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Trouble migrating UART app from nRF52DK to nRF52810

I have been developing a bluetooth application that extends the ble_app_uart example, in SDK v14.x.x, on the nRF52 DK. I've been waiting for a custom built external board to arrive, which uses an nRF52810 chip. I can successfully program my external device using a TAG cable with a "heartbeat" program, flashing an onboard LED two times (connected to GPIO port) upon power up. The bluetooth uart application works when I download onto my nRF52 DK, I can connect to the DK using an iphone application and send/receive data. However, downloading and running the same application on my external device with an nRF52810 causes a fatal error when calling "app_timer_init()" in main.

While developing the application, I created a duplicate of the pca10040e folder within the original SDK example ble_app_uart which uses softdevice s112. I've double checked the memory settings are correct. The application advertises itself and can be recognized by my smart phone (erase all memory from nRF52DK, flash program to external board not using debugger, is detected by phone) but hangs when I attempt to make a connection. When I run the debugger, I get a fatal error produced by calling app_timer_init(), and the last call before the error handler is within "APP_UART_FIFO_HANDLER".

Below are images of my program's output when succesfully connected to the nRF52 DK, and the error screenshot when attempting to run on the external nRF52810.

Working nRF52 DK debug screen capture^^^

nRf52810 debug screen error capture ^^^^^^

_______

My main.c is included below. Can somebody help me narrow down this error, or figure out what is causing it? Unsure as to why the application works on my nRF52 DK but not nRF52810, I thought developing in the pca10040e environment is what one should do to develop nRF52810 applications.

_______

/**
 * Copyright (c) 2014 - 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.
 *
 */
/** @file
 *
 * @defgroup ble_sdk_uart_over_ble_main main.c
 * @{
 * @ingroup  ble_sdk_app_nus_eval
 * @brief    UART over BLE application main file.
 *
 * This file contains the source code for a sample application that uses the Nordic UART service.
 * This application uses the @ref srvlib_conn_params module.
 */


#include <stdint.h>
#include <string.h>
#include "nordic_common.h"
#include "nrf.h"
#include "ble_hci.h"
#include "ble_advdata.h"
#include "ble_advertising.h"
#include "ble_conn_params.h"
#include "nrf_sdh.h"
#include "nrf_sdh_soc.h"
#include "nrf_sdh_ble.h"
#include "nrf_ble_gatt.h"
#include "nrf_ble_qwr.h"
#include "app_timer.h"
#include "ble_nus.h"
#include "app_uart.h"
#include "app_util_platform.h"
#include "bsp_btn_ble.h"
#include "nrf_pwr_mgmt.h"
#include "nrf_saadc.h"
#include "nrfx_ppi.h"
#include "app_fifo.h"
#include "nrfx_pwm.h"
#include "nrf_drv_clock.h"
#include "nrf_delay.h"
#include "app_pwm.h"
#include "nrf_drv_gpiote.h"

/* SAADC Includes */
#include <string.h>
#include "nrf_drv_saadc.h"
#include "nrf_drv_ppi.h"
#include "nrf_drv_timer.h"
#include "boards.h"
#include "app_error.h"
#include "nrf_delay.h"
#include "app_util_platform.h"
#include "nrf_pwr_mgmt.h"
#include "nrfx_saadc.h"
#include "nrfx_ppi.h"

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

#if defined (UART_PRESENT)
#include "nrf_uart.h"
#endif
#if defined (UARTE_PRESENT)
#include "nrf_uarte.h"
#endif

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

#define APP_BLE_CONN_CFG_TAG            1                                           /**< A tag identifying the SoftDevice BLE configuration. */

#define DEVICE_NAME                     "UCHU_PH_SYSTEM"                            /**< Name of device. Will be included in the advertising data. */
#define NUS_SERVICE_UUID_TYPE           BLE_UUID_TYPE_VENDOR_BEGIN                  /**< UUID type for the Nordic UART Service (vendor specific). */

#define APP_BLE_OBSERVER_PRIO           3                                           /**< Application's BLE observer priority. You shouldn't need to modify this value. */

#define APP_ADV_INTERVAL                64                                          /**< The advertising interval (in units of 0.625 ms. This value corresponds to 40 ms). */

#define APP_ADV_DURATION                18000                                       /**< The advertising duration (180 seconds) in units of 10 milliseconds. */

