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1 FreeRTOS源码下载地址

https://www.freertos.org/

2 函数接口

2.1 函数接口

void vTaskStartScheduler( void )

2.2 函数参数简介

参数 - 无

3 vTaskDelete的调用关系

3.1 调用关系

|- vTaskStartScheduler|- prvCreateIdleTasks()|- xTaskCreate( pxIdleTaskFunction, ...)|- prvCreateTask|- pxStack = pvPortMallocStack( ( ( ( size_t ) uxStackDepth ) * sizeof( StackType_t ) ) );|- pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) );|- prvInitialiseNewTask|- vListInitialiseItem( &( pxNewTCB->xStateListItem ) );|- vListInitialiseItem( &( pxNewTCB->xEventListItem ) );|- pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters );|- *pxCreatedTask = ( TaskHandle_t ) pxNewTCB;|- prvAddNewTaskToReadyList|- prvInitialiseTaskLists|- prvAddTaskToReadyList|- listINSERT_END( &( pxReadyTasksLists[ ( pxTCB )->uxPriority ] ), &( ( pxTCB )->xStateListItem ) );|- xTimerCreateTimerTask()|- xTaskCreateAffinitySet|- prvCreateTask|- pxStack = pvPortMallocStack( ( ( ( size_t ) uxStackDepth ) * sizeof( StackType_t ) ) );|- pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) );|- prvInitialiseNewTask|- vListInitialiseItem( &( pxNewTCB->xStateListItem ) );|- vListInitialiseItem( &( pxNewTCB->xEventListItem ) );|- pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters );|- *pxCreatedTask = ( TaskHandle_t ) pxNewTCB;|- prvAddNewTaskToReadyList|- prvInitialiseTaskLists|- prvAddTaskToReadyList|- listINSERT_END( &( pxReadyTasksLists[ ( pxTCB )->uxPriority ] ), &( ( pxTCB )->xStateListItem ) )|- pxNewTCB->uxCoreAffinityMask = uxCoreAffinityMask;|- prvAddNewTaskToReadyList( pxNewTCB );|- xPortStartScheduler()|- vPortRestoreTaskContext|- portRESTORE_CONTEXT

3.2 调用关系示意图

4 函数源码分析

4.1 vTaskStartScheduler

• xReturn = prvCreateIdleTasks(); 创建idle线程
• xReturn = xTimerCreateTimerTask(); 创建timer线程
• xSchedulerRunning = pdTRUE; 将当前系统的运行状态设置为pdTRUE
• ( void ) xPortStartScheduler(); 开始调度，这个和当前处理器的架构相关的，和也栈结构的设置相关。

