主機環境:Windows
開發環境:MDK4.7.2
FreeRTOS版本:FreeRTOS8.1.2
目標環境:STM32F030C8T6
FreeRTOS中關於時間的管理分爲兩部分：一部分是任務的延時管理;前面敘述過一些，還有一部分就是SysTick中斷，管理任務的延時時間。SysTick是由STM32內核提供的，時鐘源可選，用於產生FreeRTOS所需要的系統時鐘，且是由用戶可配的，用戶在FreeRTOSConfig.h文件中配置configCPU_CLOCK_HZ以及configTICK_RATE_HZ兩個宏來設置系統時鐘，產生時間片時間，系統每隔固定時間進入SysTick中斷處理時間。
有關時鐘配置的初始化函數在port.c文件中，如下
void prvSetupTimerInterrupt( void )
{
/* Configure SysTick to interrupt at the requested rate. */
*(portNVIC_SYSTICK_LOAD) = ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
*(portNVIC_SYSTICK_CTRL) = portNVIC_SYSTICK_CLK | portNVIC_SYSTICK_INT | portNVIC_SYSTICK_ENABLE;
}
LOAD寄存器是裝載的計數值由用戶配置，CTRL寄存器配置SYSTICK計數器的時鐘源以及是否產生中斷，且是否使能該計數器，該函數在調度器啓動時調用，即在xPortStartScheduler()函數中調用，啓動該計數器，這樣在計數值爲0時進入SysTick中斷函數，即xPortSysTickHandler()中斷函數
void xPortSysTickHandler( void )
{
uint32_t ulPreviousMask;
ulPreviousMask = portSET_INTERRUPT_MASK_FROM_ISR();
{
/* Increment the RTOS tick. */
if( xTaskIncrementTick() != pdFALSE )
{
/* Pend a context switch. */
*(portNVIC_INT_CTRL) = portNVIC_PENDSVSET;
}
}
portCLEAR_INTERRUPT_MASK_FROM_ISR( ulPreviousMask );
}
BaseType_t xTaskIncrementTick( void )
{
TCB_t * pxTCB;
TickType_t xItemValue;
BaseType_t xSwitchRequired = pdFALSE;
/* Called by the portable layer each time a tick interrupt occurs.
Increments the tick then checks to see if the new tick value will cause any
tasks to be unblocked. */
traceTASK_INCREMENT_TICK( xTickCount );
if( uxSchedulerSuspended == ( UBaseType_t ) pdFALSE )
{
/* Increment the RTOS tick, switching the delayed and overflowed
delayed lists if it wraps to 0. */
++xTickCount;
{
/* Minor optimisation. The tick count cannot change in this
block. */
const TickType_t xConstTickCount = xTickCount;
if( xConstTickCount == ( TickType_t ) 0U )
{
taskSWITCH_DELAYED_LISTS();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
/* See if this tick has made a timeout expire. Tasks are stored in
the queue in the order of their wake time - meaning once one task
has been found whose block time has not expired there is no need to
look any further down the list. */
if( xConstTickCount >= xNextTaskUnblockTime )
{
for( ;; )
{
if( listLIST_IS_EMPTY( pxDelayedTaskList ) != pdFALSE )
{
/* The delayed list is empty. Set xNextTaskUnblockTime
to the maximum possible value so it is extremely
unlikely that the
if( xTickCount >= xNextTaskUnblockTime ) test will pass
next time through. */
xNextTaskUnblockTime = portMAX_DELAY;
break;
}
else
{
/* The delayed list is not empty, get the value of the
item at the head of the delayed list. This is the time
at which the task at the head of the delayed list must
be removed from the Blocked state. */
pxTCB = ( TCB_t * ) listGET_OWNER_OF_HEAD_ENTRY( pxDelayedTaskList );
xItemValue = listGET_LIST_ITEM_VALUE( &( pxTCB->xGenericListItem ) );
if( xConstTickCount < xItemValue )
{
/* It is not time to unblock this item yet, but the
item value is the time at which the task at the head
of the blocked list must be removed from the Blocked
state - so record the item value in
xNextTaskUnblockTime. */
xNextTaskUnblockTime = xItemValue;
break;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
/* It is time to remove the item from the Blocked state. */
( void ) uxListRemove( &( pxTCB->xGenericListItem ) );
/* Is the task waiting on an event also? If so remove
it from the event list. */
if( listLIST_ITEM_CONTAINER( &( pxTCB->xEventListItem ) ) != NULL )
{
( void ) uxListRemove( &( pxTCB->xEventListItem ) );