#define MIN_CONN_INTERVAL               MSEC_TO_UNITS(20, UNIT_1_25_MS)             /**< Minimum acceptable connection interval (20 ms), Connection interval uses 1.25 ms units. */
#define MAX_CONN_INTERVAL               MSEC_TO_UNITS(75, UNIT_1_25_MS)             /**< Maximum acceptable connection interval (75 ms), Connection interval uses 1.25 ms units. */
#define SLAVE_LATENCY                   0                                           /**< Slave latency. */
#define CONN_SUP_TIMEOUT                MSEC_TO_UNITS(4000, UNIT_10_MS)             /**< Connection supervisory timeout (4 seconds), Supervision Timeout uses 10 ms units. */
#define FIRST_CONN_PARAMS_UPDATE_DELAY  APP_TIMER_TICKS(5000)                       /**< Time from initiating event (connect or start of notification) to first time sd_ble_gap_conn_param_update is called (5 seconds). */
#define NEXT_CONN_PARAMS_UPDATE_DELAY   APP_TIMER_TICKS(30000)                      /**< Time between each call to sd_ble_gap_conn_param_update after the first call (30 seconds). */
#define MAX_CONN_PARAMS_UPDATE_COUNT    3                                           /**< Number of attempts before giving up the connection parameter negotiation. */

#define DEAD_BEEF                       0xDEADBEEF                                  /**< Value used as error code on stack dump, can be used to identify stack location on stack unwind. */

#define UART_TX_BUF_SIZE                256                                         /**< UART TX buffer size. */
#define UART_RX_BUF_SIZE                256                                         /**< UART RX buffer size. */

BLE_NUS_DEF(m_nus, NRF_SDH_BLE_TOTAL_LINK_COUNT);                                   /**< BLE NUS service instance. */
NRF_BLE_GATT_DEF(m_gatt);                                                           /**< GATT module instance. */
NRF_BLE_QWR_DEF(m_qwr);                                                             /**< Context for the Queued Write module.*/
BLE_ADVERTISING_DEF(m_advertising);                                                 /**< Advertising module instance. */
APP_TIMER_DEF(m_timer_id);
APP_PWM_INSTANCE(m_isfet_pwm, 2);                                                    // Create the instance "PWM1" using TIMER1.

static uint16_t   m_conn_handle          = BLE_CONN_HANDLE_INVALID;                 /**< Handle of the current connection. */
static uint16_t   m_ble_nus_max_data_len = BLE_GATT_ATT_MTU_DEFAULT - 3;            /**< Maximum length of data (in bytes) that can be transmitted to the peer by the Nordic UART service module. */
static ble_uuid_t m_adv_uuids[]          =                                          /**< Universally unique service identifier. */
{
    {BLE_UUID_NUS_SERVICE, NUS_SERVICE_UUID_TYPE}
};

bool CONNECTION_MADE = false;

#define HEARTBEAT_PIN 15

// Forward declarations
void enable_isfet_pwm           (void);
void disable_isfet_pwm          (void);
void init_and_start_pwm         (void);
void uninit_pwm                 (void);
void enable_pH_voltage_reading  (void);

/* * * * * HEARTBEAT FUNCTIONS * * * * * *
 *
 * For debugging purposes only.
 *
 * Flashes on-board LED (UCHU RF Board R1)
 * two times upon main entry.
 */
  /* This function sets enable pin for ISFET circuitry to HIGH
  */
void led_on(void)
{
      nrf_drv_gpiote_out_config_t config = NRFX_GPIOTE_CONFIG_OUT_SIMPLE(false);
      nrf_drv_gpiote_out_init(HEARTBEAT_PIN, &config);
      nrf_drv_gpiote_out_set(HEARTBEAT_PIN);
}

/* This function sets enable pin for ISFET circuitry LOW
 */
void led_off(void)
{
     nrfx_gpiote_uninit();
}

void run_heartbeat(void)
{
    ret_code_t err_code;
    err_code = nrf_drv_gpiote_init();
    APP_ERROR_CHECK(err_code);

    for(int i = 0; i < 2; i++) {
      nrf_delay_ms(100);
      led_on();
      nrf_delay_ms(100);
      led_off();
    }
}

/* * * * * END HEARTBEAT FUNCTIONS * * * */


/**@brief Function for assert macro callback.
 *
 * @details This function will be called in case of an assert in the SoftDevice.
 *
 * @warning This handler is an example only and does not fit a final product. You need to analyse
 *          how your product is supposed to react in case of Assert.
 * @warning On assert from the SoftDevice, the system can only recover on reset.
 *
 * @param[in] line_num    Line number of the failing ASSERT call.
 * @param[in] p_file_name File name of the failing ASSERT call.
 */
void assert_nrf_callback(uint16_t line_num, const uint8_t * p_file_name)
{
    app_error_handler(DEAD_BEEF, line_num, p_file_name);
}

