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任务创建xTaskCreate
/**
* task. h
*<pre>
portBASE_TYPE xTaskCreate(
pdTASK_CODE pvTaskCode,
const char * const pcName,
unsigned short usStackDepth,
void *pvParameters,
unsigned portBASE_TYPE uxPriority,
xTaskHandle *pvCreatedTask
);</pre>
*
* Create a new task and add it to the list of tasks that are ready to run.
*
* xTaskCreate() can only be used to create a task that has unrestricted
* access to the entire microcontroller memory map. Systems that include MPU
* support can alternatively create an MPU constrained task using
* xTaskCreateRestricted().
*
* @param pvTaskCode Pointer to the task entry function. Tasks
* must be implemented to never return (i.e. continuous loop).
*
* @param pcName A descriptive name for the task. This is mainly used to
* facilitate debugging. Max length defined by tskMAX_TASK_NAME_LEN - default
* is 16.
*
* @param usStackDepth The size of the task stack specified as the number of
* variables the stack can hold - not the number of bytes. For example, if
* the stack is 16 bits wide and usStackDepth is defined as 100, 200 bytes
* will be allocated for stack storage.
*
* @param pvParameters Pointer that will be used as the parameter for the task
* being created.
*
* @param uxPriority The priority at which the task should run. Systems that
* include MPU support can optionally create tasks in a privileged (system)
* mode by setting bit portPRIVILEGE_BIT of the priority parameter. For
* example, to create a privileged task at priority 2 the uxPriority parameter
* should be set to ( 2 | portPRIVILEGE_BIT ).
*
* @param pvCreatedTask Used to pass back a handle by which the created task
* can be referenced.
*
* @return pdPASS if the task was successfully created and added to a ready
* list, otherwise an error code defined in the file errors. h
*
* Example usage:
<pre>
// Task to be created.
void vTaskCode( void * pvParameters )
{
for( ;; )
{
// Task code goes here.
}
}
// Function that creates a task.
void vOtherFunction( void )
{
static unsigned char ucParameterToPass;
xTaskHandle xHandle;
// Create the task, storing the handle. Note that the passed parameter ucParameterToPass
// must exist for the lifetime of the task, so in this case is declared static. If it was just an
// an automatic stack variable it might no longer exist, or at least have been corrupted, by the time
// the new task attempts to access it.
xTaskCreate( vTaskCode, "NAME", STACK_SIZE, &ucParameterToPass, tskIDLE_PRIORITY, &xHandle );
// Use the handle to delete the task.
vTaskDelete( xHandle );
}
signed portBASE_TYPE xTaskGenericCreate( pdTASK_CODE pxTaskCode,
const signed char * const pcName,
unsigned short usStackDepth,
void *pvParameters,
unsigned portBASE_TYPE uxPriority,
xTaskHandle *pxCreatedTask,
portSTACK_TYPE *puxStackBuffer,
const xMemoryRegion * const xRegions )
{
signed portBASE_TYPE xReturn;
tskTCB * pxNewTCB;
configASSERT( pxTaskCode );
configASSERT( ( ( uxPriority & ( ~portPRIVILEGE_BIT ) ) < configMAX_PRIORITIES ) );
/* Allocate the memory required by the TCB and stack for the new task,
checking that the allocation was successful. */
// 为任务分配TCB和堆栈空间
pxNewTCB = prvAllocateTCBAndStack( usStackDepth, puxStackBuffer );
if( pxNewTCB != NULL )
{
portSTACK_TYPE *pxTopOfStack;
#if( portUSING_MPU_WRAPPERS == 1 )
/* Should the task be created in privileged mode? */
//是否将任务设置成特权级模式
portBASE_TYPE xRunPrivileged;
if( ( uxPriority & portPRIVILEGE_BIT ) != 0U )
{
xRun00000Privileged = pdTRUE;
}
else
{
xRunPrivileged = pdFALSE;
}
uxPriority &= ~portPRIVILEGE_BIT;
#endif /* portUSING_MPU_WRAPPERS == 1 */
/* Calculate the top of stack address. This depends on whether the
stack grows from high memory to low (as per the 80x86) or visa versa.
