freeRtos原始碼決議(一)–任務創建與任務調度
一、簡介
??1.1 代碼來源及版本
??代碼來源于STM32CubeIDE工具一鍵生成功能，對應freeRtos版本為 FreeRTOS Kernel V10.2.1，對應MCU型號為STM32MP157D cortex-M4，
?? 生成的中間層代碼以及原始碼目錄如下：
??1.2 學習參考
??[野火?]《FreeRTOS 內核實作與應用開發實戰—基于STM32》、
?《FreeRTOS高級篇》https://blog.csdn.net/zhzht19861011/article/details/51418383
??freeRtos學習的人非常廣泛，資料眾多，每個版本間有細微的差別，可以相互參考，
二、任務與freeRtos
??freeRtos的核心，一句話就是：在裸機系統上實作多任務的實時調度以及提供任務間的通信同步機制， 歸結為一個詞，就是多任務 （任務創建，任務調度，任務通信），
??有些人把任務理解為linux中的執行緒，不過在freeRtos中沒有行程執行緒的概念，統一的叫法是任務task而不是thread，行程、執行緒的概念要到了linux內核中才存在，
三、任務創建
?? 3.1 xTaskCreate 任務創建介面
??任務創建對應的程序非常重要，需要仔細閱讀，介面代碼如下：
#if( configSUPPORT_DYNAMIC_ALLOCATION == 1 )
BaseType_t xTaskCreate( TaskFunction_t pxTaskCode,
const char * const pcName, /*lint !e971 Unqualified char types are allowed for strings and single characters only. */
const configSTACK_DEPTH_TYPE usStackDepth,
void * const pvParameters,
UBaseType_t uxPriority,
TaskHandle_t * const pxCreatedTask )
{
TCB_t *pxNewTCB;
BaseType_t xReturn;
/* If the stack grows down then allocate the stack then the TCB so the stack
does not grow into the TCB. Likewise if the stack grows up then allocate
the TCB then the stack. */
#if( portSTACK_GROWTH > 0 )
{
/* Allocate space for the TCB. Where the memory comes from depends on
the implementation of the port malloc function and whether or not static
allocation is being used. */
pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) );
if( pxNewTCB != NULL )
{
/* Allocate space for the stack used by the task being created.
The base of the stack memory stored in the TCB so the task can
be deleted later if required. */
pxNewTCB->pxStack = ( StackType_t * ) pvPortMalloc( ( ( ( size_t ) usStackDepth ) * sizeof( StackType_t ) ) ); /*lint !e961 MISRA exception as the casts are only redundant for some ports. */
if( pxNewTCB->pxStack == NULL )
{
/* Could not allocate the stack. Delete the allocated TCB. */
vPortFree( pxNewTCB );
pxNewTCB = NULL;
}
}
}
#else /* portSTACK_GROWTH */
{
StackType_t *pxStack;
/* Allocate space for the stack used by the task being created. */
pxStack = pvPortMalloc( ( ( ( size_t ) usStackDepth ) * sizeof( StackType_t ) ) ); /*lint !e9079 All values returned by pvPortMalloc() have at least the alignment required by the MCU's stack and this allocation is the stack. */
if( pxStack != NULL )
{
/* Allocate space for the TCB. */
pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) ); /*lint !e9087 !e9079 All values returned by pvPortMalloc() have at least the alignment required by the MCU's stack, and the first member of TCB_t is always a pointer to the task's stack. */
if( pxNewTCB != NULL )
{
/* Store the stack location in the TCB. */
pxNewTCB->pxStack = pxStack;
}
else
{
/* The stack cannot be used as the TCB was not created. Free
it again. */
vPortFree( pxStack );
}
}
else
{
pxNewTCB = NULL;
}
}
#endif /* portSTACK_GROWTH */
if( pxNewTCB != NULL )
{
#if( tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE != 0 ) /*lint !e9029 !e731 Macro has been consolidated for readability reasons. */
{
/* Tasks can be created statically or dynamically, so note this
task was created dynamically in case it is later deleted. */
pxNewTCB->ucStaticallyAllocated = tskDYNAMICALLY_ALLOCATED_STACK_AND_TCB;
}
#endif /* tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE */
prvInitialiseNewTask( pxTaskCode, pcName, ( uint32_t ) usStackDepth, pvParameters, uxPriority, pxCreatedTask, pxNewTCB, NULL );
prvAddNewTaskToReadyList( pxNewTCB );
xReturn = pdPASS;
}
else
{
xReturn = errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY;
}
return xReturn;
}
#endif /* configSUPPORT_DYNAMIC_ALLOCATION */
??相關宏定義：
#define configSUPPORT_DYNAMIC_ALLOCATION 1 // 表示支持動態分配TCB塊的空間和TCB對應堆疊的空間
#define portSTACK_GROWTH ( -1 ) // 表示堆疊地址是從低到高增長的
tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE // 未定義
??因此從函式38行開始，申請堆疊大小*4位元組的堆空間，作為任務堆疊的大小，
pxStack = pvPortMalloc( ( ( ( size_t ) usStackDepth ) * sizeof( StackType_t ) ) );