/**@brief Function for initializing the timer module.
 */
ret_code_t TIMER_err_code;

static void timers_init(void)
{
    TIMER_err_code = app_timer_init();
    APP_ERROR_CHECK(TIMER_err_code);
}


/**@brief Function for the GAP initialization.
 *
 * @details This function will set up all the necessary GAP (Generic Access Profile) parameters of
 *          the device. It also sets the permissions and appearance.
 */
static void gap_params_init(void)
{
    uint32_t                err_code;
    ble_gap_conn_params_t   gap_conn_params;
    ble_gap_conn_sec_mode_t sec_mode;

    BLE_GAP_CONN_SEC_MODE_SET_OPEN(&sec_mode);

    err_code = sd_ble_gap_device_name_set(&sec_mode,
                                          (const uint8_t *) DEVICE_NAME,
                                          strlen(DEVICE_NAME));
    APP_ERROR_CHECK(err_code);

    memset(&gap_conn_params, 0, sizeof(gap_conn_params));

    gap_conn_params.min_conn_interval = MIN_CONN_INTERVAL;
    gap_conn_params.max_conn_interval = MAX_CONN_INTERVAL;
    gap_conn_params.slave_latency     = SLAVE_LATENCY;
    gap_conn_params.conn_sup_timeout  = CONN_SUP_TIMEOUT;

    err_code = sd_ble_gap_ppcp_set(&gap_conn_params);
    APP_ERROR_CHECK(err_code);
}


/**@brief Function for handling Queued Write Module errors.
 *
 * @details A pointer to this function will be passed to each service which may need to inform the
 *          application about an error.
 *
 * @param[in]   nrf_error   Error code containing information about what went wrong.
 */
static void nrf_qwr_error_handler(uint32_t nrf_error)
{
    APP_ERROR_HANDLER(nrf_error);
}


/**@brief Function for handling the data from the Nordic UART Service.
 *
 * @details This function will process the data received from the Nordic UART BLE Service and send
 *          it to the UART module.
 *
 * @param[in] p_evt       Nordic UART Service event.
 */
/**@snippet [Handling the data received over BLE] */
static void nus_data_handler(ble_nus_evt_t * p_evt)
{

    if (p_evt->type == BLE_NUS_EVT_RX_DATA)
    {
        uint32_t err_code;

        NRF_LOG_DEBUG("Received data from BLE NUS. Writing data on UART.");
        NRF_LOG_HEXDUMP_DEBUG(p_evt->params.rx_data.p_data, p_evt->params.rx_data.length);

        for (uint32_t i = 0; i < p_evt->params.rx_data.length; i++)
        {
            do
            {
                err_code = app_uart_put(p_evt->params.rx_data.p_data[i]);
                if ((err_code != NRF_SUCCESS) && (err_code != NRF_ERROR_BUSY))
                {
                    NRF_LOG_ERROR("Failed receiving NUS message. Error 0x%x. ", err_code);
                    APP_ERROR_CHECK(err_code);
                }
            } while (err_code == NRF_ERROR_BUSY);
        }
        if (p_evt->params.rx_data.p_data[p_evt->params.rx_data.length - 1] == '\r')
        {
            while (app_uart_put('\n') == NRF_ERROR_BUSY);
        }
    }

}
/**@snippet [Handling the data received over BLE] */


/**@brief Function for initializing services that will be used by the application.
 */
static void services_init(void)
{
    uint32_t           err_code;
    ble_nus_init_t     nus_init;
    nrf_ble_qwr_init_t qwr_init = {0};

    // Initialize Queued Write Module.
    qwr_init.error_handler = nrf_qwr_error_handler;

    err_code = nrf_ble_qwr_init(&m_qwr, &qwr_init);
    APP_ERROR_CHECK(err_code);