void vTaskStartScheduler( void )
{BaseType_t xReturn;traceENTER_vTaskStartScheduler();#if ( configUSE_CORE_AFFINITY == 1 ) && ( configNUMBER_OF_CORES > 1 ){/* Sanity check that the UBaseType_t must have greater than or equal to* the number of bits as confNUMBER_OF_CORES. */configASSERT( ( sizeof( UBaseType_t ) * taskBITS_PER_BYTE ) >= configNUMBER_OF_CORES );}#endif /* #if ( configUSE_CORE_AFFINITY == 1 ) && ( configNUMBER_OF_CORES > 1 ) */xReturn = prvCreateIdleTasks();#if ( configUSE_TIMERS == 1 ){if( xReturn == pdPASS ){xReturn = xTimerCreateTimerTask();}else{mtCOVERAGE_TEST_MARKER();}}#endif /* configUSE_TIMERS */if( xReturn == pdPASS ){/* freertos_tasks_c_additions_init() should only be called if the user* definable macro FREERTOS_TASKS_C_ADDITIONS_INIT() is defined, as that is* the only macro called by the function. */#ifdef FREERTOS_TASKS_C_ADDITIONS_INIT{freertos_tasks_c_additions_init();}#endif/* Interrupts are turned off here, to ensure a tick does not occur* before or during the call to xPortStartScheduler().  The stacks of* the created tasks contain a status word with interrupts switched on* so interrupts will automatically get re-enabled when the first task* starts to run. */portDISABLE_INTERRUPTS();#if ( configUSE_C_RUNTIME_TLS_SUPPORT == 1 ){/* Switch C-Runtime's TLS Block to point to the TLS* block specific to the task that will run first. */configSET_TLS_BLOCK( pxCurrentTCB->xTLSBlock );}#endifxNextTaskUnblockTime = portMAX_DELAY;xSchedulerRunning = pdTRUE;xTickCount = ( TickType_t ) configINITIAL_TICK_COUNT;/* If configGENERATE_RUN_TIME_STATS is defined then the following* macro must be defined to configure the timer/counter used to generate* the run time counter time base.   NOTE:  If configGENERATE_RUN_TIME_STATS* is set to 0 and the following line fails to build then ensure you do not* have portCONFIGURE_TIMER_FOR_RUN_TIME_STATS() defined in your* FreeRTOSConfig.h file. */portCONFIGURE_TIMER_FOR_RUN_TIME_STATS();traceTASK_SWITCHED_IN();traceSTARTING_SCHEDULER( xIdleTaskHandles );/* Setting up the timer tick is hardware specific and thus in the* portable interface. *//* The return value for xPortStartScheduler is not required* hence using a void datatype. */( void ) xPortStartScheduler();/* In most cases, xPortStartScheduler() will not return. If it* returns pdTRUE then there was not enough heap memory available* to create either the Idle or the Timer task. If it returned* pdFALSE, then the application called xTaskEndScheduler().* Most ports don't implement xTaskEndScheduler() as there is* nothing to return to. */}else{/* This line will only be reached if the kernel could not be started,* because there was not enough FreeRTOS heap to create the idle task* or the timer task. */configASSERT( xReturn != errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY );}/* Prevent compiler warnings if INCLUDE_xTaskGetIdleTaskHandle is set to 0,* meaning xIdleTaskHandles are not used anywhere else. */( void ) xIdleTaskHandles;/* OpenOCD makes use of uxTopUsedPriority for thread debugging. Prevent uxTopUsedPriority* from getting optimized out as it is no longer used by the kernel. */( void ) uxTopUsedPriority;traceRETURN_vTaskStartScheduler();
}

4.2 prvCreateIdleTasks

4.2.1 prvCreateIdleTasks

• for( xCoreID = ( BaseType_t ) 0; xCoreID < ( BaseType_t ) configNUMBER_OF_CORES; xCoreID++ ) 遍历所有的core，为所有的core 都创建对应的idle task，并将其加入到Ready列表。
• pxIdleTaskFunction = prvIdleTask; 对于主核core，设置当前idle任务的处理函数为prvIdleTask
• pxIdleTaskFunction = prvPassiveIdleTask; 对于从核，其idle task的处理函数为prvPassiveIdleTask
• 创建idle task

xReturn = xTaskCreate( pxIdleTaskFunction,cIdleName,configMINIMAL_STACK_SIZE,( void * ) NULL,portPRIVILEGE_BIT, /* In effect ( tskIDLE_PRIORITY | portPRIVILEGE_BIT ), but tskIDLE_PRIORITY is zero. */&xIdleTaskHandles[ xCoreID ] );