portSTACK_GROWTH is used to make the result positive or negative as
required by the port. */
//堆栈的生长方向，从高地址到低地址
#if( portSTACK_GROWTH < 0 )
{
//初始化堆栈栈顶位置和堆栈的字节对其方式
pxTopOfStack = pxNewTCB->pxStack + ( usStackDepth - ( unsigned short ) 1 );
pxTopOfStack = ( portSTACK_TYPE * ) ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack ) & ( ( portPOINTER_SIZE_TYPE ) ~portBYTE_ALIGNMENT_MASK ) );
/* Check the alignment of the calculated top of stack is correct. */
configASSERT( ( ( ( unsigned long ) pxTopOfStack & ( unsigned long ) portBYTE_ALIGNMENT_MASK ) == 0UL ) );
}
//堆栈的生长方向，从低地址到高地址
#else /* portSTACK_GROWTH */
{
pxTopOfStack = pxNewTCB->pxStack;
/* Check the alignment of the stack buffer is correct. */
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. */
pxNewTCB->pxEndOfStack = pxNewTCB->pxStack + ( usStackDepth - 1 );
}
#endif /* portSTACK_GROWTH */
/* Setup the newly allocated TCB with the initial state of the task. */
//初始化任务控制块变量
prvInitialiseTCBVariables( pxNewTCB, pcName, uxPriority, xRegions, usStackDepth );
/* 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 )
{
pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters, xRunPrivileged );
}
#else /* portUSING_MPU_WRAPPERS */
{
pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters );
}
#endif /* portUSING_MPU_WRAPPERS */
/* Check the alignment of the initialised stack. */
portALIGNMENT_ASSERT_pxCurrentTCB( ( ( ( unsigned long ) pxNewTCB->pxTopOfStack & ( unsigned long ) portBYTE_ALIGNMENT_MASK ) == 0UL ) );
//返回任务的句柄
if( ( void * ) pxCreatedTask != NULL )
{
/* Pass the TCB out - in an anonymous way. The calling function/
task can use this as a handle to delete the task later if
required.*/
*pxCreatedTask = ( xTaskHandle ) pxNewTCB;
}
/* We are going to manipulate the task queues to add this task to a
ready list, so must make sure no interrupts occur. */
//
taskENTER_CRITICAL();
{
uxCurrentNumberOfTasks++;
if( pxCurrentTCB == NULL )
{
/* There are no other tasks, or all the other tasks are in
the suspended state - make this the current task. */
//当前没有任务执行
pxCurrentTCB = pxNewTCB;
//如果是第一个任务
if( uxCurrentNumberOfTasks == ( unsigned portBASE_TYPE ) 1 )
{
/* This is the first task to be created so do the preliminary
initialisation required. We will not recover if this call
fails, but we will report the failure. */
//初始化任务列表
prvInitialiseTaskLists();
}
}
else
{
/* If the scheduler is not already running, make this task the
current task if it is the highest priority task to be created
so far. */
if( xSchedulerRunning == pdFALSE )
{
if( pxCurrentTCB->uxPriority <= uxPriority )
{
pxCurrentTCB = pxNewTCB;
}
}
}
/* Remember the top priority to make context switching faster. Use
the priority in pxNewTCB as this has been capped to a valid value. */
if( pxNewTCB->uxPriority > uxTopUsedPriority )
{
uxTopUsedPriority = pxNewTCB->uxPriority;
}
uxTaskNumber++;
#if ( configUSE_TRACE_FACILITY == 1 )
{
/* Add a counter into the TCB for tracing only. */
pxNewTCB->uxTCBNumber = uxTaskNumber;
}
#endif /* configUSE_TRACE_FACILITY */
traceTASK_CREATE( pxNewTCB );
//将任务加入到就绪队列里面
prvAddTaskToReadyQueue( pxNewTCB );
xReturn = pdPASS;
portSETUP_TCB( pxNewTCB );
}
taskEXIT_CRITICAL();
}
//任务创建失败
else
{
xReturn = errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY;
traceTASK_CREATE_FAILED();
}
//创建成功
if( xReturn == pdPASS )
{
//如果开始任务调度
if( xSchedulerRunning != pdFALSE )
{
/* If the created task is of a higher priority than the current task
then it should run now. */
//判断是否需要任务切换
if( pxCurrentTCB->uxPriority < uxPriority )
{
portYIELD_WITHIN_API();
}
}
}
return xReturn;
} |
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发表于 2013-6-19 13:53:01
楼主
发表于 2014-5-8 19:06:06
