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/**
 * @file
 *   This file implements CSMA-CA procedure for the 802.15.4 driver.
 *
 */

#include "nrf_802154_csma_ca.h"

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

#include "nrf_802154_config.h"
#include "nrf_802154_const.h"
#include "nrf_802154_debug.h"
#include "nrf_802154_notification.h"
#include "nrf_802154_request.h"
#include "timer_scheduler/nrf_802154_timer_sched.h"

#if NRF_802154_CSMA_CA_ENABLED

static uint8_t m_nb;                    ///< The number of times the CSMA-CA algorithm was required to back off while attempting the current transmission.
static uint8_t m_be;                    ///< Backoff exponent, which is related to how many backoff periods a device shall wait before attempting to assess a channel.

static const uint8_t    * mp_psdu;      ///< Pointer to PSDU of the frame being transmitted.
static nrf_802154_timer_t m_timer;      ///< Timer used to back off during CSMA-CA procedure.
static bool               m_is_running; ///< Indicates if CSMA-CA procedure is running.

/**
 * @brief Perform appropriate actions for busy channel conditions.
 *
 * According to CSMA-CA description in 802.15.4 specification, when channel is busy NB and BE shall
 * be incremented and the device shall wait random delay before next CCA procedure. If NB reaches
 * macMaxCsmaBackoffs procedure fails.
 *
 * @retval true   Procedure failed and TX failure should be notified to the next higher layer.
 * @retval false  Procedure is still ongoing and TX failure should be handled internally.
 */
static bool channel_busy(void);

/**
 * @brief Check if CSMA-CA is ongoing.
 *
 * @retval true   CSMA-CA is running.
 * @retval false  CSMA-CA is not running currently.
 */
static bool procedure_is_running(void)
{
    return m_is_running;
}

/**
 * @brief Stop CSMA-CA procedure.
 */
static void procedure_stop(void)
{
    m_is_running = false;
}

/**
 * Notify MAC layer that channel is busy if tx request failed and there are no retries left.
 *
 * @param[in]  result  Result of TX request.
 */
static void notify_busy_channel(bool result)
{
    if (!result && (m_nb >= (NRF_802154_CSMA_CA_MAX_CSMA_BACKOFFS - 1)))
    {
        nrf_802154_notify_transmit_failed(mp_psdu, NRF_802154_TX_ERROR_BUSY_CHANNEL);
    }
}

/**
 * @brief Perform CCA procedure followed by frame transmission.
 *
 * If transmission is requested, CSMA-CA module waits for notification from the FSM module.
 * If transmission request fails, CSMA-CA module performs procedure for busy channel condition
 * @sa channel_busy().
 *
 * @param[in] p_context  Unused variable passed from the Timer Scheduler module.
 */
static void frame_transmit(void * p_context)
{
    (void)p_context;

    nrf_802154_log(EVENT_TRACE_ENTER, FUNCTION_CSMA_FRAME_TRANSMIT);

    if (procedure_is_running())
    {
        if (!nrf_802154_request_transmit(NRF_802154_TERM_NONE,
                                         REQ_ORIG_CSMA_CA,
                                         mp_psdu,
                                         true,
                                         true,
                                         notify_busy_channel))
        {
            (void)channel_busy();
        }
    }

    nrf_802154_log(EVENT_TRACE_EXIT, FUNCTION_CSMA_FRAME_TRANSMIT);
}

/**
 * @brief Delay CCA procedure for random (2^BE - 1) unit backoff periods.
 */
static void random_backoff_start(void)
{
    uint8_t backoff_periods = rand() % (1 << m_be);

    m_timer.callback  = frame_transmit;
    m_timer.p_context = NULL;
    m_timer.t0        = nrf_802154_timer_sched_time_get();
    m_timer.dt        = backoff_periods * UNIT_BACKOFF_PERIOD;

    nrf_802154_timer_sched_add(&m_timer, false);
}

static bool channel_busy(void)
{
    bool result = true;

    if (procedure_is_running())
    {
        nrf_802154_log(EVENT_TRACE_ENTER, FUNCTION_CSMA_CHANNEL_BUSY);

        m_nb++;

        if (m_be < NRF_802154_CSMA_CA_MAX_BE)
        {
            m_be++;
        }

        if (m_nb < NRF_802154_CSMA_CA_MAX_CSMA_BACKOFFS)
        {
            random_backoff_start();
            result = false;
        }
        else
        {
            procedure_stop();
        }

        nrf_802154_log(EVENT_TRACE_EXIT, FUNCTION_CSMA_CHANNEL_BUSY);
    }

    return result;
}

void nrf_802154_csma_ca_start(const uint8_t * p_data)
{
    assert(!procedure_is_running());

    mp_psdu      = p_data;
    m_nb         = 0;
    m_be         = NRF_802154_CSMA_CA_MIN_BE;
    m_is_running = true;

    random_backoff_start();
}

bool nrf_802154_csma_ca_abort(nrf_802154_term_t term_lvl, req_originator_t req_orig)
{
    bool result = false;

    // Stop CSMA-CA only if request by the core or the higher layer.
    if ((req_orig != REQ_ORIG_CORE) && (req_orig != REQ_ORIG_HIGHER_LAYER))
    {
        return true;
    }

    nrf_802154_log(EVENT_TRACE_ENTER, FUNCTION_CSMA_ABORT);

    if (term_lvl >= NRF_802154_TERM_802154)
    {
        // Stop CSMA-CA if termination level is high enough.
        nrf_802154_timer_sched_remove(&m_timer);
        procedure_stop();

        result = true;
    }
    else if (!procedure_is_running())
    {
        // Return success in case procedure is already stopped.
        result = true;
    }

    nrf_802154_log(EVENT_TRACE_EXIT, FUNCTION_CSMA_ABORT);

    return result;
}

bool nrf_802154_csma_ca_tx_failed_hook(const uint8_t * p_frame, nrf_802154_tx_error_t error)
{
    (void)error;

    bool result = true;

    if (p_frame == mp_psdu)
    {
        nrf_802154_log(EVENT_TRACE_ENTER, FUNCTION_CSMA_TX_FAILED);

        result = channel_busy();

        nrf_802154_log(EVENT_TRACE_EXIT, FUNCTION_CSMA_TX_FAILED);
    }

    return result;
}

bool nrf_802154_csma_ca_tx_started_hook(const uint8_t * p_frame)
{
    if (p_frame == mp_psdu)
    {
        nrf_802154_log(EVENT_TRACE_ENTER, FUNCTION_CSMA_TX_STARTED);

        assert(!nrf_802154_timer_sched_is_running(&m_timer));
        procedure_stop();

        nrf_802154_log(EVENT_TRACE_EXIT, FUNCTION_CSMA_TX_STARTED);
    }

    return true;
}

#endif // NRF_802154_CSMA_CA_ENABLED