static BaseType_t prvCreateIdleTasks( void )
{BaseType_t xReturn = pdPASS;BaseType_t xCoreID;char cIdleName[ configMAX_TASK_NAME_LEN ];TaskFunction_t pxIdleTaskFunction = NULL;BaseType_t xIdleTaskNameIndex;for( xIdleTaskNameIndex = ( BaseType_t ) 0; xIdleTaskNameIndex < ( BaseType_t ) configMAX_TASK_NAME_LEN; xIdleTaskNameIndex++ ){cIdleName[ xIdleTaskNameIndex ] = configIDLE_TASK_NAME[ xIdleTaskNameIndex ];/* Don't copy all configMAX_TASK_NAME_LEN if the string is shorter than* configMAX_TASK_NAME_LEN characters just in case the memory after the* string is not accessible (extremely unlikely). */if( cIdleName[ xIdleTaskNameIndex ] == ( char ) 0x00 ){break;}else{mtCOVERAGE_TEST_MARKER();}}/* Add each idle task at the lowest priority. */for( xCoreID = ( BaseType_t ) 0; xCoreID < ( BaseType_t ) configNUMBER_OF_CORES; xCoreID++ ){#if ( configNUMBER_OF_CORES == 1 ){pxIdleTaskFunction = prvIdleTask;}#else /* #if (  configNUMBER_OF_CORES == 1 ) */{/* In the FreeRTOS SMP, configNUMBER_OF_CORES - 1 passive idle tasks* are also created to ensure that each core has an idle task to* run when no other task is available to run. */if( xCoreID == 0 ){pxIdleTaskFunction = prvIdleTask;}else{pxIdleTaskFunction = prvPassiveIdleTask;}}#endif /* #if (  configNUMBER_OF_CORES == 1 ) *//* Update the idle task name with suffix to differentiate the idle tasks.* This function is not required in single core FreeRTOS since there is* only one idle task. */#if ( configNUMBER_OF_CORES > 1 ){/* Append the idle task number to the end of the name if there is space. */if( xIdleTaskNameIndex < ( BaseType_t ) configMAX_TASK_NAME_LEN ){cIdleName[ xIdleTaskNameIndex ] = ( char ) ( xCoreID + '0' );/* And append a null character if there is space. */if( ( xIdleTaskNameIndex + 1 ) < ( BaseType_t ) configMAX_TASK_NAME_LEN ){cIdleName[ xIdleTaskNameIndex + 1 ] = '\0';}else{mtCOVERAGE_TEST_MARKER();}}else{mtCOVERAGE_TEST_MARKER();}}#endif /* if ( configNUMBER_OF_CORES > 1 ) */#if ( configSUPPORT_STATIC_ALLOCATION == 1 ){StaticTask_t * pxIdleTaskTCBBuffer = NULL;StackType_t * pxIdleTaskStackBuffer = NULL;configSTACK_DEPTH_TYPE uxIdleTaskStackSize;/* The Idle task is created using user provided RAM - obtain the* address of the RAM then create the idle task. */#if ( configNUMBER_OF_CORES == 1 ){vApplicationGetIdleTaskMemory( &pxIdleTaskTCBBuffer, &pxIdleTaskStackBuffer, &uxIdleTaskStackSize );}#else{if( xCoreID == 0 ){vApplicationGetIdleTaskMemory( &pxIdleTaskTCBBuffer, &pxIdleTaskStackBuffer, &uxIdleTaskStackSize );}else{vApplicationGetPassiveIdleTaskMemory( &pxIdleTaskTCBBuffer, &pxIdleTaskStackBuffer, &uxIdleTaskStackSize, ( BaseType_t ) ( xCoreID - 1 ) );}}#endif /* if ( configNUMBER_OF_CORES == 1 ) */xIdleTaskHandles[ xCoreID ] = xTaskCreateStatic( pxIdleTaskFunction,cIdleName,uxIdleTaskStackSize,( void * ) NULL,portPRIVILEGE_BIT, /* In effect ( tskIDLE_PRIORITY | portPRIVILEGE_BIT ), but tskIDLE_PRIORITY is zero. */pxIdleTaskStackBuffer,pxIdleTaskTCBBuffer );if( xIdleTaskHandles[ xCoreID ] != NULL ){xReturn = pdPASS;}else{xReturn = pdFAIL;}}#else /* if ( configSUPPORT_STATIC_ALLOCATION == 1 ) */{/* The Idle task is being created using dynamically allocated RAM. */xReturn = xTaskCreate( pxIdleTaskFunction,cIdleName,configMINIMAL_STACK_SIZE,( void * ) NULL,portPRIVILEGE_BIT, /* In effect ( tskIDLE_PRIORITY | portPRIVILEGE_BIT ), but tskIDLE_PRIORITY is zero. */&xIdleTaskHandles[ xCoreID ] );}#endif /* configSUPPORT_STATIC_ALLOCATION *//* Break the loop if any of the idle task is failed to be created. */if( xReturn != pdPASS ){break;}else{#if ( configNUMBER_OF_CORES == 1 ){mtCOVERAGE_TEST_MARKER();}#else{/* Assign idle task to each core before SMP scheduler is running. */xIdleTaskHandles[ xCoreID ]->xTaskRunState = xCoreID;pxCurrentTCBs[ xCoreID ] = xIdleTaskHandles[ xCoreID ];}#endif}}return xReturn;
}

