micro_esb.c

/* Copyright (c) 2014 Nordic Semiconductor. All Rights Reserved.
 *
 * The information contained herein is property of Nordic Semiconductor ASA.
 * Terms and conditions of usage are described in detail in NORDIC
 * SEMICONDUCTOR STANDARD SOFTWARE LICENSE AGREEMENT.
 *
 * Licensees are granted free, non-transferable use of the information. NO
 * WARRANTY of ANY KIND is provided. This heading must NOT be removed from
 * the file.
 *
 */

#include "micro_esb.h"
#include "uesb_error_codes.h"
#include "nrf_gpio.h"
#include <string.h>


static uesb_event_handler_t     m_event_handler;

// RF parameters
static uesb_config_t            m_config_local;

// TX FIFO
static uesb_payload_t           m_tx_fifo_payload[UESB_CORE_TX_FIFO_SIZE];
static uesb_payload_tx_fifo_t   m_tx_fifo;

// RX FIFO
static uesb_payload_t           m_rx_fifo_payload[UESB_CORE_RX_FIFO_SIZE];
static uesb_payload_rx_fifo_t   m_rx_fifo;

static  uint8_t                 m_tx_payload_buffer[UESB_CORE_MAX_PAYLOAD_LENGTH + 2];
static  uint8_t                 m_rx_payload_buffer[UESB_CORE_MAX_PAYLOAD_LENGTH + 2];

// Run time variables
static volatile uint32_t        m_interrupt_flags       = 0;
static uint32_t                 m_pid                   = 0;
static volatile uint32_t        m_retransmits_remaining;
static volatile uint32_t        m_last_tx_attempts;
static volatile uint8_t         m_last_rx_packet_pid = UESB_PID_RESET_VALUE;
static volatile uint32_t        m_last_rx_packet_crc = 0xFFFFFFFF;
static volatile uint32_t        m_wait_for_ack_timeout_us;

static uesb_payload_t           *current_payload;

static uesb_mainstate_t         m_uesb_mainstate        = UESB_STATE_UNINITIALIZED;

// Constant parameters
#define                         RX_WAIT_FOR_ACK_TIMEOUT_US_2MBPS   48   // Smallest reliable value - 43
#define                         RX_WAIT_FOR_ACK_TIMEOUT_US_1MBPS   64   // Smallest reliable value - 59
#define                         RX_WAIT_FOR_ACK_TIMEOUT_US_250KBPS 250

// Macros
#define                         DISABLE_RF_IRQ      NVIC_DisableIRQ(RADIO_IRQn)
#define                         ENABLE_RF_IRQ       NVIC_EnableIRQ(RADIO_IRQn)

#define                         RADIO_SHORTS_COMMON ( RADIO_SHORTS_READY_START_Msk | RADIO_SHORTS_END_DISABLE_Msk | \
                                                      RADIO_SHORTS_ADDRESS_RSSISTART_Msk | RADIO_SHORTS_DISABLED_RSSISTOP_Msk )

// These function pointers are changed dynamically, depending on protocol configuration and state
static void (*on_radio_disabled)(void) = 0;
static void (*on_radio_end)(void) = 0;
static void (*update_rf_payload_format)(uint32_t payload_length) = 0;

// The following functions are assigned to the function pointers above
static void on_radio_disabled_esb_dpl_tx_noack(void);
static void on_radio_disabled_esb_dpl_tx(void);
static void on_radio_disabled_esb_dpl_tx_wait_for_ack(void);
static void on_radio_disabled_esb_dpl_rx(void);
static void on_radio_disabled_esb_dpl_rx_ack(void);

static void on_radio_end_sb_tx(void);
static void on_radio_end_sb_rx(void);

static void update_rf_payload_format_esb_dpl(uint32_t payload_length)
{
#if(UESB_CORE_MAX_PAYLOAD_LENGTH <= 32)
    NRF_RADIO->PCNF0 = (0 << RADIO_PCNF0_S0LEN_Pos) | (6 << RADIO_PCNF0_LFLEN_Pos) | (3 << RADIO_PCNF0_S1LEN_Pos);
#else
    NRF_RADIO->PCNF0 = (0 << RADIO_PCNF0_S0LEN_Pos) | (8 << RADIO_PCNF0_LFLEN_Pos) | (3 << RADIO_PCNF0_S1LEN_Pos);
#endif
    NRF_RADIO->PCNF1 = (RADIO_PCNF1_WHITEEN_Disabled        << RADIO_PCNF1_WHITEEN_Pos) |
                       (RADIO_PCNF1_ENDIAN_Big              << RADIO_PCNF1_ENDIAN_Pos)  |
                       ((m_config_local.rf_addr_length - 1) << RADIO_PCNF1_BALEN_Pos)   |
                       (0                                   << RADIO_PCNF1_STATLEN_Pos) |
                       (UESB_CORE_MAX_PAYLOAD_LENGTH        << RADIO_PCNF1_MAXLEN_Pos);
}

static void update_rf_payload_format_esb(uint32_t payload_length)
{
    NRF_RADIO->PCNF0 = (1 << RADIO_PCNF0_S0LEN_Pos) | (0 << RADIO_PCNF0_LFLEN_Pos) | (1 << RADIO_PCNF0_S1LEN_Pos);
    NRF_RADIO->PCNF1 = (RADIO_PCNF1_WHITEEN_Disabled        << RADIO_PCNF1_WHITEEN_Pos) |
                       (RADIO_PCNF1_ENDIAN_Big              << RADIO_PCNF1_ENDIAN_Pos)  |
                       ((m_config_local.rf_addr_length - 1) << RADIO_PCNF1_BALEN_Pos)   |
                       (payload_length                      << RADIO_PCNF1_STATLEN_Pos) |
                       (payload_length                      << RADIO_PCNF1_MAXLEN_Pos);
}

