examples/platforms/nrf52840/alarm.c

/*
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 *     derived from this software without specific prior written permission.
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/**
 * @file
 *   This file implements the OpenThread platform abstraction for the alarm.
 *
 */

#include <assert.h>
#include <stdbool.h>
#include <stdint.h>
#include <string.h>

#include <openthread/platform/alarm.h>
#include <openthread/platform/diag.h>
#include <openthread/platform/usec-alarm.h>

#include "platform-config.h"
#include "cmsis/core_cmFunc.h"

#include <drivers/clock/nrf_drv_clock.h>
#include <hal/nrf_rtc.h>

#include <openthread/config.h>
#include <openthread/types.h>

#define RTC_FREQUENCY       32768ULL

#define CEIL_DIV(A, B)      (((A) + (B) - 1ULL) / (B))

#define US_PER_MS           1000ULL
#define US_PER_S            1000000ULL
#define US_PER_TICK         CEIL_DIV(US_PER_S, RTC_FREQUENCY)

#define MS_PER_S            1000UL
#define MS_PER_OVERFLOW     (512UL * MS_PER_S)  ///< Time that has passed between overflow events. On full RTC speed, it occurs every 512 s.

typedef enum
{
    kMsTimer,
    kUsTimer,
    kNumTimers
} AlarmIndex;

typedef struct
{
    volatile bool mFireAlarm;   ///< Information for processing function, that alarm should fire.
    uint32_t      mTargetTime;  ///< Alarm fire time (in millisecond for MsTimer, in microsecond for UsTimer)
} AlarmData;

typedef struct
{
    uint32_t        mChannelNumber;
    uint32_t        mCompareEventMask;
    nrf_rtc_event_t mCompareEvent;
    nrf_rtc_int_t   mCompareInt;
} AlarmChannelData;

static volatile uint32_t sTimeOffset = 0;  ///< Time offset to keep track of current time (in millisecond).
static AlarmData sTimerData[kNumTimers];   ///< Data of the timers.
static const AlarmChannelData sChannelData[kNumTimers] =
{
    [kMsTimer] = {
        .mChannelNumber    = 0,
        .mCompareEventMask = RTC_EVTEN_COMPARE0_Msk,
        .mCompareEvent     = NRF_RTC_EVENT_COMPARE_0,
        .mCompareInt       = NRF_RTC_INT_COMPARE0_MASK,
    },
    [kUsTimer] = {
        .mChannelNumber    = 1,
        .mCompareEventMask = RTC_EVTEN_COMPARE1_Msk,
        .mCompareEvent     = NRF_RTC_EVENT_COMPARE_1,
        .mCompareInt       = NRF_RTC_INT_COMPARE1_MASK,
    }
};

static otPlatUsecAlarmHandler sUsecHandler = NULL;  ///< Handler called when usec alarm fires.
static void *sUsecContext = NULL;                   ///< The context information passed to the usec handler callback.

static void HandleOverflow(void);

static inline uint32_t TimeToTicks(uint32_t aTime, AlarmIndex aIndex)
{
    uint32_t ticks;

    if (aIndex == kMsTimer)
    {
        ticks = (uint32_t)CEIL_DIV((aTime * US_PER_MS * RTC_FREQUENCY), US_PER_S) & RTC_CC_COMPARE_Msk;
    }
    else
    {
        ticks = (uint32_t)CEIL_DIV((aTime *  RTC_FREQUENCY), US_PER_S) & RTC_CC_COMPARE_Msk;
    }

    return ticks;
}

static inline uint64_t TicksToTime(uint32_t aTicks)
{
    return CEIL_DIV((US_PER_S * (uint64_t)aTicks), RTC_FREQUENCY);
}

static inline uint64_t AlarmGetCurrentTime()
{
    uint32_t rtcValue1;
    uint32_t rtcValue2;
    uint32_t offset;

    rtcValue1 = nrf_rtc_counter_get(RTC_INSTANCE);

    __DMB();

    offset = sTimeOffset;

    __DMB();

    rtcValue2 = nrf_rtc_counter_get(RTC_INSTANCE);

    if ((rtcValue2 < rtcValue1) || (rtcValue1 == 0))
    {
        // Overflow detected. Additional condition (rtcValue1 == 0) covers situation when overflow occurred in
        // interrupt state, before this function was entered. But in general, this function shall not be called
        // from interrupt other than alarm interrupt.