    // Initialize NUS.
    memset(&nus_init, 0, sizeof(nus_init));

    nus_init.data_handler = nus_data_handler;

    err_code = ble_nus_init(&m_nus, &nus_init);
    APP_ERROR_CHECK(err_code);
}


/**@brief Function for handling an event from the Connection Parameters Module.
 *
 * @details This function will be called for all events in the Connection Parameters Module
 *          which are passed to the application.
 *
 * @note All this function does is to disconnect. This could have been done by simply setting
 *       the disconnect_on_fail config parameter, but instead we use the event handler
 *       mechanism to demonstrate its use.
 *
 * @param[in] p_evt  Event received from the Connection Parameters Module.
 */
static void on_conn_params_evt(ble_conn_params_evt_t * p_evt)
{
    uint32_t err_code;

    if (p_evt->evt_type == BLE_CONN_PARAMS_EVT_FAILED)
    {
        err_code = sd_ble_gap_disconnect(m_conn_handle, BLE_HCI_CONN_INTERVAL_UNACCEPTABLE);
        APP_ERROR_CHECK(err_code);
    }
}


/**@brief Function for handling errors from the Connection Parameters module.
 *
 * @param[in] nrf_error  Error code containing information about what went wrong.
 */
static void conn_params_error_handler(uint32_t nrf_error)
{
    APP_ERROR_HANDLER(nrf_error);
}


/**@brief Function for initializing the Connection Parameters module.
 */
static void conn_params_init(void)
{
    uint32_t               err_code;
    ble_conn_params_init_t cp_init;

    memset(&cp_init, 0, sizeof(cp_init));

    cp_init.p_conn_params                  = NULL;
    cp_init.first_conn_params_update_delay = FIRST_CONN_PARAMS_UPDATE_DELAY;
    cp_init.next_conn_params_update_delay  = NEXT_CONN_PARAMS_UPDATE_DELAY;
    cp_init.max_conn_params_update_count   = MAX_CONN_PARAMS_UPDATE_COUNT;
    cp_init.start_on_notify_cccd_handle    = BLE_GATT_HANDLE_INVALID;
    cp_init.disconnect_on_fail             = false;
    cp_init.evt_handler                    = on_conn_params_evt;
    cp_init.error_handler                  = conn_params_error_handler;

    err_code = ble_conn_params_init(&cp_init);
    APP_ERROR_CHECK(err_code);
}


/**@brief Function for putting the chip into sleep mode.
 *
 * @note This function will not return.
 */
static void sleep_mode_enter(void)
{
    uint32_t err_code = bsp_indication_set(BSP_INDICATE_IDLE);
    APP_ERROR_CHECK(err_code);

    // Prepare wakeup buttons.
    err_code = bsp_btn_ble_sleep_mode_prepare();
    APP_ERROR_CHECK(err_code);

    // Go to system-off mode (this function will not return; wakeup will cause a reset).
    err_code = sd_power_system_off();
    APP_ERROR_CHECK(err_code);
}


/**@brief Function for handling advertising events.
 *
 * @details This function will be called for advertising events which are passed to the application.
 *
 * @param[in] ble_adv_evt  Advertising event.
 */
static void on_adv_evt(ble_adv_evt_t ble_adv_evt)
{
    uint32_t err_code;

    switch (ble_adv_evt)
    {
        case BLE_ADV_EVT_FAST:
            err_code = bsp_indication_set(BSP_INDICATE_ADVERTISING);
            APP_ERROR_CHECK(err_code);
            break;
        case BLE_ADV_EVT_IDLE:
            sleep_mode_enter();
            break;
        default:
            break;
    }
}


/**@brief Function for handling BLE events.
 *
 * @param[in]   p_ble_evt   Bluetooth stack event.
 * @param[in]   p_context   Unused.
 */
static void ble_evt_handler(ble_evt_t const * p_ble_evt, void * p_context)
{
    uint32_t err_code;

    switch (p_ble_evt->header.evt_id)
    {
        case BLE_GAP_EVT_CONNECTED:
            err_code = bsp_indication_set(BSP_INDICATE_CONNECTED);
            APP_ERROR_CHECK(err_code);
            m_conn_handle = p_ble_evt->evt.gap_evt.conn_handle;
            err_code = nrf_ble_qwr_conn_handle_assign(&m_qwr, m_conn_handle);
            APP_ERROR_CHECK(err_code);
            CONNECTION_MADE = true;