static void update_rf_payload_format_sb(uint32_t payload_length)
{
    NRF_RADIO->PCNF0 = (0 << RADIO_PCNF0_S0LEN_Pos) | (0 << RADIO_PCNF0_LFLEN_Pos) | (0 << RADIO_PCNF0_S1LEN_Pos);
    NRF_RADIO->PCNF1 = (RADIO_PCNF1_WHITEEN_Disabled        << RADIO_PCNF1_WHITEEN_Pos) |
                       (RADIO_PCNF1_ENDIAN_Big              << RADIO_PCNF1_ENDIAN_Pos)  |
                       ((m_config_local.rf_addr_length - 1) << RADIO_PCNF1_BALEN_Pos)   |
                       (payload_length                      << RADIO_PCNF1_STATLEN_Pos) |
                       (payload_length                      << RADIO_PCNF1_MAXLEN_Pos);
}

// Function that swaps the bits within each byte in a uint32. Used to convert from nRF24L type addressing to nRF51 type addressing
static uint32_t bytewise_bit_swap(uint32_t inp)
{
    inp = (inp & 0xF0F0F0F0) >> 4 | (inp & 0x0F0F0F0F) << 4;
    inp = (inp & 0xCCCCCCCC) >> 2 | (inp & 0x33333333) << 2;
    return (inp & 0xAAAAAAAA) >> 1 | (inp & 0x55555555) << 1;
}

static void update_radio_parameters()
{
    // Protocol
    switch(m_config_local.protocol)
    {
        case UESB_PROTOCOL_ESB_DPL:
            update_rf_payload_format = update_rf_payload_format_esb_dpl;
            break;
        case UESB_PROTOCOL_ESB:
            update_rf_payload_format = update_rf_payload_format_esb;
            break;
        case UESB_PROTOCOL_SB:
            update_rf_payload_format = update_rf_payload_format_sb;
            on_radio_end = (m_config_local.mode == UESB_MODE_PTX ? on_radio_end_sb_tx : on_radio_end_sb_rx);
            break;
    }
    // TX power
    NRF_RADIO->TXPOWER   = m_config_local.tx_output_power   << RADIO_TXPOWER_TXPOWER_Pos;

    // RF bitrate
    NRF_RADIO->MODE      = m_config_local.bitrate           << RADIO_MODE_MODE_Pos;
    switch(m_config_local.bitrate)
    {
        case UESB_BITRATE_2MBPS:
            m_wait_for_ack_timeout_us = RX_WAIT_FOR_ACK_TIMEOUT_US_2MBPS;
            break;
        case UESB_BITRATE_1MBPS:
            m_wait_for_ack_timeout_us = RX_WAIT_FOR_ACK_TIMEOUT_US_1MBPS;
            break;
        case UESB_BITRATE_250KBPS:
            m_wait_for_ack_timeout_us = RX_WAIT_FOR_ACK_TIMEOUT_US_250KBPS;
            break;
    }

    // CRC configuration
    NRF_RADIO->CRCCNF    = m_config_local.crc               << RADIO_CRCCNF_LEN_Pos;
    if(m_config_local.crc == RADIO_CRCCNF_LEN_Two)
    {
        NRF_RADIO->CRCINIT = 0xFFFFUL;      // Initial value
        NRF_RADIO->CRCPOLY = 0x11021UL;     // CRC poly: x^16+x^12^x^5+1
    }
    else if(m_config_local.crc == RADIO_CRCCNF_LEN_One)
    {
        NRF_RADIO->CRCINIT = 0xFFUL;        // Initial value
        NRF_RADIO->CRCPOLY = 0x107UL;       // CRC poly: x^8+x^2^x^1+1
    }

    // Packet format
    update_rf_payload_format(m_config_local.payload_length);

    // Radio address config
    NRF_RADIO->PREFIX0 = bytewise_bit_swap(m_config_local.rx_address_p3 << 24 | m_config_local.rx_address_p2 << 16 | m_config_local.rx_address_p1[0] << 8 | m_config_local.rx_address_p0[0]);
    NRF_RADIO->PREFIX1 = bytewise_bit_swap(m_config_local.rx_address_p7 << 24 | m_config_local.rx_address_p6 << 16 | m_config_local.rx_address_p5 << 8 | m_config_local.rx_address_p4);
    NRF_RADIO->BASE0   = bytewise_bit_swap(m_config_local.rx_address_p0[1] << 24 | m_config_local.rx_address_p0[2] << 16 | m_config_local.rx_address_p0[3] << 8 | m_config_local.rx_address_p0[4]);
    NRF_RADIO->BASE1   = bytewise_bit_swap(m_config_local.rx_address_p1[1] << 24 | m_config_local.rx_address_p1[2] << 16 | m_config_local.rx_address_p1[3] << 8 | m_config_local.rx_address_p1[4]);
}

static void initialize_fifos()
{
    m_tx_fifo.entry_point = 0;
    m_tx_fifo.exit_point  = 0;
    m_tx_fifo.count       = 0;
    for(int i = 0; i < UESB_CORE_TX_FIFO_SIZE; i++)
    {
        m_tx_fifo.payload_ptr[i] = &m_tx_fifo_payload[i];
    }

