text: /**
   * This software is subject to the ANT+ Shared Source License
   * www.thisisant.com/swlicenses
   * Copyright (c) Dynastream Innovations, Inc. 2015
   * All rights reserved.
   * 
   * Redistribution and use in source and binary forms, with or
   * without modification, are permitted provided that the following
   * conditions are met:
   * 1) Redistributions of source code must retain the above
   *    copyright notice, this list of conditions and the following
   *    disclaimer.
   * 
   * 2) Redistributions in binary form must reproduce the above
   *    copyright notice, this list of conditions and the following
   *    disclaimer in the documentation and/or other materials
   *    provided with the distribution.
   * 
   * 3) Neither the name of Dynastream nor the names of its
   *    contributors may be used to endorse or promote products
   *    derived from this software without specific prior
   *    written permission.
   * 
   * The following actions are prohibited:
   * 1) Redistribution of source code containing the ANT+ Network
   *    Key. The ANT+ Network Key is available to ANT+ Adopters.
   *    Please refer to http://thisisant.com to become an ANT+
   *    Adopter and access the key.
   * 
   * 2) Reverse engineering, decompilation, and/or disassembly of
   *    software provided in binary form under this license.
   * 
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
   * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
   * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE HEREBY
   * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES(INCLUDING,
   * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
   * SERVICES; DAMAGE TO ANY DEVICE, LOSS OF USE, DATA, OR
   * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
   * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
   * OF THE POSSIBILITY OF SUCH DAMAGE. SOME STATES DO NOT ALLOW
   * THE EXCLUSION OF INCIDENTAL OR CONSEQUENTIAL DAMAGES, SO THE
   * ABOVE LIMITATIONS MAY NOT APPLY TO YOU.
   * 
   */
  #include "ant_async_tx.h"
  #include <stdint.h>
  #include "ant_interface.h"
  #include "ant_parameters.h"
  #include "app_timer.h"
  #include "app_error.h"
  #include "boards.h"
  #include "sdk_config.h"
  #include "ant_channel_config.h"
  #include "ant_search_config.h"
  #include "nrf_soc.h"
  
  // Miscellaneous defines.
  #define ANT_CHANNEL_DEFAULT_NETWORK    0x00                               /**< ANT Channel Network. */
  #define ANT_CHANNEL_NUMBER             0x00                               /**< ANT Channel Number. */
  
  // Application specific commands
  #define COMMAND_PAGE                   0x01                               /**< Page number for command data */
  #define COMMAND_0                      0x10                               /**< Command associated with pressing BSP_BUTTON_0 */
  #define COMMAND_1                      0x11                               /**< Command associated with pressing BSP_BUTTON_1 */
  
  // Retry configuration
  #define MAX_RETRIES                    8                                  /**< Maximum number of retries for sending a command */
  #define MIN_BACKOFF_TIME               20                                 /**< Minimum number of ms to wait before next retry attempt. The maximum back off time is 255 + MIN_BACKOFF_TIME */
  
  static uint8_t  m_cmd_tx_buffer[ANT_STANDARD_DATA_PAYLOAD_SIZE];          /**< Command data transmit buffer */
  static uint8_t  m_retries;                                                /**< Number of remaining retries */
  static uint8_t  m_sequence_number;                                        /**< Sequence number */
  
  APP_TIMER_DEF(m_backoff_timer);                                           /**< Back off timer */
  
  
  /**@brief Perform message retries
   *
   */
  static void retry_perform(void)
  {
      if (m_retries > 0)
      {
          uint32_t err_code = sd_ant_acknowledge_message_tx(ANT_CHANNEL_NUMBER,
                                                            ANT_STANDARD_DATA_PAYLOAD_SIZE,
                                                            m_cmd_tx_buffer);
          if (err_code != TRANSFER_IN_PROGRESS)
          {
              // Transfer in progress means that a message is waiting to be transmitted by ANT as an ACK.
              // Ignore this error; attempts to initiate a burst transfer while already busy handling one
              // will be ignored.
              APP_ERROR_CHECK(err_code);
          }
  
