text: /**
   * Copyright (c) 2015 - 2018, Nordic Semiconductor ASA
   *
   * 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, except as embedded into a Nordic
   *    Semiconductor ASA integrated circuit in a product or a software update for
   *    such product, 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 Nordic Semiconductor ASA nor the names of its
   *    contributors may be used to endorse or promote products derived from this
   *    software without specific prior written permission.
   *
   * 4. This software, with or without modification, must only be used with a
   *    Nordic Semiconductor ASA integrated circuit.
   *
   * 5. Any software provided in binary form under this license must not be reverse
   *    engineered, decompiled, modified and/or disassembled.
   *
   * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
   * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY, NONINFRINGEMENT, AND FITNESS FOR A PARTICULAR PURPOSE ARE
   * DISCLAIMED. IN NO EVENT SHALL NORDIC SEMICONDUCTOR ASA 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; 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.
   *
   */
  #include "nrf_drv_spi.h"
  #include "app_util_platform.h"
  #include "nrf_gpio.h"
  #include "nrf_delay.h"
  #include "boards.h"
  #include "app_error.h"
  #include <string.h>
  #include "nrf_log.h"
  #include "nrf_log_ctrl.h"
  #include "nrf_log_default_backends.h"
  
  #define SPI_INSTANCE  0 /**< SPI instance index. */
  static const nrf_drv_spi_t spi = NRF_DRV_SPI_INSTANCE(SPI_INSTANCE);  /**< SPI instance. */
  static volatile bool spi_xfer_done;  /**< Flag used to indicate that SPI instance completed the transfer. */
  
  #define TEST_STRING "Nordic"
  static uint8_t       m_tx_buf[] = TEST_STRING;           /**< TX buffer. */
  static uint8_t       m_rx_buf[sizeof(TEST_STRING) + 1];    /**< RX buffer. */
  static const uint8_t m_length = sizeof(m_tx_buf);        /**< Transfer length. */
  
  /**
   * @brief SPI user event handler.
   * @param event
   */
  void spi_event_handler(nrf_drv_spi_evt_t const * p_event,
                         void *                    p_context)
  {
      spi_xfer_done = true;
      NRF_LOG_INFO("Transfer completed.");
      if (m_rx_buf[0] != 0)
      {
          NRF_LOG_INFO(" Received:");
          NRF_LOG_HEXDUMP_INFO(m_rx_buf, strlen((const char *)m_rx_buf));
      }
  }
  
  int main(void)
  {
      bsp_board_init(BSP_INIT_LEDS);
  
      APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
      NRF_LOG_DEFAULT_BACKENDS_INIT();
  
      nrf_drv_spi_config_t spi_config = NRF_DRV_SPI_DEFAULT_CONFIG;
      spi_config.ss_pin   = SPI_SS_PIN;
      spi_config.miso_pin = SPI_MISO_PIN;
      spi_config.mosi_pin = SPI_MOSI_PIN;
      spi_config.sck_pin  = SPI_SCK_PIN;
      APP_ERROR_CHECK(nrf_drv_spi_init(&spi, &spi_config, spi_event_handler, NULL));
  
      NRF_LOG_INFO("SPI example started.");
  
      while (1)
      {
          // Reset rx buffer and transfer done flag
          memset(m_rx_buf, 0, m_length);
          spi_xfer_done = false;
  
          APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi, m_tx_buf, m_length, m_rx_buf, m_length));
  
          while (!spi_xfer_done)
          {
              __WFE();
          }
  
          NRF_LOG_FLUSH();
  
          bsp_board_led_invert(BSP_BOARD_LED_0);
          nrf_delay_ms(200);
      }
  }
  