    m_rx_fifo.entry_point = 0;
    m_rx_fifo.exit_point  = 0;
    m_rx_fifo.count       = 0;
    for(int i = 0; i < UESB_CORE_RX_FIFO_SIZE; i++)
    {
        m_rx_fifo.payload_ptr[i] = &m_rx_fifo_payload[i];
    }
}

static void tx_fifo_remove_last()
{
    if(m_tx_fifo.count > 0)
    {
        DISABLE_RF_IRQ;
        m_tx_fifo.count--;
        m_tx_fifo.exit_point++;
        if(m_tx_fifo.exit_point >= UESB_CORE_TX_FIFO_SIZE) m_tx_fifo.exit_point = 0;
        ENABLE_RF_IRQ;
    }
}

static bool rx_fifo_push_rfbuf(uint8_t pipe)
{
    if(m_rx_fifo.count < UESB_CORE_RX_FIFO_SIZE)
    {
        if(m_config_local.protocol == UESB_PROTOCOL_ESB_DPL)
        {
            if(m_rx_payload_buffer[0] > UESB_CORE_MAX_PAYLOAD_LENGTH) return false;
            m_rx_fifo.payload_ptr[m_rx_fifo.entry_point]->length = m_rx_payload_buffer[0];
        }
        else
        {
            m_rx_fifo.payload_ptr[m_rx_fifo.entry_point]->length = m_config_local.payload_length;
        }
        if(m_config_local.protocol == UESB_PROTOCOL_SB)
        {
            memcpy(m_rx_fifo.payload_ptr[m_rx_fifo.entry_point]->data, &m_rx_payload_buffer[0], m_rx_fifo.payload_ptr[m_rx_fifo.entry_point]->length);
        }
        else
        {
            memcpy(m_rx_fifo.payload_ptr[m_rx_fifo.entry_point]->data, &m_rx_payload_buffer[2], m_rx_fifo.payload_ptr[m_rx_fifo.entry_point]->length);
        }
        m_rx_fifo.payload_ptr[m_rx_fifo.entry_point]->pipe = pipe;
        m_rx_fifo.payload_ptr[m_rx_fifo.entry_point]->rssi = NRF_RADIO->RSSISAMPLE;
        if(++m_rx_fifo.entry_point >= UESB_CORE_RX_FIFO_SIZE) m_rx_fifo.entry_point = 0;
        m_rx_fifo.count++;
        return true;
    }
    return false;
}

static void sys_timer_init()
{
    // Configure the system timer with a 1 MHz base frequency
    UESB_SYS_TIMER->PRESCALER = 4;
    UESB_SYS_TIMER->BITMODE   = TIMER_BITMODE_BITMODE_16Bit;
    UESB_SYS_TIMER->SHORTS    = TIMER_SHORTS_COMPARE1_CLEAR_Msk | TIMER_SHORTS_COMPARE1_STOP_Msk;
}

static void ppi_init()
{
    NRF_PPI->CH[UESB_PPI_TIMER_START].EEP = (uint32_t)&NRF_RADIO->EVENTS_READY;
    NRF_PPI->CH[UESB_PPI_TIMER_START].TEP = (uint32_t)&UESB_SYS_TIMER->TASKS_START;
    NRF_PPI->CH[UESB_PPI_TIMER_STOP].EEP =  (uint32_t)&NRF_RADIO->EVENTS_ADDRESS;
    NRF_PPI->CH[UESB_PPI_TIMER_STOP].TEP =  (uint32_t)&UESB_SYS_TIMER->TASKS_STOP;
    NRF_PPI->CH[UESB_PPI_RX_TIMEOUT].EEP = (uint32_t)&UESB_SYS_TIMER->EVENTS_COMPARE[0];
    NRF_PPI->CH[UESB_PPI_RX_TIMEOUT].TEP = (uint32_t)&NRF_RADIO->TASKS_DISABLE;
    NRF_PPI->CH[UESB_PPI_TX_START].EEP = (uint32_t)&UESB_SYS_TIMER->EVENTS_COMPARE[1];
    NRF_PPI->CH[UESB_PPI_TX_START].TEP = (uint32_t)&NRF_RADIO->TASKS_TXEN;
}

uint32_t uesb_init(uesb_config_t *parameters)
{
    if(m_uesb_mainstate != UESB_STATE_UNINITIALIZED) return UESB_ERROR_ALREADY_INITIALIZED;
    m_event_handler = parameters->event_handler;
    memcpy(&m_config_local, parameters, sizeof(uesb_config_t));

    m_interrupt_flags    = 0;
    m_pid                = 0;
    m_last_rx_packet_pid = 0xFF;
    m_last_rx_packet_crc = 0xFFFFFFFF;

    update_radio_parameters();

    initialize_fifos();

    sys_timer_init();

    ppi_init();

    NVIC_SetPriority(RADIO_IRQn, m_config_local.radio_irq_priority & 0x03);