4.2.2 xTaskCreate

xTaskCreate的处理流程可以参考FreeRTOS之xTaskCreate，其调用流程如下所示：

|- xTaskCreate|- prvCreateTask|- pxStack = pvPortMallocStack( ( ( ( size_t ) uxStackDepth ) * sizeof( StackType_t ) ) );|- pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) );|- prvInitialiseNewTask|- vListInitialiseItem( &( pxNewTCB->xStateListItem ) );|- vListInitialiseItem( &( pxNewTCB->xEventListItem ) );|- pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters );|- *pxCreatedTask = ( TaskHandle_t ) pxNewTCB;|- prvAddNewTaskToReadyList|- prvInitialiseTaskLists|- prvAddTaskToReadyList|- listINSERT_END( &( pxReadyTasksLists[ ( pxTCB )->uxPriority ] ), &( ( pxTCB )->xStateListItem ) );

4.3 xTimerCreateTimerTask

• 多核并设置亲和性：创建Timer 任务，同时做亲和性设置，该处理是在多核的情况下做的处理，如果是单核或者没有开启亲和性的配置则会调用xTaskCreate去创建Timer任务。

xReturn = xTaskCreateAffinitySet( prvTimerTask,configTIMER_SERVICE_TASK_NAME,configTIMER_TASK_STACK_DEPTH,NULL,( ( UBaseType_t ) configTIMER_TASK_PRIORITY ) | portPRIVILEGE_BIT,configTIMER_SERVICE_TASK_CORE_AFFINITY,&xTimerTaskHandle );

• 单核或者未开启亲和性设置：

xReturn = xTaskCreate( prvTimerTask,configTIMER_SERVICE_TASK_NAME,configTIMER_TASK_STACK_DEPTH,NULL,( ( UBaseType_t ) configTIMER_TASK_PRIORITY ) | portPRIVILEGE_BIT,&xTimerTaskHandle );

BaseType_t xTimerCreateTimerTask( void )
{BaseType_t xReturn = pdFAIL;traceENTER_xTimerCreateTimerTask();/* This function is called when the scheduler is started if* configUSE_TIMERS is set to 1.  Check that the infrastructure used by the* timer service task has been created/initialised.  If timers have already* been created then the initialisation will already have been performed. */prvCheckForValidListAndQueue();if( xTimerQueue != NULL ){#if ( ( configNUMBER_OF_CORES > 1 ) && ( configUSE_CORE_AFFINITY == 1 ) ){#if ( configSUPPORT_STATIC_ALLOCATION == 1 ){StaticTask_t * pxTimerTaskTCBBuffer = NULL;StackType_t * pxTimerTaskStackBuffer = NULL;configSTACK_DEPTH_TYPE uxTimerTaskStackSize;vApplicationGetTimerTaskMemory( &pxTimerTaskTCBBuffer, &pxTimerTaskStackBuffer, &uxTimerTaskStackSize );xTimerTaskHandle = xTaskCreateStaticAffinitySet( prvTimerTask,configTIMER_SERVICE_TASK_NAME,uxTimerTaskStackSize,NULL,( ( UBaseType_t ) configTIMER_TASK_PRIORITY ) | portPRIVILEGE_BIT,pxTimerTaskStackBuffer,pxTimerTaskTCBBuffer,configTIMER_SERVICE_TASK_CORE_AFFINITY );if( xTimerTaskHandle != NULL ){xReturn = pdPASS;}}#else /* if ( configSUPPORT_STATIC_ALLOCATION == 1 ) */{xReturn = xTaskCreateAffinitySet( prvTimerTask,configTIMER_SERVICE_TASK_NAME,configTIMER_TASK_STACK_DEPTH,NULL,( ( UBaseType_t ) configTIMER_TASK_PRIORITY ) | portPRIVILEGE_BIT,configTIMER_SERVICE_TASK_CORE_AFFINITY,&xTimerTaskHandle );}#endif /* configSUPPORT_STATIC_ALLOCATION */}#else /* #if ( ( configNUMBER_OF_CORES > 1 ) && ( configUSE_CORE_AFFINITY == 1 ) ) */{#if ( configSUPPORT_STATIC_ALLOCATION == 1 ){StaticTask_t * pxTimerTaskTCBBuffer = NULL;StackType_t * pxTimerTaskStackBuffer = NULL;configSTACK_DEPTH_TYPE uxTimerTaskStackSize;vApplicationGetTimerTaskMemory( &pxTimerTaskTCBBuffer, &pxTimerTaskStackBuffer, &uxTimerTaskStackSize );xTimerTaskHandle = xTaskCreateStatic( prvTimerTask,configTIMER_SERVICE_TASK_NAME,uxTimerTaskStackSize,NULL,( ( UBaseType_t ) configTIMER_TASK_PRIORITY ) | portPRIVILEGE_BIT,pxTimerTaskStackBuffer,pxTimerTaskTCBBuffer );if( xTimerTaskHandle != NULL ){xReturn = pdPASS;}}#else /* if ( configSUPPORT_STATIC_ALLOCATION == 1 ) */{xReturn = xTaskCreate( prvTimerTask,configTIMER_SERVICE_TASK_NAME,configTIMER_TASK_STACK_DEPTH,NULL,( ( UBaseType_t ) configTIMER_TASK_PRIORITY ) | portPRIVILEGE_BIT,&xTimerTaskHandle );}#endif /* configSUPPORT_STATIC_ALLOCATION */}#endif /* #if ( ( configNUMBER_OF_CORES > 1 ) && ( configUSE_CORE_AFFINITY == 1 ) ) */}else{mtCOVERAGE_TEST_MARKER();}configASSERT( xReturn );traceRETURN_xTimerCreateTimerTask( xReturn );return xReturn;
}