        // Wait at least 20 cycles, to ensure that if interrupt is going to be called, it will be called now.
        for (uint32_t i = 0; i < 4; i++)
        {
            __NOP();
            __NOP();
            __NOP();
        }

        // If the event flag is still on, it means that the interrupt was not called, as we are in interrupt state.
        if (nrf_rtc_event_pending(RTC_INSTANCE, NRF_RTC_EVENT_OVERFLOW))
        {
            HandleOverflow();
        }

        offset = sTimeOffset;
    }

    return US_PER_MS * (uint64_t)offset + TicksToTime(rtcValue2);
}

static inline uint32_t AlarmGetCurrentTimeRtcProtected(AlarmIndex aIndex)
{
    uint64_t usecTime = AlarmGetCurrentTime() + 2 * US_PER_TICK;
    uint32_t currentTime;

    if (aIndex == kMsTimer)
    {
        currentTime = (uint32_t)(usecTime / US_PER_MS);
    }
    else
    {
        currentTime = (uint32_t)usecTime;
    }

    return currentTime;
}

static inline bool AlarmShallStrike(uint32_t aNow, AlarmIndex aIndex)
{
    uint32_t diff = aNow - sTimerData[aIndex].mTargetTime;

    // Three cases:
    // 1) aNow is before mTargetTime  =>  Difference is negative (last bit of difference is set)   => Returning false.
    // 2) aNow is same as mTargetTime =>  Difference is zero     (last bit of difference is clear) => Returning true.
    // 3) aNow is after mTargetTime   =>  Difference is positive (last bit of difference is clear) => Returning true.

    return !((diff & (1UL << 31)) != 0);
}

static void HandleCompareMatch(AlarmIndex aIndex, bool aSkipCheck)
{
    nrf_rtc_event_clear(RTC_INSTANCE, sChannelData[aIndex].mCompareEvent);

    uint64_t usecTime = AlarmGetCurrentTime();
    uint32_t now;

    if (aIndex == kMsTimer)
    {
        now = (uint32_t)(usecTime / US_PER_MS);
    }
    else
    {
        now = (uint32_t)usecTime;
    }

    // In case the target time was larger than single overflow,
    // we should only strike the timer on final compare event.
    if (aSkipCheck || AlarmShallStrike(now, aIndex))
    {
        nrf_rtc_event_disable(RTC_INSTANCE, sChannelData[aIndex].mCompareEventMask);
        nrf_rtc_int_disable(RTC_INSTANCE, sChannelData[aIndex].mCompareInt);

        sTimerData[aIndex].mFireAlarm = true;
    }
}

static void HandleOverflow(void)
{
    nrf_rtc_event_clear(RTC_INSTANCE, NRF_RTC_EVENT_OVERFLOW);

    // Increment counter on overflow.
    sTimeOffset = sTimeOffset + MS_PER_OVERFLOW;
}

static void AlarmStartAt(uint32_t aTargetTime, AlarmIndex aIndex)
{
    uint32_t targetCounter;
    uint32_t now;

    nrf_rtc_int_disable(RTC_INSTANCE, sChannelData[aIndex].mCompareInt);
    nrf_rtc_event_enable(RTC_INSTANCE, sChannelData[aIndex].mCompareEventMask);

    sTimerData[aIndex].mTargetTime = aTargetTime;

    targetCounter = TimeToTicks(sTimerData[aIndex].mTargetTime, aIndex);

    nrf_rtc_cc_set(RTC_INSTANCE, sChannelData[aIndex].mChannelNumber, targetCounter);

    now = AlarmGetCurrentTimeRtcProtected(aIndex);

    if (AlarmShallStrike(now, aIndex))
    {
        HandleCompareMatch(aIndex, true);
    }
    else
    {
        nrf_rtc_int_enable(RTC_INSTANCE, sChannelData[aIndex].mCompareInt);
    }
}

static void AlarmStop(AlarmIndex aIndex)
{
    nrf_rtc_event_disable(RTC_INSTANCE, sChannelData[aIndex].mCompareEventMask);
    nrf_rtc_int_disable(RTC_INSTANCE, sChannelData[aIndex].mCompareInt);
    nrf_rtc_event_clear(RTC_INSTANCE, sChannelData[aIndex].mCompareEvent);

    sTimerData[aIndex].mFireAlarm = false;
}

void nrf5AlarmInit(void)
{
    sTimeOffset = 0;
    memset(sTimerData, 0, sizeof(sTimerData));