    //m_uesb_initialized = true;
    m_uesb_mainstate = UESB_STATE_IDLE;

    return UESB_SUCCESS;
}

uint32_t uesb_disable(void)
{
    if(m_uesb_mainstate != UESB_STATE_IDLE) return UESB_ERROR_NOT_IDLE;
    NRF_PPI->CHENCLR = (1 << UESB_PPI_TIMER_START) | (1 << UESB_PPI_TIMER_STOP) | (1 << UESB_PPI_RX_TIMEOUT) | (1 << UESB_PPI_TX_START);
    m_uesb_mainstate = UESB_STATE_UNINITIALIZED;
    return UESB_SUCCESS;
}

static void start_tx_transaction()
{
    bool ack;
    m_last_tx_attempts = 1;
    // Prepare the payload
    current_payload = m_tx_fifo.payload_ptr[m_tx_fifo.exit_point];
    m_pid = (m_pid + 1) % 4;
    switch(m_config_local.protocol)
    {
        case UESB_PROTOCOL_SB:
            update_rf_payload_format(current_payload->length);
            memcpy(&m_tx_payload_buffer[0], current_payload->data, current_payload->length);
            NRF_RADIO->SHORTS   = RADIO_SHORTS_READY_START_Msk;
            NRF_RADIO->INTENSET = RADIO_INTENSET_END_Msk;
            on_radio_disabled   = on_radio_disabled_esb_dpl_tx_noack;
            m_uesb_mainstate    = UESB_STATE_PTX_TX;
            break;

        case UESB_PROTOCOL_ESB:
            update_rf_payload_format(current_payload->length);
            m_tx_payload_buffer[0] = 0xCC | m_pid;
            m_tx_payload_buffer[1] = 0;
            memcpy(&m_tx_payload_buffer[2], current_payload->data, current_payload->length);

            NRF_RADIO->SHORTS   = RADIO_SHORTS_COMMON | RADIO_SHORTS_DISABLED_RXEN_Msk;
            NRF_RADIO->INTENSET = RADIO_INTENSET_DISABLED_Msk | RADIO_INTENSET_READY_Msk;

            // Configure the retransmit counter
            m_retransmits_remaining = m_config_local.retransmit_count;
            on_radio_disabled = on_radio_disabled_esb_dpl_tx;
            m_uesb_mainstate = UESB_STATE_PTX_TX_ACK;
            break;

        case UESB_PROTOCOL_ESB_DPL:
            ack = current_payload->noack == 0 || m_config_local.dynamic_ack_enabled == 0;
            m_tx_payload_buffer[0] = current_payload->length;
            m_tx_payload_buffer[1] = m_pid << 1 | ((current_payload->noack == 0 && m_config_local.dynamic_ack_enabled) ? 0x01 : 0x00);
            memcpy(&m_tx_payload_buffer[2], current_payload->data, current_payload->length);
            if(ack)
            {
                NRF_RADIO->SHORTS   = RADIO_SHORTS_COMMON | RADIO_SHORTS_DISABLED_RXEN_Msk;
                NRF_RADIO->INTENSET = RADIO_INTENSET_DISABLED_Msk | RADIO_INTENSET_READY_Msk;

                // Configure the retransmit counter
                m_retransmits_remaining = m_config_local.retransmit_count;
                on_radio_disabled = on_radio_disabled_esb_dpl_tx;
                m_uesb_mainstate = UESB_STATE_PTX_TX_ACK;
            }
            else
            {
                NRF_RADIO->SHORTS   = RADIO_SHORTS_COMMON;
                NRF_RADIO->INTENSET = RADIO_INTENSET_DISABLED_Msk;
                on_radio_disabled   = on_radio_disabled_esb_dpl_tx_noack;
                m_uesb_mainstate    = UESB_STATE_PTX_TX;
            }
            break;
    }

    NRF_RADIO->TXADDRESS = current_payload->pipe;
    NRF_RADIO->RXADDRESSES = 1 << current_payload->pipe;

    NRF_RADIO->FREQUENCY = m_config_local.rf_channel;

    NRF_RADIO->PACKETPTR = (uint32_t)m_tx_payload_buffer;

    NVIC_ClearPendingIRQ(RADIO_IRQn);
    NVIC_EnableIRQ(RADIO_IRQn);

    NRF_RADIO->EVENTS_ADDRESS = NRF_RADIO->EVENTS_PAYLOAD = NRF_RADIO->EVENTS_DISABLED = 0;
    DEBUG_PIN_SET(DEBUGPIN4);
    NRF_RADIO->TASKS_TXEN  = 1;
}

static uint32_t write_tx_payload(uesb_payload_t *payload, bool noack) // ~50us @ 61 bytes SB
{
    if(m_uesb_mainstate == UESB_STATE_UNINITIALIZED) return UESB_ERROR_NOT_INITIALIZED;
    if(m_tx_fifo.count >= UESB_CORE_TX_FIFO_SIZE) return UESB_ERROR_TX_FIFO_FULL;

    DISABLE_RF_IRQ;
    if(noack && m_config_local.dynamic_ack_enabled) payload->noack = 1;
    else payload->noack = 0;
    memcpy(m_tx_fifo.payload_ptr[m_tx_fifo.entry_point], payload, sizeof(uesb_payload_t));
    m_tx_fifo.entry_point++;
    if(m_tx_fifo.entry_point >= UESB_CORE_TX_FIFO_SIZE) m_tx_fifo.entry_point = 0;
    m_tx_fifo.count++;
    ENABLE_RF_IRQ;

    if(m_config_local.tx_mode == UESB_TXMODE_AUTO && m_uesb_mainstate == UESB_STATE_IDLE)
    {
        start_tx_transaction();
    }

    return UESB_SUCCESS;
}

uint32_t uesb_write_tx_payload(uesb_payload_t *payload)
{
    return write_tx_payload(payload, false);
}

uint32_t uesb_write_tx_payload_noack(uesb_payload_t *payload)
{
    if(m_config_local.dynamic_ack_enabled == 0) return UESB_ERROR_DYN_ACK_NOT_ENABLED;
    return write_tx_payload(payload, true);
}

uint32_t uesb_write_ack_payload(uesb_payload_t *payload)
{
    if(m_uesb_mainstate == UESB_STATE_UNINITIALIZED) return UESB_ERROR_NOT_INITIALIZED;
    if((m_uesb_mainstate != UESB_STATE_PRX) &&
       (m_uesb_mainstate != UESB_STATE_PRX_SEND_ACK) &&
       (m_uesb_mainstate != UESB_STATE_PRX_SEND_ACK_PAYLOAD))
    {
        return UESB_ERROR_NOT_IN_RX_MODE;
    }
    if(m_tx_fifo.count >= UESB_CORE_TX_FIFO_SIZE) return UESB_ERROR_TX_FIFO_FULL;