            NRF_LOG_INFO("CONNECTION MADE \n");

            break;

        case BLE_GAP_EVT_DISCONNECTED:
            if(p_ble_evt->evt.gap_evt.params.disconnected.reason  == BLE_HCI_CONNECTION_TIMEOUT)
            {
                //disconnect_reason is BLE_HCI_CONNECTION_TIMEOUT
                NRF_LOG_INFO("connection timeout\n");
            }
            // LED indication will be changed when advertising starts.
            m_conn_handle = BLE_CONN_HANDLE_INVALID;
            CONNECTION_MADE = false;
            NRF_LOG_INFO("DISCONNECTED...\n");
            break;

        case BLE_GAP_EVT_PHY_UPDATE_REQUEST:
        {
            NRF_LOG_DEBUG("PHY update request.");
            ble_gap_phys_t const phys =
            {
                .rx_phys = BLE_GAP_PHY_AUTO,
                .tx_phys = BLE_GAP_PHY_AUTO,
            };
            err_code = sd_ble_gap_phy_update(p_ble_evt->evt.gap_evt.conn_handle, &phys);
            APP_ERROR_CHECK(err_code);
        } break;

        case BLE_GAP_EVT_SEC_PARAMS_REQUEST:
            // Pairing not supported
            err_code = sd_ble_gap_sec_params_reply(m_conn_handle, BLE_GAP_SEC_STATUS_PAIRING_NOT_SUPP, NULL, NULL);
            APP_ERROR_CHECK(err_code);
            break;

        case BLE_GATTS_EVT_SYS_ATTR_MISSING:
            // No system attributes have been stored.
            err_code = sd_ble_gatts_sys_attr_set(m_conn_handle, NULL, 0, 0);
            APP_ERROR_CHECK(err_code);
            break;

        case BLE_GATTC_EVT_TIMEOUT:
            // Disconnect on GATT Client timeout event.
            err_code = sd_ble_gap_disconnect(p_ble_evt->evt.gattc_evt.conn_handle,
                                             BLE_HCI_REMOTE_USER_TERMINATED_CONNECTION);
            CONNECTION_MADE = false;
            APP_ERROR_CHECK(err_code);
            break;

        case BLE_GATTS_EVT_TIMEOUT:
            // Disconnect on GATT Server timeout event.
            err_code = sd_ble_gap_disconnect(p_ble_evt->evt.gatts_evt.conn_handle,
                                             BLE_HCI_REMOTE_USER_TERMINATED_CONNECTION);
            CONNECTION_MADE = false;
            APP_ERROR_CHECK(err_code);
            break;

        default:
            // No implementation needed.
            break;
    }
}


/**@brief Function for the SoftDevice initialization.
 *
 * @details This function initializes the SoftDevice and the BLE event interrupt.
 */
static void ble_stack_init(void)
{
    ret_code_t err_code;

    err_code = nrf_sdh_enable_request();
    APP_ERROR_CHECK(err_code);

    // Configure the BLE stack using the default settings.
    // Fetch the start address of the application RAM.
    uint32_t ram_start = 0;
    err_code = nrf_sdh_ble_default_cfg_set(APP_BLE_CONN_CFG_TAG, &ram_start);
    APP_ERROR_CHECK(err_code);

    // Enable BLE stack.
    err_code = nrf_sdh_ble_enable(&ram_start);
    APP_ERROR_CHECK(err_code);

    // Register a handler for BLE events.
    NRF_SDH_BLE_OBSERVER(m_ble_observer, APP_BLE_OBSERVER_PRIO, ble_evt_handler, NULL);
}



/**@brief Function for handling events from the BSP module.
 *
 * @param[in]   event   Event generated by button press.
 */
void bsp_event_handler(bsp_event_t event)
{
    uint32_t err_code;
    switch (event)
    {
        case BSP_EVENT_SLEEP:
            sleep_mode_enter();
            break;

        case BSP_EVENT_DISCONNECT:
            err_code = sd_ble_gap_disconnect(m_conn_handle, BLE_HCI_REMOTE_USER_TERMINATED_CONNECTION);
            if (err_code != NRF_ERROR_INVALID_STATE)
            {
                APP_ERROR_CHECK(err_code);
            }
            break;

        case BSP_EVENT_WHITELIST_OFF:
            if (m_conn_handle == BLE_CONN_HANDLE_INVALID)
            {
                err_code = ble_advertising_restart_without_whitelist(&m_advertising);
                if (err_code != NRF_ERROR_INVALID_STATE)
                {
                    APP_ERROR_CHECK(err_code);
                }
            }
            break;

        default:
            break;
    }
}


/**@brief   Function for handling app_uart events.
 *
 * @details This function will receive a single character from the app_uart module and append it to
 *          a string. The string will be be sent over BLE when the last character received was a
 *          'new line' '\n' (hex 0x0A) or if the string has reached the maximum data length.
 */
/**@snippet [Handling the data received over UART] */
uint32_t FIFO_ERR_CODE;