4.4 xTaskCreateAffinitySet

• pxNewTCB = prvCreateTask( pxTaskCode, pcName, uxStackDepth, pvParameters, uxPriority, pxCreatedTask ); 创建pcName任务，任务的处理函数为pxTaskCode；
• pxNewTCB->uxCoreAffinityMask = uxCoreAffinityMask; 将当前的任务绑定到指定的core上去处理。
• rvAddNewTaskToReadyList( pxNewTCB ); 将任务添加到Ready任务链表。

BaseType_t xTaskCreateAffinitySet( TaskFunction_t pxTaskCode,const char * const pcName,const configSTACK_DEPTH_TYPE uxStackDepth,void * const pvParameters,UBaseType_t uxPriority,UBaseType_t uxCoreAffinityMask,TaskHandle_t * const pxCreatedTask )
{TCB_t * pxNewTCB;BaseType_t xReturn;traceENTER_xTaskCreateAffinitySet( pxTaskCode, pcName, uxStackDepth, pvParameters, uxPriority, uxCoreAffinityMask, pxCreatedTask );pxNewTCB = prvCreateTask( pxTaskCode, pcName, uxStackDepth, pvParameters, uxPriority, pxCreatedTask );if( pxNewTCB != NULL ){/* Set the task's affinity before scheduling it. */pxNewTCB->uxCoreAffinityMask = uxCoreAffinityMask;prvAddNewTaskToReadyList( pxNewTCB );xReturn = pdPASS;}else{xReturn = errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY;}traceRETURN_xTaskCreateAffinitySet( xReturn );return xReturn;
}

4.5 xPortStartScheduler

该函数和具体的处理器架构以及其对应处理器的实现有关，下面以Cortex-R5的为例来介绍

• __asm volatile ( "MRS %0, APSR" : "=r" ( ulAPSR )::"memory" ); 读取APSR寄存器的状态值，用于后面，随后将处理器模式设置为System模式
• portCPU_IRQ_DISABLE(); disable IRQ
• configSETUP_TICK_INTERRUPT(); 开启Tick中断。
• vPortRestoreTaskContext(); 开启第一个任务的执行