    DISABLE_RF_IRQ;
    memcpy(m_tx_fifo.payload_ptr[m_tx_fifo.entry_point], payload, sizeof(uesb_payload_t));
    m_tx_fifo.entry_point++;
    if(m_tx_fifo.entry_point >= UESB_CORE_TX_FIFO_SIZE) m_tx_fifo.entry_point = 0;
    m_tx_fifo.count++;
    ENABLE_RF_IRQ;

    return UESB_SUCCESS;
}

uint32_t uesb_read_rx_payload(uesb_payload_t *payload)
{
    if(m_uesb_mainstate == UESB_STATE_UNINITIALIZED) return UESB_ERROR_NOT_INITIALIZED;
    if(m_rx_fifo.count == 0) return UESB_ERROR_RX_FIFO_EMPTY;

    DISABLE_RF_IRQ;
    payload->length = m_rx_fifo.payload_ptr[m_rx_fifo.exit_point]->length;
    payload->pipe   = m_rx_fifo.payload_ptr[m_rx_fifo.exit_point]->pipe;
    payload->rssi   = m_rx_fifo.payload_ptr[m_rx_fifo.exit_point]->rssi;
    memcpy(payload->data, m_rx_fifo.payload_ptr[m_rx_fifo.exit_point]->data, payload->length);
    if(++m_rx_fifo.exit_point >= UESB_CORE_RX_FIFO_SIZE) m_rx_fifo.exit_point = 0;
    m_rx_fifo.count--;
    ENABLE_RF_IRQ;

    return UESB_SUCCESS;
}

uint32_t uesb_start_tx()
{
    if(m_uesb_mainstate != UESB_STATE_IDLE) return UESB_ERROR_NOT_IDLE;
    if(m_tx_fifo.count == 0) return UESB_ERROR_TX_FIFO_EMPTY;
    start_tx_transaction();
    return UESB_SUCCESS;
}

uint32_t uesb_start_rx(void)
{
    if(m_uesb_mainstate != UESB_STATE_IDLE) return UESB_ERROR_NOT_IDLE;

    NRF_RADIO->INTENCLR = 0xFFFFFFFF;
    NRF_RADIO->EVENTS_DISABLED = 0;
    on_radio_disabled = on_radio_disabled_esb_dpl_rx;
    switch(m_config_local.protocol)
    {
        case UESB_PROTOCOL_SB:
            NRF_RADIO->SHORTS      = RADIO_SHORTS_READY_START_Msk | RADIO_SHORTS_END_START_Msk;
            NRF_RADIO->INTENSET    = RADIO_INTENSET_END_Msk;
            m_uesb_mainstate       = UESB_STATE_PRX;
            break;
        case UESB_PROTOCOL_ESB:
            NRF_RADIO->SHORTS      = RADIO_SHORTS_COMMON | RADIO_SHORTS_DISABLED_TXEN_Msk;
            NRF_RADIO->INTENSET    = RADIO_INTENSET_DISABLED_Msk;
            m_uesb_mainstate       = UESB_STATE_PRX;
            break;
        case UESB_PROTOCOL_ESB_DPL:
            NRF_RADIO->SHORTS      = RADIO_SHORTS_COMMON | RADIO_SHORTS_DISABLED_TXEN_Msk;
            NRF_RADIO->INTENSET    = RADIO_INTENSET_DISABLED_Msk;
            m_uesb_mainstate       = UESB_STATE_PRX;
            break;
    }

    NRF_RADIO->RXADDRESSES = m_config_local.rx_pipes_enabled;

    NRF_RADIO->FREQUENCY = m_config_local.rf_channel;

    NRF_RADIO->PACKETPTR = (uint32_t)m_rx_payload_buffer;

    NVIC_ClearPendingIRQ(RADIO_IRQn);
    NVIC_EnableIRQ(RADIO_IRQn);

    NRF_RADIO->EVENTS_ADDRESS = NRF_RADIO->EVENTS_PAYLOAD = NRF_RADIO->EVENTS_DISABLED = 0;
    NRF_RADIO->TASKS_RXEN  = 1;
    return UESB_SUCCESS;
}

uint32_t uesb_stop_rx(void)
{
    if((m_uesb_mainstate == UESB_STATE_PRX) || (m_uesb_mainstate == UESB_STATE_PRX_SEND_ACK_PAYLOAD))
    {
        NRF_RADIO->SHORTS = 0;
        NRF_RADIO->INTENCLR = 0xFFFFFFFF;
        on_radio_disabled = NULL;
        NRF_RADIO->EVENTS_DISABLED = 0;
        NRF_RADIO->TASKS_DISABLE = 1;
        while(NRF_RADIO->EVENTS_DISABLED == 0);
        m_uesb_mainstate = UESB_STATE_IDLE;
        return UESB_SUCCESS;
    }
    return UESB_ERROR_NOT_IN_RX_MODE;
}