void uart_event_handle(app_uart_evt_t * p_event)
{
    static uint8_t data_array[BLE_NUS_MAX_DATA_LEN];
    static uint8_t index = 0;
    uint32_t       err_code;

    switch (p_event->evt_type)
    {
        case APP_UART_DATA_READY:
            UNUSED_VARIABLE(app_uart_get(&data_array[index]));
            index++;

            if ((data_array[index - 1] == '\n') ||
                (data_array[index - 1] == '\r') ||
                (index >= m_ble_nus_max_data_len))
            {
                if (index > 1)
                {
                    NRF_LOG_DEBUG("Ready to send data over BLE NUS");
                    NRF_LOG_HEXDUMP_DEBUG(data_array, index);

                    do
                    {
                        uint16_t length = (uint16_t)index;
                        err_code = ble_nus_data_send(&m_nus, data_array, &length, m_conn_handle);
                        if ((err_code != NRF_ERROR_INVALID_STATE) &&
                            (err_code != NRF_ERROR_RESOURCES) &&
                            (err_code != NRF_ERROR_NOT_FOUND))
                        {
                            APP_ERROR_CHECK(err_code);
                        }
                    } while (err_code == NRF_ERROR_RESOURCES);
                }

                index = 0;
            }
            break;

        case APP_UART_COMMUNICATION_ERROR:
            APP_ERROR_HANDLER(p_event->data.error_communication);
            break;

        case APP_UART_FIFO_ERROR:
            FIFO_ERR_CODE = p_event->data.error_code;
            APP_ERROR_HANDLER(p_event->data.error_code);
            break;

        default:
            break;
    }
}
/**@snippet [Handling the data received over UART] */


/**@brief  Function for initializing the UART module.
 */
/**@snippet [UART Initialization] */
static void uart_init(void)
{
    uint32_t                     err_code;
    app_uart_comm_params_t const comm_params =
    {
        .rx_pin_no    = RX_PIN_NUMBER,
        .tx_pin_no    = TX_PIN_NUMBER,
        .rts_pin_no   = RTS_PIN_NUMBER,
        .cts_pin_no   = CTS_PIN_NUMBER,
        .flow_control = APP_UART_FLOW_CONTROL_DISABLED,
        .use_parity   = false,
#if defined (UART_PRESENT)
        .baud_rate    = NRF_UART_BAUDRATE_115200
#else
        .baud_rate    = NRF_UARTE_BAUDRATE_115200
#endif
    };

    APP_UART_FIFO_INIT(&comm_params,
                       UART_RX_BUF_SIZE,
                       UART_TX_BUF_SIZE,
                       uart_event_handle,
                       APP_IRQ_PRIORITY_LOWEST,
                       err_code);
    APP_ERROR_CHECK(err_code);
}
/**@snippet [UART Initialization] */


/**@brief Function for initializing the Advertising functionality.
 */
static void advertising_init(void)
{
    uint32_t               err_code;
    ble_advertising_init_t init;

    memset(&init, 0, sizeof(init));

    init.advdata.name_type          = BLE_ADVDATA_FULL_NAME;
    init.advdata.include_appearance = false;
    init.advdata.flags              = BLE_GAP_ADV_FLAGS_LE_ONLY_LIMITED_DISC_MODE;

    init.srdata.uuids_complete.uuid_cnt = sizeof(m_adv_uuids) / sizeof(m_adv_uuids[0]);
    init.srdata.uuids_complete.p_uuids  = m_adv_uuids;

    init.config.ble_adv_fast_enabled  = true;
    init.config.ble_adv_fast_interval = APP_ADV_INTERVAL;
    init.config.ble_adv_fast_timeout  = APP_ADV_DURATION;
    init.evt_handler = on_adv_evt;

    err_code = ble_advertising_init(&m_advertising, &init);
    APP_ERROR_CHECK(err_code);

    ble_advertising_conn_cfg_tag_set(&m_advertising, APP_BLE_CONN_CFG_TAG);
}


/**@brief Function for initializing buttons and leds.
 *
 * @param[out] p_erase_bonds  Will be true if the clear bonding button was pressed to wake the application up.
 */
static void buttons_leds_init(bool * p_erase_bonds)
{
    bsp_event_t startup_event;

    uint32_t err_code = bsp_init(BSP_INIT_LEDS | BSP_INIT_BUTTONS, bsp_event_handler);
    APP_ERROR_CHECK(err_code);

    err_code = bsp_btn_ble_init(NULL, &startup_event);
    APP_ERROR_CHECK(err_code);

