Tickless 모드 구현 — Idle Tick Suppression·Sleep·Wake 보정

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@ 1 ms tick:
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Active during ISR (~3 µs): 10 mA × 3 µs = 30 nC/ms
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Sleep (~1 µA): 1 µA × 997 µs ≈ 1 nC/ms
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평균: ~31 µA  (1년 = 270 mAh)

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#define configUSE_TICKLESS_IDLE                 1
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#define configEXPECTED_IDLE_TIME_BEFORE_SLEEP   2
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void vPortSuppressTicksAndSleep(TickType_t xExpectedIdleTime) {
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    uint32_t ulReloadValue, ulCompletedSysTickDecrements;
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    TickType_t xModifiableIdleTime;
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    /* SysTick 멈춤 */
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    portNVIC_SYSTICK_CTRL_REG &= ~portNVIC_SYSTICK_ENABLE_BIT;
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    /* IRQ disable — atomic check */
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    __disable_irq();
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    __dsb(portSY_FULL_READ_WRITE);
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    __isb(portSY_FULL_READ_WRITE);
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    if (eTaskConfirmSleepModeStatus() == eAbortSleep) {
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        /* 마지막에 ready task 생김 — abort */
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        portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
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        __enable_irq();
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        return;
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    }
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    /* 다음 wake까지 SysTick reload */
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    ulReloadValue = portNVIC_SYSTICK_CURRENT_VALUE_REG +
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                    (ulTimerCountsForOneTick * (xExpectedIdleTime - 1UL));
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    portNVIC_SYSTICK_LOAD_REG = ulReloadValue;
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    portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
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    portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
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    /* Sleep — WFI */
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    xModifiableIdleTime = xExpectedIdleTime;
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    configPRE_SLEEP_PROCESSING(xModifiableIdleTime);
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    if (xModifiableIdleTime > 0) {
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        __dsb(portSY_FULL_READ_WRITE);
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        __wfi();
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        __isb(portSY_FULL_READ_WRITE);
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    }
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    configPOST_SLEEP_PROCESSING(xExpectedIdleTime);
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    /* SysTick 다시 default reload */
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    portNVIC_SYSTICK_CTRL_REG &= ~portNVIC_SYSTICK_ENABLE_BIT;
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    portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;
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    /* 실제 경과 tick 보충 */
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    if (/* SysTick interrupt가 trigger 됐다면 */) {
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        ulCompletedSysTickDecrements = (xExpectedIdleTime * ulTimerCountsForOneTick) -
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                                         portNVIC_SYSTICK_CURRENT_VALUE_REG;
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        ulCompleteTickPeriods = ulCompletedSysTickDecrements / ulTimerCountsForOneTick;
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    } else {
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        /* 다른 IRQ로 깨어남 */
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        ulCompleteTickPeriods = /* 계산 */;
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    }
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    vTaskStepTick(ulCompleteTickPeriods);
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    portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
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    portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
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    __enable_irq();
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}

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void configPRE_SLEEP_PROCESSING(TickType_t xExpectedIdleTime) {
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    /* Switch clocks to low power */
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    HAL_SuspendTick();
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    /* Stop mode 진입 */
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    HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI);
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}
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void configPOST_SLEEP_PROCESSING(TickType_t xExpectedIdleTime) {
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    /* Stop mode에서 깨어남 — clock 재설정 */
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    SystemClock_Config();   // PLL 등 재시작
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    HAL_ResumeTick();
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}

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// Main task — 매 분 wake
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void sensor_task(void *arg) {
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    while (1) {
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        read_sensor();
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        send_radio();
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        vTaskDelay(pdMS_TO_TICKS(60000));   // 1분 — tickless OK
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    }
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}

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// 다음 wake 시점을 RTC alarm으로
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RTC_AlarmTypeDef alarm;
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alarm.AlarmTime.Hours = ...;
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alarm.AlarmTime.Minutes = ...;
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HAL_RTC_SetAlarm_IT(&hrtc, &alarm, RTC_FORMAT_BIN);
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/* Standby 진입 */
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HAL_PWR_EnterSTANDBYMode();

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// devicetree
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power-states {
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    state0: state0 {
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        compatible = "zephyr,power-state";
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        power-state-name = "suspend-to-idle";
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        min-residency-us = <100>;
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    };
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    state1: state1 {
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        compatible = "zephyr,power-state";
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        power-state-name = "standby";
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        min-residency-us = <100000>;
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        exit-latency-us = <300>;
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    };
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};

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void main(void) {
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    init();
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    while (1) {
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        do_minimal_work();
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        WDT_kick();
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        __low_power_mode_3();   // LPM3
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    }
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}