uint32_t uesb_get_tx_attempts(uint32_t *attempts)
{
    if(m_uesb_mainstate == UESB_STATE_UNINITIALIZED) return UESB_ERROR_NOT_INITIALIZED;
    *attempts = m_last_tx_attempts;
    return UESB_SUCCESS;
}

uint32_t uesb_flush_tx(void)
{
    if(m_uesb_mainstate != UESB_STATE_IDLE) return UESB_ERROR_NOT_IDLE;
    DISABLE_RF_IRQ;
    m_tx_fifo.count = 0;
    m_tx_fifo.entry_point = m_tx_fifo.exit_point = 0;
    ENABLE_RF_IRQ;
    return UESB_SUCCESS;
}

uint32_t uesb_flush_rx(void)
{
    DISABLE_RF_IRQ;
    m_rx_fifo.count = 0;
    m_last_rx_packet_pid = UESB_PID_RESET_VALUE;
    m_rx_fifo.entry_point = m_rx_fifo.exit_point = 0;
    ENABLE_RF_IRQ;
    return UESB_SUCCESS;
}

uint32_t uesb_get_clear_interrupts(uint32_t *interrupts)
{
    DISABLE_RF_IRQ;
    *interrupts = m_interrupt_flags;
    m_interrupt_flags = 0;
    ENABLE_RF_IRQ;
    return UESB_SUCCESS;
}

uint32_t uesb_set_address(uesb_address_type_t address, const uint8_t *data_ptr)
{
    if(m_uesb_mainstate != UESB_STATE_IDLE) return UESB_ERROR_NOT_IDLE;
    switch(address)
    {
        case UESB_ADDRESS_PIPE0:
            memcpy(m_config_local.rx_address_p0, data_ptr, m_config_local.rf_addr_length);
            break;
        case UESB_ADDRESS_PIPE1:
            memcpy(m_config_local.rx_address_p1, data_ptr, m_config_local.rf_addr_length);
            break;
        case UESB_ADDRESS_PIPE2:
            m_config_local.rx_address_p2 = *data_ptr;
            break;
        case UESB_ADDRESS_PIPE3:
            m_config_local.rx_address_p3 = *data_ptr;
            break;
        case UESB_ADDRESS_PIPE4:
            m_config_local.rx_address_p4 = *data_ptr;
            break;
        case UESB_ADDRESS_PIPE5:
            m_config_local.rx_address_p5 = *data_ptr;
            break;
        case UESB_ADDRESS_PIPE6:
            m_config_local.rx_address_p6 = *data_ptr;
            break;
        case UESB_ADDRESS_PIPE7:
            m_config_local.rx_address_p7 = *data_ptr;
            break;
        default:
            return UESB_ERROR_INVALID_PARAMETERS;
    }
    update_radio_parameters();
    return UESB_SUCCESS;
}

uint32_t uesb_set_rf_channel(uint32_t channel)
{
    if(channel > 125) return UESB_ERROR_INVALID_PARAMETERS;
    m_config_local.rf_channel = channel;
    return UESB_SUCCESS;
}

uint32_t uesb_set_tx_power(uesb_tx_power_t tx_output_power)
{
    if(m_uesb_mainstate != UESB_STATE_IDLE) return UESB_ERROR_NOT_IDLE;
    if ( m_config_local.tx_output_power == tx_output_power ) return UESB_SUCCESS;
    m_config_local.tx_output_power = tx_output_power;
    update_radio_parameters();
    return UESB_SUCCESS;
}

void RADIO_IRQHandler()
{
    if(NRF_RADIO->EVENTS_READY && (NRF_RADIO->INTENSET & RADIO_INTENSET_READY_Msk))
    {
        NRF_RADIO->EVENTS_READY = 0;

        DEBUG_PIN_SET(DEBUGPIN1);
    }

    if(NRF_RADIO->EVENTS_END && (NRF_RADIO->INTENSET & RADIO_INTENSET_END_Msk))
    {
        NRF_RADIO->EVENTS_END = 0;

        DEBUG_PIN_SET(DEBUGPIN2);

        // Call the correct on_radio_end function, depending on the current protocol state
        if(on_radio_end)
        {
            on_radio_end();
        }
    }

    if(NRF_RADIO->EVENTS_DISABLED && (NRF_RADIO->INTENSET & RADIO_INTENSET_DISABLED_Msk))
    {
        NRF_RADIO->EVENTS_DISABLED = 0;

        DEBUG_PIN_SET(DEBUGPIN3);

        // Call the correct on_radio_disable function, depending on the current protocol state
        if(on_radio_disabled)
        {
            on_radio_disabled();
        }
    }

    DEBUG_PIN_CLR(DEBUGPIN1);
    DEBUG_PIN_CLR(DEBUGPIN2);
    DEBUG_PIN_CLR(DEBUGPIN3);
    DEBUG_PIN_CLR(DEBUGPIN4);
}

static void on_radio_disabled_esb_dpl_tx_noack()
{
    m_interrupt_flags |= UESB_INT_TX_SUCCESS_MSK;
    tx_fifo_remove_last();

    if(m_tx_fifo.count == 0)
    {
        m_uesb_mainstate = UESB_STATE_IDLE;
    if(m_event_handler != 0) m_event_handler();
    }
    else
    {
        if(m_event_handler != 0) m_event_handler();
        start_tx_transaction();
    }
}

static void on_radio_disabled_esb_dpl_tx()
{
    // Remove the DISABLED -> RXEN shortcut, to make sure the radio stays disabled after the RX window
    NRF_RADIO->SHORTS           = RADIO_SHORTS_COMMON;