          m_retries--;
      }
  }
  
  
  /**@brief Send command over async channel
   *
   * @param[in] command   Command to send
   */
  static void async_command_send(uint8_t command)
  {
      m_cmd_tx_buffer[0] = COMMAND_PAGE;
      m_cmd_tx_buffer[1] = 0xFF;
      m_cmd_tx_buffer[2] = 0xFF;
      m_cmd_tx_buffer[3] = 0xFF;
      m_cmd_tx_buffer[4] = 0xFF;
      m_cmd_tx_buffer[5] = 0xFF;
      m_cmd_tx_buffer[6] = m_sequence_number;
      m_cmd_tx_buffer[7] = command;
      m_retries          = MAX_RETRIES;
      m_sequence_number++;
      retry_perform();
  }
  
  
  /**@brief Handler for backoff timer event
   *
   * @param[in] p_context   Pointer to context
   */
  static void backoff_timer_evt_handler(void * p_context)
  {
      retry_perform();
  }
  
  
  /**@brief Function for generating a random number using the RNG
   * The number generated is between [MIN_BACKOFF_TIME, 255 + MIN_BACKOFF_TIME] (inclusive)
   *
   */
  static uint16_t rnd_backoff_generate(void)
  {
      uint8_t  rand_bytes[1]   = {0};
      uint8_t  bytes_available = 0;
      uint32_t err_code;
      uint16_t rand_value;
  
      while (bytes_available < 1)
      {
          err_code = sd_rand_application_bytes_available_get(&bytes_available);
          APP_ERROR_CHECK(err_code);
      }
  
      err_code = sd_rand_application_vector_get(rand_bytes, 1);
      APP_ERROR_CHECK(err_code);
  
      rand_value = (uint16_t) (rand_bytes[0]) + MIN_BACKOFF_TIME;
  
      return rand_value;
  }
  
  
  void ant_async_tx_setup(void)
  {
      uint32_t err_code;
  
      ant_channel_config_t channel_config =
      {
          .channel_number    = ANT_CHANNEL_NUMBER,
          .channel_type      = CHANNEL_TYPE_MASTER,
          .ext_assign        = EXT_PARAM_ASYNC_TX_MODE | EXT_PARAM_FAST_INITIATION_MODE,
          .rf_freq           = RF_FREQ,
          .transmission_type = CHAN_ID_TRANS_TYPE,
          .device_type       = CHAN_ID_DEV_TYPE,
          .device_number     = (uint16_t) (NRF_FICR->DEVICEID[0]),
          .channel_period    = CHAN_PERIOD,
          .network_number    = ANT_CHANNEL_DEFAULT_NETWORK,
      };
  
      err_code = ant_channel_init(&channel_config);
      APP_ERROR_CHECK(err_code);
  
      m_retries         = 0;
      m_sequence_number = 0;
  
      err_code = app_timer_create(&m_backoff_timer,
                                  APP_TIMER_MODE_SINGLE_SHOT,
                                  backoff_timer_evt_handler);
      APP_ERROR_CHECK(err_code);
  }
  
  
  void ant_async_tx_bsp_evt_handler(bsp_event_t evt)
  {
      switch (evt)
      {
          case BSP_EVENT_KEY_0:
              bsp_board_led_invert(BSP_BOARD_LED_0);
              async_command_send(COMMAND_0);
              break;
  
          case BSP_EVENT_KEY_1:
              bsp_board_led_invert(BSP_BOARD_LED_0);
              async_command_send(COMMAND_1);
              break;
  
          default:
              return; // no implementation needed
      }
  }
  
  
  void ant_async_tx_event_handler(ant_evt_t * p_ant_evt)
  {
      switch (p_ant_evt->event)
      {
          case EVENT_TRANSFER_TX_COMPLETED:
              // The message was successfully transmitted
              m_retries = 0;
              break;
  
          case EVENT_TRANSFER_TX_FAILED:
              // The message failed; attempt a retry after a random backoff period
              if (m_retries > 0)
              {
                  uint32_t backoff_time = (uint32_t) rnd_backoff_generate();
  
                  uint32_t err_code =
                      app_timer_start(m_backoff_timer,
                                      APP_TIMER_TICKS(backoff_time),
                                      NULL);
                  APP_ERROR_CHECK(err_code);
              }
              break;
  
          default:
              break;
      }
  }
  
  