FreeRTOS?????SysTick???

1. FreeRTOS????

1.1 ??????

FreeRTOS??????????????

static List_t xDelayedTaskList1;

static List_t xDelayedTaskList2;

static List_t * volatile pxDelayedTaskList;

static List_t * volatile pxOverflowDelayedTaskList;

static volatile TickType_t xNextTaskUnblockTime

???????????????????????????????????????xTickCount?uint32_t???????????FreeRTOS?????????????????????????????

?xTickCount?????????pxDelayedTaskList?pxOverflowDelayedTaskList????xNextTaskUnblockTime??????????????????????????

1.2 vTaskDelay??

vTaskDelay????????????????????????????????????????????????????????????????????????

1.2.1 ????

void vTaskDelay(const TickType_t xTicksToDelay) {    BaseType_t xAlreadyYielded = pdFALSE;    if (xTicksToDelay > (TickType_t)0U) {        configASSERT(uxSchedulerSuspended == 0);        vTaskSuspendAll();        prvAddCurrentTaskToDelayedList(xTicksToDelay, pdFALSE);        xAlreadyYielded = xTaskResumeAll();    }    if (xAlreadyYielded == pdFALSE) {        portYIELD_WITHIN_API();    }}

1.2.2 ??

???????????????????

???????vTaskDelay????????????????????

??????????????????????
- ?10ms????
- ???????10ms

1.3 vTaskDelayUntil??

vTaskDelayUntil??????????????????????????????????????xTimeIncrement??????????????????

1.3.1 ????

void vTaskDelayUntil(TickType_t * const pxPreviousWakeTime, const TickType_t xTimeIncrement) {    TickType_t xTimeToWake;    BaseType_t xAlreadyYielded, xShouldDelay = pdFALSE;    configASSERT(pxPreviousWakeTime);    configASSERT(xTimeIncrement > 0U);    configASSERT(uxSchedulerSuspended == 0);    vTaskSuspendAll();    {        const TickType_t xConstTickCount = xTickCount;        xTimeToWake = *pxPreviousWakeTime + xTimeIncrement;        if (xConstTickCount < *pxPreviousWakeTime) {            if ((xTimeToWake < *pxPreviousWakeTime) && (xTimeToWake > xConstTickCount)) {                xShouldDelay = pdTRUE;            }        } else {            if ((xTimeToWake < *pxPreviousWakeTime) || (xTimeToWake > xConstTickCount)) {                xShouldDelay = pdTRUE;            }        }        *pxPreviousWakeTime = xTimeToWake;        if (xShouldDelay != pdFALSE) {            prvAddCurrentTaskToDelayedList(xTimeToWake - xConstTickCount, pdFALSE);        }    }    xAlreadyYielded = xTaskResumeAll();    if (xAlreadyYielded == pdFALSE) {        portYIELD_WITHIN_API();    }}

1.3.2 ??

?????????????????????????

?????????xTimeIncrement????????????????????????????????????

????????????????????????????????

xConstTickCount?xTimeToWake????

xConstTickCount????xTimeToWake??

xConstTickCount?xTimeToWake???

2. FreeRTOS????

2.1 SysTick???

SysTick??Cortex-M?????????24??????????????FreeRTOS??SysTick??????????????????????

2.1.2 ?????

SysTick?4????????

CTRL???????????????

LOAD???????????????

2.1.3 ????

vPortSetupTimerInterrupt();

2.1.3 ??

?????SysTick??????configTICK_RATE_HZ?configSYSTICK_CLOCK_HZ?????

??????????????????????????

2.2 SysTick????

2.2.1 xPortSysTickHandler??

SysTick????????????xTaskIncrementTick????????????????????

2.2.2 xTaskIncrementTick??

BaseType_t xTaskIncrementTick(void) {    if (uxSchedulerSuspended == pdFALSE) {        xTickCount++;        if (xTickCount == (TickType_t)0U) {            taskSWITCH_DELAYED_LISTS();        }        if (xTickCount >= xNextTaskUnblockTime) {            while (listLIST_IS_EMPTY(pxDelayedTaskList) == pdFALSE) {                pxTCB = listGET_OWNER_OF_HEAD_ENTRY(pxDelayedTaskList);                xItemValue = listGET_LIST_ITEM_VALUE(pxTCB->xStateListItem);                if (xTickCount < xItemValue) {                    xNextTaskUnblockTime = xItemValue;                    break;                }                uxListRemove(pxTCB->xStateListItem);                if (listLIST_ITEM_CONTAINER(pxTCB->xEventListItem) != NULL) {                    uxListRemove(pxTCB->xEventListItem);                }                prvAddTaskToReadyList(pxTCB);                #if (configUSE_PREEMPTION == 1)                    if (pxTCB->uxPriority >= pxCurrentTCB->uxPriority) {                        xSwitchRequired = pdTRUE;                    }                #endif            }            xNextTaskUnblockTime = portMAX_DELAY;        }        #if (configUSE_PREEMPTION == 1 && configUSE_TIME_SLICING == 1)            if (listCURRENT_LIST_LENGTH(pxReadyTasksLists[pxCurrentTCB->uxPriority]) > 1) {                xSwitchRequired = pdTRUE;            }        #endif    } else {        uxPendedTicks++;    }    #if (configUSE_PREEMPTION == 1)        if (xYieldPending != pdFALSE) {            xSwitchRequired = pdTRUE;        }    #endif    return xSwitchRequired;}