    // Make sure the timer is started the next time the radio is ready,
    // and that it will disable the radio automatically if no packet is received by the time defined in m_wait_for_ack_timeout_us
    UESB_SYS_TIMER->CC[0]       = m_wait_for_ack_timeout_us;
    UESB_SYS_TIMER->CC[1]       = m_config_local.retransmit_delay - 130;
    UESB_SYS_TIMER->TASKS_CLEAR = 1;
    UESB_SYS_TIMER->EVENTS_COMPARE[0] = 0;
    UESB_SYS_TIMER->EVENTS_COMPARE[1] = 0;
    NRF_PPI->CHENSET            = (1 << UESB_PPI_TIMER_START) | (1 << UESB_PPI_RX_TIMEOUT) | (1 << UESB_PPI_TIMER_STOP);
    NRF_PPI->CHENCLR            = (1 << UESB_PPI_TX_START);
    NRF_RADIO->EVENTS_END       = 0;
    if(m_config_local.protocol == UESB_PROTOCOL_ESB)
    {
        update_rf_payload_format(0);
    }
    NRF_RADIO->PACKETPTR        = (uint32_t)m_rx_payload_buffer;
    on_radio_disabled           = on_radio_disabled_esb_dpl_tx_wait_for_ack;
    m_uesb_mainstate            = UESB_STATE_PTX_RX_ACK;
}

static void on_radio_disabled_esb_dpl_tx_wait_for_ack()
{
    // This marks the completion of a TX_RX sequence (TX with ACK)

    // Make sure the timer will not deactivate the radio if a packet is received
    NRF_PPI->CHENCLR = (1 << UESB_PPI_TIMER_START) | (1 << UESB_PPI_RX_TIMEOUT) | (1 << UESB_PPI_TIMER_STOP);

    // If the radio has received a packet and the CRC status is OK
    if(NRF_RADIO->EVENTS_END && NRF_RADIO->CRCSTATUS != 0)
    {
        UESB_SYS_TIMER->TASKS_STOP = 1;
        NRF_PPI->CHENCLR = (1 << UESB_PPI_TX_START);
        m_interrupt_flags |= UESB_INT_TX_SUCCESS_MSK;
        m_last_tx_attempts = m_config_local.retransmit_count - m_retransmits_remaining + 1;
        tx_fifo_remove_last();
        if(m_rx_payload_buffer[0] > 0)
        {
            if(rx_fifo_push_rfbuf((uint8_t)NRF_RADIO->TXADDRESS))
            {
                m_interrupt_flags |= UESB_INT_RX_DR_MSK;
            }
        }

        if((m_tx_fifo.count == 0) || (m_config_local.tx_mode == UESB_TXMODE_MANUAL))
    {
            m_uesb_mainstate = UESB_STATE_IDLE;
        if(m_event_handler != 0) m_event_handler();
        }
        else
    {
            if(m_event_handler != 0) m_event_handler();
            start_tx_transaction();
    }
    }
    else
    {
        if(m_retransmits_remaining-- == 0)
        {
            UESB_SYS_TIMER->TASKS_STOP = 1;
            NRF_PPI->CHENCLR = (1 << UESB_PPI_TX_START);
            // All retransmits are expended, and the TX operation is suspended
            m_last_tx_attempts = m_config_local.retransmit_count + 1;
            m_interrupt_flags |= UESB_INT_TX_FAILED_MSK;

            m_uesb_mainstate = UESB_STATE_IDLE;
        if(m_event_handler != 0) m_event_handler();
        }
        else
        {
            // We still have more retransmits left, and we should enter TX mode again as soon as the system timer reaches CC[1]
            NRF_RADIO->SHORTS = RADIO_SHORTS_COMMON | RADIO_SHORTS_DISABLED_RXEN_Msk;
            update_rf_payload_format(current_payload->length);
            NRF_RADIO->PACKETPTR = (uint32_t)m_tx_payload_buffer;
            on_radio_disabled = on_radio_disabled_esb_dpl_tx;
            m_uesb_mainstate = UESB_STATE_PTX_TX_ACK;
            UESB_SYS_TIMER->TASKS_START = 1;
            NRF_PPI->CHENSET = (1 << UESB_PPI_TX_START);
            if(UESB_SYS_TIMER->EVENTS_COMPARE[1])
            {
                NRF_RADIO->TASKS_TXEN = 1;
            }                 
        }
    }
}

static void on_radio_disabled_esb_dpl_rx(void)
{
    bool send_ack = false;
    bool set_rx_interrupt = false;
    if(NRF_RADIO->CRCSTATUS != 0 && m_rx_fifo.count < UESB_CORE_RX_FIFO_SIZE)
    {
        send_ack = true;
    }
    if(send_ack)
    {
        NRF_RADIO->SHORTS = RADIO_SHORTS_COMMON | RADIO_SHORTS_DISABLED_RXEN_Msk;

        // For a packet to be considered new (and not a retransmit) the PID or the CRC has to be different
        if(NRF_RADIO->RXCRC != m_last_rx_packet_crc || (m_rx_payload_buffer[1] >> 1) != m_last_rx_packet_pid)
        {
        if((m_uesb_mainstate == UESB_STATE_PRX_SEND_ACK_PAYLOAD) && (m_tx_fifo.count > 0))
            {
                // It is assumed that the last ACK payload was recieved.
                if(++m_tx_fifo.exit_point >= UESB_CORE_RX_FIFO_SIZE) m_tx_fifo.exit_point = 0;
                m_tx_fifo.count--;