??申請TCB任務控制塊的空間，并且為其成員pxStack 賦值，作為任務堆疊的起始地址，
pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) );
pxNewTCB->pxStack = pxStack;
?? 3.2 prvInitialiseNewTask 初始化TCB任務控制塊
??初始化TCB任務控制塊的成員，代碼如下：
static void prvInitialiseNewTask( TaskFunction_t pxTaskCode,
const char * const pcName, /*lint !e971 Unqualified char types are allowed for strings and single characters only. */
const uint32_t ulStackDepth,
void * const pvParameters,
UBaseType_t uxPriority,
TaskHandle_t * const pxCreatedTask,
TCB_t *pxNewTCB,
const MemoryRegion_t * const xRegions )
{
StackType_t *pxTopOfStack;
UBaseType_t x;
#if( portUSING_MPU_WRAPPERS == 1 )
/* Should the task be created in privileged mode? */
BaseType_t xRunPrivileged;
if( ( uxPriority & portPRIVILEGE_BIT ) != 0U )
{
xRunPrivileged = pdTRUE;
}
else
{
xRunPrivileged = pdFALSE;
}
uxPriority &= ~portPRIVILEGE_BIT;
#endif /* portUSING_MPU_WRAPPERS == 1 */
/* Avoid dependency on memset() if it is not required. */
#if( tskSET_NEW_STACKS_TO_KNOWN_VALUE == 1 )
{
/* Fill the stack with a known value to assist debugging. */
( void ) memset( pxNewTCB->pxStack, ( int ) tskSTACK_FILL_BYTE, ( size_t ) ulStackDepth * sizeof( StackType_t ) );
}
#endif /* tskSET_NEW_STACKS_TO_KNOWN_VALUE */
/* Calculate the top of stack address. This depends on whether the stack
grows from high memory to low (as per the 80x86) or vice versa.
portSTACK_GROWTH is used to make the result positive or negative as required
by the port. */
#if( portSTACK_GROWTH < 0 )
{
pxTopOfStack = &( pxNewTCB->pxStack[ ulStackDepth - ( uint32_t ) 1 ] );
pxTopOfStack = ( StackType_t * ) ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack ) & ( ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) ) ); /*lint !e923 !e9033 !e9078 MISRA exception. Avoiding casts between pointers and integers is not practical. Size differences accounted for using portPOINTER_SIZE_TYPE type. Checked by assert(). */
/* Check the alignment of the calculated top of stack is correct. */
configASSERT( ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack & ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) == 0UL ) );
#if( configRECORD_STACK_HIGH_ADDRESS == 1 )
{
/* Also record the stack's high address, which may assist
debugging. */
pxNewTCB->pxEndOfStack = pxTopOfStack;
}
#endif /* configRECORD_STACK_HIGH_ADDRESS */
}
#else /* portSTACK_GROWTH */
{
pxTopOfStack = pxNewTCB->pxStack;
/* Check the alignment of the stack buffer is correct. */
configASSERT( ( ( ( portPOINTER_SIZE_TYPE ) pxNewTCB->pxStack & ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) == 0UL ) );
/* The other extreme of the stack space is required if stack checking is
performed. */
pxNewTCB->pxEndOfStack = pxNewTCB->pxStack + ( ulStackDepth - ( uint32_t ) 1 );
}
#endif /* portSTACK_GROWTH */
/* Store the task name in the TCB. */
if( pcName != NULL )
{
for( x = ( UBaseType_t ) 0; x < ( UBaseType_t ) configMAX_TASK_NAME_LEN; x++ )
{
pxNewTCB->pcTaskName[ x ] = pcName[ x ];
/* 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( pcName[ x ] == ( char ) 0x00 )
{
break;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
/* Ensure the name string is terminated in the case that the string length
was greater or equal to configMAX_TASK_NAME_LEN. */
pxNewTCB->pcTaskName[ configMAX_TASK_NAME_LEN - 1 ] = '\0';
}
else
{
/* The task has not been given a name, so just ensure there is a NULL
terminator when it is read out. */
pxNewTCB->pcTaskName[ 0 ] = 0x00;
}
/* This is used as an array index so must ensure it's not too large. First
remove the privilege bit if one is present. */
if( uxPriority >= ( UBaseType_t ) configMAX_PRIORITIES )
{
uxPriority = ( UBaseType_t ) configMAX_PRIORITIES - ( UBaseType_t ) 1U;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
pxNewTCB->uxPriority = uxPriority;
#if ( configUSE_MUTEXES == 1 )
{
pxNewTCB->uxBasePriority = uxPriority;
pxNewTCB->uxMutexesHeld = 0;
}
#endif /* configUSE_MUTEXES */
vListInitialiseItem( &( pxNewTCB->xStateListItem ) );