}
else
{
mtCOVERAGE_TEST_MARKER();
}
/* Place the unblocked task into the appropriate ready
list. */
prvAddTaskToReadyList( pxTCB );
/* A task being unblocked cannot cause an immediate
context switch if preemption is turned off. */
#if ( configUSE_PREEMPTION == 1 )
{
/* Preemption is on, but a context switch should
only be performed if the unblocked task has a
priority that is equal to or higher than the
currently executing task. */
if( pxTCB->uxPriority >= pxCurrentTCB->uxPriority )
{
xSwitchRequired = pdTRUE;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
#endif /* configUSE_PREEMPTION */
}
}
}
}
/* Tasks of equal priority to the currently running task will share
processing time (time slice) if preemption is on, and the application
writer has not explicitly turned time slicing off. */
#if ( ( configUSE_PREEMPTION == 1 ) && ( configUSE_TIME_SLICING == 1 ) )
{
if( listCURRENT_LIST_LENGTH( &( pxReadyTasksLists[ pxCurrentTCB->uxPriority ] ) ) > ( UBaseType_t ) 1 )
{
xSwitchRequired = pdTRUE;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
#endif /* ( ( configUSE_PREEMPTION == 1 ) && ( configUSE_TIME_SLICING == 1 ) ) */
#if ( configUSE_TICK_HOOK == 1 )
{
/* Guard against the tick hook being called when the pended tick
count is being unwound (when the scheduler is being unlocked). */
if( uxPendedTicks == ( UBaseType_t ) 0U )
{
vApplicationTickHook();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
#endif /* configUSE_TICK_HOOK */
}
else
{
++uxPendedTicks;
/* The tick hook gets called at regular intervals, even if the
scheduler is locked. */
#if ( configUSE_TICK_HOOK == 1 )
{
vApplicationTickHook();
}
#endif
}
#if ( configUSE_PREEMPTION == 1 )
{
if( xYieldPending != pdFALSE )
{
xSwitchRequired = pdTRUE;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
#endif /* configUSE_PREEMPTION */
return xSwitchRequired;
}
#define taskSWITCH_DELAYED_LISTS() \
{ \
List_t *pxTemp; \
\
/* The delayed tasks list should be empty when the lists are switched. */ \
configASSERT( ( listLIST_IS_EMPTY( pxDelayedTaskList ) ) ); \
\
pxTemp = pxDelayedTaskList; \
pxDelayedTaskList = pxOverflowDelayedTaskList; \
pxOverflowDelayedTaskList = pxTemp; \
xNumOfOverflows++; \
prvResetNextTaskUnblockTime(); \
}
static void prvResetNextTaskUnblockTime( void )
{
TCB_t *pxTCB;
if( listLIST_IS_EMPTY( pxDelayedTaskList ) != pdFALSE )
{
/* The new current delayed list is empty. Set
xNextTaskUnblockTime to the maximum possible value so it is
extremely unlikely that the
if( xTickCount >= xNextTaskUnblockTime ) test will pass until
there is an item in the delayed list. */
xNextTaskUnblockTime = portMAX_DELAY;
}
else
{
/* The new current delayed list is not empty, get the value of
the item at the head of the delayed list. This is the time at
which the task at the head of the delayed list should be removed
from the Blocked state. */
( pxTCB ) = ( TCB_t * ) listGET_OWNER_OF_HEAD_ENTRY( pxDelayedTaskList );
xNextTaskUnblockTime = listGET_LIST_ITEM_VALUE( &( ( pxTCB )->xGenericListItem ) );
}
}
/* If any ticks occurred while the scheduler was suspended then
they should be processed now. This ensures the tick count does
not slip, and that any delayed tasks are resumed at the correct
time. */
if( uxPendedTicks > ( UBaseType_t ) 0U )
{
while( uxPendedTicks > ( UBaseType_t ) 0U )
{
if( xTaskIncrementTick() != pdFALSE )
{
xYieldPending = pdTRUE;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
--uxPendedTicks;
}
}
