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;
}