext = ( xListItem * ) &( 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 = ( xListItem * ) &( 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 = ( unsigned portBASE_TYPE ) 0U;
}
任务切换函数
#define portYIELD_WITHIN_API portYIELD
#define portYIELD() vPortYieldFromISR()
void vPortYieldFromISR( void ) //请求中断函数
{
/* Set a PendSV to request a context switch. */
*(portNVIC_INT_CTRL) = portNVIC_PENDSVSET;
}
内存分配
static tskTCB *prvAllocateTCBAndStack( unsigned short usStackDepth, portSTACK_TYPE *puxStackBuffer )
{
tskTCB *pxNewTCB;
/* 分配TCB内存*/
pxNewTCB = ( tskTCB * ) pvPortMalloc( sizeof( tskTCB ) );
if( pxNewTCB != NULL )
{
/* 分配任务 所需要的内存*/
pxNewTCB->pxStack = ( portSTACK_TYPE * ) pvPortMallocAligned( ( ( ( size_t )usStackDepth ) * sizeof( portSTACK_TYPE ) ), puxStackBuffer );
if( pxNewTCB->pxStack == NULL )
{
/*任务内存分配失败，删掉新分配的TCB内存*/
vPortFree( pxNewTCB );
pxNewTCB = NULL;
}
else
{
/* 为了调试的*/
memset( pxNewTCB->pxStack, tskSTACK_FILL_BYTE, usStackDepth * sizeof( portSTACK_TYPE ) );
}
}
return pxNewTCB; //返回新创建的任务
}
任务初始化
static void prvInitialiseTCBVariables( tskTCB *pxTCB, const signed char * const pcName, unsigned portBASE_TYPE uxPriority, const xMemoryRegion * const xRegions, unsigned short usStackDepth )
{
#if configMAX_TASK_NAME_LEN > 1
{
/* Don't bring strncpy into the build unnecessarily. */
strncpy( ( char * ) pxTCB->pcTaskName, ( const char * ) pcName, ( unsigned short ) configMAX_TASK_NAME_LEN );
}
#endif
pxTCB->pcTaskName[ ( unsigned short ) configMAX_TASK_NAME_LEN - ( unsigned short ) 1 ] = ( signed char ) '\0';
//确保任务优先级 不超过 定义的最大优先级
if( uxPriority >= configMAX_PRIORITIES )
{
uxPriority = configMAX_PRIORITIES - ( unsigned portBASE_TYPE ) 1U;
}
pxTCB->uxPriority = uxPriority;
#if ( configUSE_MUTEXES == 1 )
{
pxTCB->uxBasePriority = uxPriority;
}
#endif
vListInitialiseItem( &( pxTCB->xGenericListItem ) ); //初始化任务链表
vListInitialiseItem( &( pxTCB->xEventListItem ) ); //初始化事件链表
/* Set the pxTCB as a link back from the xListItem. This is so we can get
back to the containing TCB from a generic item in a list. */
listSET_LIST_ITEM_OWNER( &( pxTCB->xGenericListItem ), pxTCB );
/* Event lists are always in priority order. */
listSET_LIST_ITEM_VALUE( &( pxTCB->xEventListItem ), configMAX_PRIORITIES - ( portTickType ) uxPriority );
listSET_LIST_ITEM_OWNER( &( pxTCB->xEventListItem ), pxTCB );
#if ( portCRITICAL_NESTING_IN_TCB == 1 )
{
pxTCB->uxCriticalNesting = ( unsigned portBASE_TYPE ) 0;
}
#endif
#if ( configUSE_APPLICATION_TASK_TAG == 1 )
{
pxTCB->pxTaskTag = NULL;
}
#endif
#if ( configGENERATE_RUN_TIME_STATS == 1 )
{
pxTCB->ulRunTimeCounter = 0UL;
}
#endif
#if ( portUSING_MPU_WRAPPERS == 1 )
{
vPortStoreTaskMPUSettings( &( pxTCB->xMPUSettings ), xRegions, pxTCB->pxStack, usStackDepth );
}
#else
{
( void ) xRegions;
( void ) usStackDepth;
}
#endif
}
cpu寄存器初始化
portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE pxCode, void *pvParameters )
{
pxTopOfStack--;
*pxTopOfStack = portINITIAL_XPSR; /* xPSR */
pxTopOfStack--;
*pxTopOfStack = ( portSTACK_TYPE ) pxCode; /* PC */
pxTopOfStack--;
*pxTopOfStack = 0; /* LR */
pxTopOfStack -= 5; /* R12, R3, R2 and R1. */
*pxTopOfStack = ( portSTACK_TYPE ) pvParameters; /* R0 */
pxTopOfStack -= 8; /* R11, R10, R9, R8, R7, R6, R5 and R4. */
return pxTopOfStack;
}
添加任务定义
#define prvAddTaskToReadyQueue( pxTCB ) \
if( ( pxTCB )->uxPriority > uxTopReadyPriority ) \
{ \
uxTopReadyPriority = ( pxTCB )->uxPriority; \
} \
vListInsertEnd( ( xList * ) &( pxReadyTasksLists[ ( pxTCB )->uxPriority ] ), &( ( pxTCB )->xGenericListItem ) )