    *p_erase_bonds = (startup_event == BSP_EVENT_CLEAR_BONDING_DATA);
}


/**@brief Function for initializing the nrf log module.
 */
static void log_init(void)
{
    ret_code_t err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();
}


/**@brief Function for initializing power management.
 */
static void power_management_init(void)
{
    ret_code_t err_code;
    err_code = nrf_pwr_mgmt_init();
    APP_ERROR_CHECK(err_code);
}


/**@brief Function for handling the idle state (main loop).
 *
 * @details If there is no pending log operation, then sleep until next the next event occurs.
 */
static void idle_state_handle(void)
{
    UNUSED_RETURN_VALUE(NRF_LOG_PROCESS());
    nrf_pwr_mgmt_run();
}


/**@brief Function for starting advertising.
 */
static void advertising_start(void)
{
    uint32_t err_code = ble_advertising_start(&m_advertising, BLE_ADV_MODE_FAST);
    APP_ERROR_CHECK(err_code);
}

/* * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * * * * * * * * PWM Functions * * * * * * * * * * * * */

/* This function sets enable pin for ISFET circuitry HIGH
 */

const int ENABLE_PWM_PIN = 5;       // Connects ISFET conditioning to PWM
const int PWM_OUT_PIN    = 4;       // Delivers PWM siganl

/* This function is called after PWM instance is ready.
 * Function flips ISFET enable signal HIGH, begins SAADC
 * initialization, starts SAADC
 */
void pwm_ready_callback(uint32_t pwm_id)    // PWM callback function
{
    nrf_delay_us(500);              // Delay to ensure appropriate timing between
    enable_isfet_pwm();             // PWM output, ISFET capacitor, etc
    nrf_delay_us(500);              //
    NRF_LOG_INFO("PWM READY\n");

    // Begin SAADC initialization/start
    enable_pH_voltage_reading();
    NRF_LOG_INFO("ENABLED PH VOLTAGE READING\n");
}

/* This function sets enable pin for ISFET circuitry to HIGH
 */
void enable_isfet_pwm(void)
{
    nrf_drv_gpiote_out_config_t config = NRFX_GPIOTE_CONFIG_OUT_SIMPLE(false);
    nrf_drv_gpiote_init();
    nrf_drv_gpiote_out_init(ENABLE_PWM_PIN, &config);
    nrf_drv_gpiote_out_set(ENABLE_PWM_PIN);
    NRF_LOG_INFO("PWM ENABLED\n");
}

/* This function sets enable pin for ISFET circuitry LOW
 */
void disable_isfet_pwm(void)
{
    nrfx_gpiote_uninit();
    NRF_LOG_INFO("PWM DISABLED\n");
}

/* This function initializes and starts pwm instance,
 * with duty cycle of 50% and frequency of 1Mhz.
 * Function calls pwm_ready_callback() after PWM is ready.
 */
void init_and_start_pwm(void)
{

    // Configure 1 channel pwm @ 1Mhz, output on P0.04
    app_pwm_config_t pwm_cfg = APP_PWM_DEFAULT_CONFIG_1CH(1, PWM_OUT_PIN);
    app_pwm_init(&m_isfet_pwm ,&pwm_cfg,pwm_ready_callback);
    app_pwm_enable(&m_isfet_pwm);
    /* Set the duty cycle - keep trying until PWM is ready... */
    while (app_pwm_channel_duty_set(&m_isfet_pwm, 0, 50) == NRF_ERROR_BUSY);
}

/* This function unitializes pwm instance and frees
 * all associated resources
 */
void uninit_pwm(void)
{
    // redundant, but follows design
    app_pwm_uninit(&m_isfet_pwm);
    NRF_LOG_INFO("PWM UNITIALIZED\n");
}

/* * * * * * * * SAADC Configuration * * * * * * * * * *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * */

#define SAMPLES_IN_BUFFER 20
volatile uint8_t state = 1;

static const nrf_drv_timer_t m_timer = NRF_DRV_TIMER_INSTANCE(1);
static nrf_saadc_value_t     m_buffer_pool[2][SAMPLES_IN_BUFFER];
static nrf_ppi_channel_t     m_ppi_channel;
static uint32_t              avg_saadc_val;


void timer_handler(nrf_timer_event_t event_type, void * p_context)
{
    // To Add Later
}



void saadc_sampling_event_init(void)
{
    ret_code_t err_code;