BaseType_t xPortStartScheduler( void )
{uint32_t ulAPSR, ulCycles = 8; /* 8 bits per byte. */#if ( configASSERT_DEFINED == 1 ){volatile uint8_t ucOriginalPriority;volatile uint8_t * const pucFirstUserPriorityRegister = ( volatile uint8_t * const ) ( configINTERRUPT_CONTROLLER_BASE_ADDRESS + portINTERRUPT_PRIORITY_REGISTER_OFFSET );volatile uint8_t ucMaxPriorityValue;/** Determine how many priority bits are implemented in the GIC.* Save the interrupt priority value that is about to be clobbered.*/ucOriginalPriority = *pucFirstUserPriorityRegister;/** Determine the number of priority bits available.  First write to* all possible bits.*/*pucFirstUserPriorityRegister = portMAX_8_BIT_VALUE;/* Read the value back to see how many bits stuck. */ucMaxPriorityValue = *pucFirstUserPriorityRegister;/* Shift to the least significant bits. */while( ( ucMaxPriorityValue & portBIT_0_SET ) != portBIT_0_SET ){ucMaxPriorityValue >>= ( uint8_t ) 0x01;/** If ulCycles reaches 0 then ucMaxPriorityValue must have been* read as 0, indicating a misconfiguration.*/ulCycles--;if( ulCycles == 0 ){break;}}/** Sanity check configUNIQUE_INTERRUPT_PRIORITIES matches the read* value.*/configASSERT( ucMaxPriorityValue == portLOWEST_INTERRUPT_PRIORITY );/** Restore the clobbered interrupt priority register to its original* value.*/*pucFirstUserPriorityRegister = ucOriginalPriority;}#endif /* configASSERT_DEFINED *//** Only continue if the CPU is not in User mode.  The CPU must be in a* Privileged mode for the scheduler to start.*/__asm volatile ( "MRS %0, APSR" : "=r" ( ulAPSR )::"memory" );ulAPSR &= portAPSR_MODE_BITS_MASK;configASSERT( ulAPSR != portAPSR_USER_MODE );if( ulAPSR != portAPSR_USER_MODE ){/** Only continue if the binary point value is set to its lowest possible* setting.  See the comments in vPortValidateInterruptPriority() below for* more information.*/configASSERT( ( portICCBPR_BINARY_POINT_REGISTER & portBINARY_POINT_BITS ) <= portMAX_BINARY_POINT_VALUE );if( ( portICCBPR_BINARY_POINT_REGISTER & portBINARY_POINT_BITS ) <= portMAX_BINARY_POINT_VALUE ){/** Interrupts are turned off in the CPU itself to ensure tick does* not execute  while the scheduler is being started.  Interrupts are* automatically turned back on in the CPU when the first task starts* executing.*/portCPU_IRQ_DISABLE();/* Start the timer that generates the tick ISR. */configSETUP_TICK_INTERRUPT();/* Start the first task executing. */vPortRestoreTaskContext();}}/** Will only get here if vTaskStartScheduler() was called with the CPU in* a non-privileged mode or the binary point register was not set to its lowest* possible value.  prvTaskExitError() is referenced to prevent a compiler* warning about it being defined but not referenced in the case that the user* defines their own exit address.*/( void ) prvTaskExitError;return 0;
}

4.6 vPortRestoreTaskContext

• CPS #SYS_MODE 切换当前处理器的模式为SYS模式
• portRESTORE_CONTEXT 回复用户栈

/******************************************************************************* vPortRestoreTaskContext is used to start the scheduler.*****************************************************************************/
.type vPortRestoreTaskContext, %function
vPortRestoreTaskContext:/* Switch to system mode. */CPS     #SYS_MODEportRESTORE_CONTEXT

4.7 portRESTORE_CONTEXT

• 取第一个任务，获取其对应的任务TCB，然后通过TCB获取其栈顶。

    LDR     R0, pxCurrentTCBConstLDR     R1, [R0]LDR     SP, [R1]

• 恢复用户设置的critical section nesting depth

    LDR     R0, ulCriticalNestingConstPOP     {R1}STR     R1, [R0]

• 恢复用户栈POP {R0-R12, R14}

.macro portRESTORE_CONTEXT/* Set the SP to point to the stack of the task being restored. */LDR     R0, pxCurrentTCBConstLDR     R1, [R0]LDR     SP, [R1]#if defined( __ARM_FP )/** Is there a floating point context to restore?  If the restored* ulPortTaskHasFPUContext is zero then no.*/LDR     R0, ulPortTaskHasFPUContextConstPOP     {R1}STR     R1, [R0]CMP     R1, #0/* Restore the floating point context, if any. */VPOPNE  {D0-D15}POPNE   {R0}VMSRNE  FPSCR, R0#endif /* __ARM_FP *//* Restore the critical section nesting depth. */LDR     R0, ulCriticalNestingConstPOP     {R1}STR     R1, [R0]/* Ensure the priority mask is correct for the critical nesting depth. */LDR     R2, ulICCPMRConstLDR     R2, [R2]CMP     R1, #0MOVEQ   R4, #255LDRNE   R4, ulMaxAPIPriorityMaskConstLDRNE   R4, [R4]STR     R4, [R2]/* Restore all system mode registers other than the SP (which is alreadybeing used). */POP     {R0-R12, R14}/* Return to the task code, loading CPSR on the way. */RFEIA   sp!.endm