vListInitialiseItem( &( pxNewTCB->xEventListItem ) );
/* Set the pxNewTCB as a link back from the ListItem_t. This is so we can get
back to the containing TCB from a generic item in a list. */
listSET_LIST_ITEM_OWNER( &( pxNewTCB->xStateListItem ), pxNewTCB );
/* Event lists are always in priority order. */
listSET_LIST_ITEM_VALUE( &( pxNewTCB->xEventListItem ), ( TickType_t ) configMAX_PRIORITIES - ( TickType_t ) uxPriority ); /*lint !e961 MISRA exception as the casts are only redundant for some ports. */
listSET_LIST_ITEM_OWNER( &( pxNewTCB->xEventListItem ), pxNewTCB );
#if ( portCRITICAL_NESTING_IN_TCB == 1 )
{
pxNewTCB->uxCriticalNesting = ( UBaseType_t ) 0U;
}
#endif /* portCRITICAL_NESTING_IN_TCB */
#if ( configUSE_APPLICATION_TASK_TAG == 1 )
{
pxNewTCB->pxTaskTag = NULL;
}
#endif /* configUSE_APPLICATION_TASK_TAG */
#if ( configGENERATE_RUN_TIME_STATS == 1 )
{
pxNewTCB->ulRunTimeCounter = 0UL;
}
#endif /* configGENERATE_RUN_TIME_STATS */
#if ( portUSING_MPU_WRAPPERS == 1 )
{
vPortStoreTaskMPUSettings( &( pxNewTCB->xMPUSettings ), xRegions, pxNewTCB->pxStack, ulStackDepth );
}
#else
{
/* Avoid compiler warning about unreferenced parameter. */
( void ) xRegions;
}
#endif
#if( configNUM_THREAD_LOCAL_STORAGE_POINTERS != 0 )
{
for( x = 0; x < ( UBaseType_t ) configNUM_THREAD_LOCAL_STORAGE_POINTERS; x++ )
{
pxNewTCB->pvThreadLocalStoragePointers[ x ] = NULL;
}
}
#endif
#if ( configUSE_TASK_NOTIFICATIONS == 1 )
{
pxNewTCB->ulNotifiedValue = 0;
pxNewTCB->ucNotifyState = taskNOT_WAITING_NOTIFICATION;
}
#endif
#if ( configUSE_NEWLIB_REENTRANT == 1 )
{
/* Initialise this task's Newlib reent structure. */
_REENT_INIT_PTR( ( &( pxNewTCB->xNewLib_reent ) ) );
}
#endif
#if( INCLUDE_xTaskAbortDelay == 1 )
{
pxNewTCB->ucDelayAborted = pdFALSE;
}
#endif
/* Initialize the TCB stack to look as if the task was already running,
but had been interrupted by the scheduler. The return address is set
to the start of the task function. Once the stack has been initialised
the top of stack variable is updated. */
#if( portUSING_MPU_WRAPPERS == 1 )
{
/* If the port has capability to detect stack overflow,
pass the stack end address to the stack initialization
function as well. */
#if( portHAS_STACK_OVERFLOW_CHECKING == 1 )
{
#if( portSTACK_GROWTH < 0 )
{
pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxNewTCB->pxStack, pxTaskCode, pvParameters, xRunPrivileged );
}
#else /* portSTACK_GROWTH */
{
pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxNewTCB->pxEndOfStack, pxTaskCode, pvParameters, xRunPrivileged );
}
#endif /* portSTACK_GROWTH */
}
#else /* portHAS_STACK_OVERFLOW_CHECKING */
{
pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters, xRunPrivileged );
}
#endif /* portHAS_STACK_OVERFLOW_CHECKING */
}
#else /* portUSING_MPU_WRAPPERS */
{
/* If the port has capability to detect stack overflow,
pass the stack end address to the stack initialization
function as well. */
#if( portHAS_STACK_OVERFLOW_CHECKING == 1 )
{
#if( portSTACK_GROWTH < 0 )
{
pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxNewTCB->pxStack, pxTaskCode, pvParameters );
}
#else /* portSTACK_GROWTH */
{
pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxNewTCB->pxEndOfStack, pxTaskCode, pvParameters );
}
#endif /* portSTACK_GROWTH */
}
#else /* portHAS_STACK_OVERFLOW_CHECKING */
{
pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters );
}
#endif /* portHAS_STACK_OVERFLOW_CHECKING */
}
#endif /* portUSING_MPU_WRAPPERS */
if( pxCreatedTask != NULL )
{
/* Pass the handle out in an anonymous way. The handle can be used to
change the created task's priority, delete the created task, etc.*/
*pxCreatedTask = ( TaskHandle_t ) pxNewTCB;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
?? 3.3 pxPortInitialiseStack 初始化任務堆疊指標（根據MCU內核通用暫存器偏移）
?? 3.4 prvAddNewTaskToReadyList 將TCB控制塊加入到ready串列中
??至此，完成了任務的創建和初始化，
四、啟動任務調度器
??啟動任務調度器之后，CPU正式開始按照任務的方式調度各任務，
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