    // Setup low frequency clock.
    nrf_drv_clock_lfclk_request(NULL);

    while (!nrf_drv_clock_lfclk_is_running()) {}

    // Setup RTC timer.
    NVIC_SetPriority(RTC_IRQN, RTC_IRQ_PRIORITY);
    NVIC_ClearPendingIRQ(RTC_IRQN);
    NVIC_EnableIRQ(RTC_IRQN);

    nrf_rtc_prescaler_set(RTC_INSTANCE, 0);

    nrf_rtc_event_clear(RTC_INSTANCE, NRF_RTC_EVENT_OVERFLOW);
    nrf_rtc_event_enable(RTC_INSTANCE, RTC_EVTEN_OVRFLW_Msk);
    nrf_rtc_int_enable(RTC_INSTANCE, NRF_RTC_INT_OVERFLOW_MASK);

    for (uint32_t i = 0; i < kNumTimers; i++)
    {
        nrf_rtc_event_clear(RTC_INSTANCE, sChannelData[i].mCompareEvent);
        nrf_rtc_event_disable(RTC_INSTANCE, sChannelData[i].mCompareEventMask);
        nrf_rtc_int_disable(RTC_INSTANCE, sChannelData[i].mCompareInt);
    }

    nrf_rtc_task_trigger(RTC_INSTANCE, NRF_RTC_TASK_START);
}

void nrf5AlarmDeinit(void)
{
    nrf_rtc_task_trigger(RTC_INSTANCE, NRF_RTC_TASK_STOP);

    for (uint32_t i = 0; i < kNumTimers; i++)
    {
        nrf_rtc_event_clear(RTC_INSTANCE, sChannelData[i].mCompareEvent);
        nrf_rtc_event_disable(RTC_INSTANCE, sChannelData[i].mCompareEventMask);
        nrf_rtc_int_disable(RTC_INSTANCE, sChannelData[i].mCompareInt);
    }

    nrf_rtc_int_disable(RTC_INSTANCE, NRF_RTC_INT_OVERFLOW_MASK);
    nrf_rtc_event_disable(RTC_INSTANCE, RTC_EVTEN_OVRFLW_Msk);
    nrf_rtc_event_clear(RTC_INSTANCE, NRF_RTC_EVENT_OVERFLOW);

    NVIC_DisableIRQ(RTC_IRQN);
    NVIC_ClearPendingIRQ(RTC_IRQN);
    NVIC_SetPriority(RTC_IRQN, 0);

    nrf_drv_clock_lfclk_release();
}

void nrf5AlarmProcess(otInstance *aInstance)
{
    if (sTimerData[kMsTimer].mFireAlarm)
    {
        sTimerData[kMsTimer].mFireAlarm = false;

#if OPENTHREAD_ENABLE_DIAG

        if (otPlatDiagModeGet())
        {
            otPlatDiagAlarmFired(aInstance);
        }
        else
#endif
        {
            otPlatAlarmFired(aInstance);
        }
    }

    if (sTimerData[kUsTimer].mFireAlarm)
    {
        sTimerData[kUsTimer].mFireAlarm = false;

        sUsecHandler(sUsecContext);
    }
}

uint32_t otPlatAlarmGetNow(void)
{
    return (uint32_t)(AlarmGetCurrentTime() / US_PER_MS);
}

void otPlatAlarmStartAt(otInstance *aInstance, uint32_t aT0, uint32_t aDt)
{
    (void)aInstance;
    uint32_t targetTime = aT0 + aDt;

    AlarmStartAt(targetTime, kMsTimer);
}

void otPlatAlarmStop(otInstance *aInstance)
{
    (void)aInstance;

    AlarmStop(kMsTimer);
}

uint32_t otPlatUsecAlarmGetNow(void)
{
    return (uint32_t)AlarmGetCurrentTime();
}

void otPlatUsecAlarmStartAt(otInstance *aInstance, uint32_t aT0, uint32_t aDt,
                            otPlatUsecAlarmHandler aHandler, void *aContext)
{
    (void)aInstance;
    uint32_t targetTime = aT0 + aDt;

    AlarmStartAt(targetTime, kUsTimer);

    sUsecHandler = aHandler;
    sUsecContext = aContext;
}

void otPlatUsecAlarmStop(otInstance *aInstance)
{
    (void)aInstance;

    AlarmStop(kUsTimer);
}

void RTC_IRQ_HANDLER(void)
{
    // Handle overflow.
    if (nrf_rtc_event_pending(RTC_INSTANCE, NRF_RTC_EVENT_OVERFLOW))
    {
        HandleOverflow();
    }

    // Handle compare match.
    for (uint32_t i = 0; i < kNumTimers; i++)
    {
        if (nrf_rtc_int_is_enabled(RTC_INSTANCE, sChannelData[i].mCompareInt) &&
            nrf_rtc_event_pending(RTC_INSTANCE, sChannelData[i].mCompareEvent))
        {
            HandleCompareMatch((AlarmIndex)i, false);
        }
    }
}