4.8 pxPortInitialiseStack

针对Cortex-R5处理器所设置的栈结构如下图所示：

StackType_t * pxPortInitialiseStack( StackType_t * pxTopOfStack,TaskFunction_t pxCode,void * pvParameters )
{/** Setup the initial stack of the task.  The stack is set exactly as* expected by the portRESTORE_CONTEXT() macro.** The fist real value on the stack is the status register, which is set for* system mode, with interrupts enabled.  A few NULLs are added first to ensure* GDB does not try decoding a non-existent return address.*/*pxTopOfStack = ( StackType_t ) NULL;pxTopOfStack--;*pxTopOfStack = ( StackType_t ) NULL;pxTopOfStack--;*pxTopOfStack = ( StackType_t ) NULL;pxTopOfStack--;*pxTopOfStack = ( StackType_t ) portINITIAL_SPSR;if( ( ( uint32_t ) pxCode & portTHUMB_MODE_ADDRESS ) != 0x00UL ){/* The task will start in THUMB mode. */*pxTopOfStack |= portTHUMB_MODE_BIT;}pxTopOfStack--;/* Next the return address, which in this case is the start of the task. */*pxTopOfStack = ( StackType_t ) pxCode;pxTopOfStack--;/* Next all the registers other than the stack pointer. */*pxTopOfStack = ( StackType_t ) portTASK_RETURN_ADDRESS; /* R14 */pxTopOfStack--;*pxTopOfStack = ( StackType_t ) 0x12121212;              /* R12 */pxTopOfStack--;*pxTopOfStack = ( StackType_t ) 0x11111111;              /* R11 */pxTopOfStack--;*pxTopOfStack = ( StackType_t ) 0x10101010;              /* R10 */pxTopOfStack--;*pxTopOfStack = ( StackType_t ) 0x09090909;              /* R9 */pxTopOfStack--;*pxTopOfStack = ( StackType_t ) 0x08080808;              /* R8 */pxTopOfStack--;*pxTopOfStack = ( StackType_t ) 0x07070707;              /* R7 */pxTopOfStack--;*pxTopOfStack = ( StackType_t ) 0x06060606;              /* R6 */pxTopOfStack--;*pxTopOfStack = ( StackType_t ) 0x05050505;              /* R5 */pxTopOfStack--;*pxTopOfStack = ( StackType_t ) 0x04040404;              /* R4 */pxTopOfStack--;*pxTopOfStack = ( StackType_t ) 0x03030303;              /* R3 */pxTopOfStack--;*pxTopOfStack = ( StackType_t ) 0x02020202;              /* R2 */pxTopOfStack--;*pxTopOfStack = ( StackType_t ) 0x01010101;              /* R1 */pxTopOfStack--;*pxTopOfStack = ( StackType_t ) pvParameters;            /* R0 *//** The task will start with a critical nesting count of 0 as interrupts are* enabled.*/pxTopOfStack--;*pxTopOfStack = portNO_CRITICAL_NESTING;#if ( configUSE_TASK_FPU_SUPPORT == 1 ){/** The task will start without a floating point context.* A task that uses the floating point hardware must call* vPortTaskUsesFPU() before executing any floating point* instructions.*/pxTopOfStack--;*pxTopOfStack = portNO_FLOATING_POINT_CONTEXT;}#elif ( configUSE_TASK_FPU_SUPPORT == 2 ){/** The task will start with a floating point context. Leave enough* space for the registers and ensure they are initialized to 0.*/pxTopOfStack -= portFPU_REGISTER_WORDS;memset( pxTopOfStack, 0x00, portFPU_REGISTER_WORDS * sizeof( StackType_t ) );pxTopOfStack--;*pxTopOfStack = pdTRUE;ulPortTaskHasFPUContext = pdTRUE;}#elif ( configUSE_TASK_FPU_SUPPORT != 0 ){#error Invalid configUSE_TASK_FPU_SUPPORT setting - configUSE_TASK_FPU_SUPPORT must be set to 0, 1, or 2.}#endif /* configUSE_TASK_FPU_SUPPORT */return pxTopOfStack;
}