Event Group 분석 — Bit Flag·AND/OR Wait·Sync Barrier

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typedef struct EventGroupDef_t {
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    EventBits_t uxEventBits;          // 24-bit flag (8 bits = control)
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    List_t xTasksWaitingForBits;      // 대기 task list
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    UBaseType_t uxEventGroupNumber;   // debug
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    uint8_t ucStaticallyAllocated;
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} EventGroup_t;
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typedef uint32_t EventBits_t;
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#define eventEVENT_BITS_CONTROL_BYTES  0xff000000UL   // 상위 8-bit 예약

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EventBits_t xEventGroupSetBits(EventGroupHandle_t xEventGroup,
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                                const EventBits_t uxBitsToSet) {
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    EventBits_t uxBitsToClear = 0;
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    BaseType_t xMatchFound = pdFALSE;
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    vTaskSuspendAll();
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    {
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        ListItem_t *pxListItem = listGET_HEAD_ENTRY(&xEventGroup->xTasksWaitingForBits);
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        eventGroup->uxEventBits |= uxBitsToSet;
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        /* 대기 task 순회 — 조건 만족 시 wake */
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        while (pxListItem != listGET_END_MARKER(&xEventGroup->xTasksWaitingForBits)) {
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            EventBits_t uxBitsWaitedFor = listGET_LIST_ITEM_VALUE(pxListItem);
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            EventBits_t uxControlBits = uxBitsWaitedFor & eventEVENT_BITS_CONTROL_BYTES;
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            uxBitsWaitedFor &= ~eventEVENT_BITS_CONTROL_BYTES;
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            if ((uxControlBits & eventWAIT_FOR_ALL_BITS) == 0) {
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                /* OR — 하나라도 match */
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                if ((uxBitsWaitedFor & xEventGroup->uxEventBits) != 0) {
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                    xMatchFound = pdTRUE;
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                }
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            } else {
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                /* AND — 모두 match */
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                if ((uxBitsWaitedFor & xEventGroup->uxEventBits) == uxBitsWaitedFor) {
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                    xMatchFound = pdTRUE;
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                }
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            }
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            if (xMatchFound) {
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                if (uxControlBits & eventCLEAR_EVENTS_ON_EXIT_BIT) {
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                    uxBitsToClear |= uxBitsWaitedFor;
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                }
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                vTaskRemoveFromUnorderedEventList(pxListItem,
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                    xEventGroup->uxEventBits | eventUNBLOCKED_DUE_TO_BIT_SET);
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            }
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            pxListItem = pxNext;
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            xMatchFound = pdFALSE;
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        }
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        /* Clear-on-exit 누적 적용 */
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        xEventGroup->uxEventBits &= ~uxBitsToClear;
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    }
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    xTaskResumeAll();
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    return xEventGroup->uxEventBits;
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}

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EventBits_t xEventGroupWaitBits(EventGroupHandle_t xEventGroup,
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                                 const EventBits_t uxBitsToWaitFor,
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                                 const BaseType_t xClearOnExit,
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                                 const BaseType_t xWaitForAllBits,
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                                 TickType_t xTicksToWait) {
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    EventBits_t uxReturn;
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    vTaskSuspendAll();
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    {
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        EventBits_t uxCurrentEventBits = xEventGroup->uxEventBits;
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        /* 즉시 만족하는가? */
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        if (xWaitForAllBits == pdFALSE) {
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            /* OR */
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            if ((uxCurrentEventBits & uxBitsToWaitFor) != 0) {
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                uxReturn = uxCurrentEventBits;
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                if (xClearOnExit) {
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                    xEventGroup->uxEventBits &= ~uxBitsToWaitFor;
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                }
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                xTaskResumeAll();
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                return uxReturn;
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            }
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        } else {
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            /* AND */
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            if ((uxCurrentEventBits & uxBitsToWaitFor) == uxBitsToWaitFor) {
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                uxReturn = uxCurrentEventBits;
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                if (xClearOnExit) {
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                    xEventGroup->uxEventBits &= ~uxBitsToWaitFor;
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                }
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                xTaskResumeAll();
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                return uxReturn;
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            }
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        }
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        /* 만족하지 않음 — block */
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        if (xTicksToWait != 0) {
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            EventBits_t uxControlBits = 0;
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            if (xClearOnExit) uxControlBits |= eventCLEAR_EVENTS_ON_EXIT_BIT;
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            if (xWaitForAllBits) uxControlBits |= eventWAIT_FOR_ALL_BITS;
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            vTaskPlaceOnUnorderedEventList(&xEventGroup->xTasksWaitingForBits,
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                uxBitsToWaitFor | uxControlBits, xTicksToWait);
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        }
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    }
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    xTaskResumeAll();
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    portYIELD_WITHIN_API();
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    /* Wake 후 — list item value에 결과가 인코딩돼 있음 */
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    uxReturn = uxTaskResetEventItemValue();
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    return uxReturn & ~eventEVENT_BITS_CONTROL_BYTES;
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}

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EventBits_t xEventGroupSync(EventGroupHandle_t xEventGroup,
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                             const EventBits_t uxBitsToSet,
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                             const EventBits_t uxBitsToWaitFor,
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                             TickType_t xTicksToWait);
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/* 사용 예 — 3 task barrier */
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#define TASK_A_DONE  (1 << 0)
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#define TASK_B_DONE  (1 << 1)
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#define TASK_C_DONE  (1 << 2)
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#define ALL_DONE     (TASK_A_DONE | TASK_B_DONE | TASK_C_DONE)
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void task_a(void *p) {
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    /* ... work ... */
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    xEventGroupSync(eg, TASK_A_DONE, ALL_DONE, portMAX_DELAY);
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    /* 셋 다 도착해야 여기에 도달 */
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}

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BaseType_t xEventGroupSetBitsFromISR(EventGroupHandle_t eg,
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                                      EventBits_t bits,
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                                      BaseType_t *pxHigherPriorityTaskWoken);

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ISR → xTimerPendFunctionCallFromISR(set_bits_fn, eg, bits)
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        → Daemon task가 깨어나 실제 SetBits 호출

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#define BIT_CONNECTED   (1 << 0)
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#define BIT_GOT_IP      (1 << 1)
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#define BIT_DNS_READY   (1 << 2)
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#define BIT_ALL_READY   (BIT_CONNECTED | BIT_GOT_IP | BIT_DNS_READY)
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void wifi_event_handler(wifi_event_t e) {
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    if (e == WIFI_CONNECTED)
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        xEventGroupSetBits(net_eg, BIT_CONNECTED);
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    if (e == WIFI_GOT_IP)
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        xEventGroupSetBits(net_eg, BIT_GOT_IP);
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    if (e == WIFI_DNS_READY)
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        xEventGroupSetBits(net_eg, BIT_DNS_READY);
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}
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void app_task(void *p) {
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    /* 세 조건이 모두 만족될 때까지 대기 */
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    xEventGroupWaitBits(net_eg, BIT_ALL_READY,
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        pdFALSE, pdTRUE /* AND */, portMAX_DELAY);
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    start_mqtt_client();
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}

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SetBits:
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- vTaskSuspendAll: 5 cycle
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- iterate wait list: 30 cycle × N waiters
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- match check: 10 cycle × N
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- portYIELD_WITHIN_API: 50 cycle
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Total ≈ 60 + N × 40 cycle
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WaitBits (즉시 만족): 30 cycle
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WaitBits (block + wake): ~200 cycle

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bits = xEventGroupGetBits(eg);
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if (bits & BIT_X) {
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    /* 여기서 다른 task가 clear할 수 있음 */
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    do_stuff();
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}