                // ACK payloads also require TX_DS (page 40 of the 'nRF24LE1_Product_Specification_rev1_6.pdf').
                m_interrupt_flags |= UESB_INT_TX_SUCCESS_MSK;
            }

            set_rx_interrupt = true;
            m_last_rx_packet_pid = m_rx_payload_buffer[1] >> 1;
            m_last_rx_packet_crc = NRF_RADIO->RXCRC;
        }

        if(m_config_local.protocol == UESB_PROTOCOL_ESB_DPL)
        {
        if(m_tx_fifo.count > 0)
        {
                current_payload = m_tx_fifo.payload_ptr[m_tx_fifo.exit_point];

                update_rf_payload_format(current_payload->length);
                m_tx_payload_buffer[0] = current_payload->length;
                memcpy(&m_tx_payload_buffer[2], current_payload->data, current_payload->length);

        m_uesb_mainstate = UESB_STATE_PRX_SEND_ACK_PAYLOAD;
        }
            else
        {
                update_rf_payload_format(0);
                m_tx_payload_buffer[0] = 0;

                m_uesb_mainstate = UESB_STATE_PRX_SEND_ACK;
            }

            m_tx_payload_buffer[1] = m_rx_payload_buffer[1];
        }
        else if(m_config_local.protocol == UESB_PROTOCOL_ESB)
        {
            m_tx_payload_buffer[0] = m_rx_payload_buffer[0];
            m_tx_payload_buffer[1] = 0;

            m_uesb_mainstate = UESB_STATE_PRX_SEND_ACK;
        }

        NRF_RADIO->TXADDRESS = NRF_RADIO->RXMATCH;
        NRF_RADIO->PACKETPTR = (uint32_t)m_tx_payload_buffer;

        on_radio_disabled = on_radio_disabled_esb_dpl_rx_ack;
    }
    else
    {
        NRF_RADIO->SHORTS = RADIO_SHORTS_COMMON;
        update_rf_payload_format(m_config_local.payload_length);
        NRF_RADIO->PACKETPTR = (uint32_t)m_rx_payload_buffer;
        NRF_RADIO->EVENTS_DISABLED = 0;
        NRF_RADIO->TASKS_DISABLE = 1;
        while(NRF_RADIO->EVENTS_DISABLED == 0);
        NRF_RADIO->EVENTS_DISABLED = 0;
        NRF_RADIO->SHORTS = RADIO_SHORTS_COMMON | RADIO_SHORTS_DISABLED_TXEN_Msk;
        NRF_RADIO->TASKS_RXEN = 1;
    }
    if(set_rx_interrupt)
    {
        rx_fifo_push_rfbuf(NRF_RADIO->RXMATCH);
        m_interrupt_flags |= UESB_INT_RX_DR_MSK;
        if(m_event_handler != 0) m_event_handler();
    }
}

static void on_radio_disabled_esb_dpl_rx_ack(void)
{
    NRF_RADIO->SHORTS = RADIO_SHORTS_COMMON | RADIO_SHORTS_DISABLED_TXEN_Msk;
    update_rf_payload_format(m_config_local.payload_length);
    NRF_RADIO->PACKETPTR = (uint32_t)m_rx_payload_buffer;
    on_radio_disabled = on_radio_disabled_esb_dpl_rx;

    if(m_uesb_mainstate == UESB_STATE_PRX_SEND_ACK)
    {
        // In the case of UESB_STATE_PRX_SEND_ACK_PAYLOAD the state will be updated when the next packet is received.
        m_uesb_mainstate = UESB_STATE_PRX;
    }
}

static void on_radio_end_sb_tx(void)
{
    m_interrupt_flags |= UESB_INT_TX_SUCCESS_MSK;
    tx_fifo_remove_last();
    if(m_config_local.tx_mode == UESB_TXMODE_MANUAL || m_tx_fifo.count == 0)
    {
        // No more packets to send. Disable the radio and set the state to idle.
        NRF_RADIO->EVENTS_DISABLED = 0;
        NRF_RADIO->TASKS_DISABLE = 1;
        while(!NRF_RADIO->EVENTS_DISABLED);
        NRF_RADIO->EVENTS_DISABLED = 0;
        m_uesb_mainstate = UESB_STATE_IDLE;
        if(m_event_handler != 0) m_event_handler();
    }
    else
    {
        // Send another packet automatically without disabling the radio first.
        current_payload = m_tx_fifo.payload_ptr[m_tx_fifo.exit_point];

        update_rf_payload_format(current_payload->length);
        memcpy(&m_tx_payload_buffer[0], current_payload->data, current_payload->length);

        NRF_RADIO->TXADDRESS = current_payload->pipe;

        NVIC_ClearPendingIRQ(RADIO_IRQn);
        NVIC_EnableIRQ(RADIO_IRQn);

        NRF_RADIO->EVENTS_ADDRESS = NRF_RADIO->EVENTS_PAYLOAD = 0;
        NRF_RADIO->TASKS_START = 1;

    }
}

static void on_radio_end_sb_rx(void)
{
    if(NRF_RADIO->CRCSTATUS != 0 && rx_fifo_push_rfbuf(NRF_RADIO->RXMATCH))
    {
        m_interrupt_flags |= UESB_INT_RX_DR_MSK;
        if(m_event_handler != 0) m_event_handler();
    }
}