    /* * * * * * * * * * * *
     * MIGHT TAKE OUT FOR PWM MODULE
     * * * * * * * * * * * */
    //err_code = nrf_drv_ppi_init();
    /* * * * * * * * * * */
    APP_ERROR_CHECK(err_code);

    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    timer_cfg.bit_width = NRF_TIMER_BIT_WIDTH_32;
    err_code = nrf_drv_timer_init(&m_timer, &timer_cfg, timer_handler);
    APP_ERROR_CHECK(err_code);

    /* setup m_timer for compare event every 50ms */
    uint32_t ticks = nrf_drv_timer_us_to_ticks(&m_timer, 10);
    nrf_drv_timer_extended_compare(&m_timer,
                                   NRF_TIMER_CC_CHANNEL0,
                                   ticks,
                                   NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
                                   false);
    nrf_drv_timer_enable(&m_timer);

    uint32_t timer_compare_event_addr = nrf_drv_timer_compare_event_address_get(&m_timer,
                                                                                NRF_TIMER_CC_CHANNEL0);
    uint32_t saadc_sample_task_addr   = nrf_drv_saadc_sample_task_get();

    /* setup ppi channel so that timer compare event is triggering sample task in SAADC */
    err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_ppi_channel_assign(m_ppi_channel,
                                          timer_compare_event_addr,
                                          saadc_sample_task_addr);
    APP_ERROR_CHECK(err_code);
    NRF_LOG_INFO("SAADC INIT'd\n");
}


void saadc_sampling_event_enable(void)
{
    ret_code_t err_code = nrf_drv_ppi_channel_enable(m_ppi_channel);

    APP_ERROR_CHECK(err_code);
    NRF_LOG_INFO("SAADC ENABLED\n");
}

/* Function for converting numbers > 9 to byte arrays in ASCII format
 * @params: Averaged value read from SAADC, ptr to byte array
 */
void num_to_byte_arr(uint8_t *data_arr, uint32_t avg_val)
{
    uint8_t dig1, dig2, dig3;
    if(avg_val > 99) {
        dig1 = avg_val % 10;
        dig2 = ((avg_val % 100) - dig1) / 10;
        dig3 = (avg_val - (dig1 + (dig2 * 10))) / 100;
    
        // Convert to ASCII values
        data_arr[0] = dig3 + 48;
        data_arr[1] = dig2 + 48;
        data_arr[2] = dig1 + 48;
    }
    else if(avg_val > 9) {
        dig3 = 0;
        dig1 = avg_val % 10;
        dig2 = ((avg_val % 100) - dig1) / 10;

        // Convert to ASCII values
        data_arr[0] = dig2 + 48;
        data_arr[1] = dig1 + 48;
    }
}

/* This function unitializes and disables SAADC sampling, restarts N minute timer
 */
void disable_pH_voltage_reading(void)
{
    /* * * * * * * * * * * *
     * * MAYBE REMOVE WITH PWM
     * * * * ** * * * * * */
    //nrf_drv_ppi_uninit();
    /* * * * * */
    nrfx_timer_uninit(&m_timer);
    nrfx_ppi_channel_free(m_ppi_channel);
    nrfx_saadc_uninit();
    NRF_LOG_INFO("SAADC unitialized...\n");

    // *** DISABLE ENABLE ***
    disable_isfet_pwm();
    // *** DISABLE PWM ***
    uninit_pwm();

    // Restart timer
    ret_code_t err_code;
    err_code = app_timer_start(m_timer_id, 5000, NULL);
    APP_ERROR_CHECK(err_code);
    nrf_pwr_mgmt_run();

    NRF_LOG_INFO("TIMER RESTARTED\n");
}

void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
    if (p_event->type == NRF_DRV_SAADC_EVT_DONE) 
    {
        NRF_LOG_INFO("SAADC EVENT DONE\n");
        NRF_LOG_FLUSH();
        ret_code_t err_code;
        uint16_t size;
        avg_saadc_val = 0;

        // Byte arrays to store digits, ending with '\n' line feed char
        uint8_t threedig_data[4] = {0, 0, 0, 10};
        uint8_t twodig_data[3]   = {0, 0, 10};
        uint8_t onedig_data[2]   = {0, 10};

        err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);
        APP_ERROR_CHECK(err_code);

        // Sum and average SAADC values
        for (int i = 0; i < SAMPLES_IN_BUFFER; i++)
        {
            avg_saadc_val += p_event->data.done.p_buffer[i];
        }
        avg_saadc_val = avg_saadc_val/SAMPLES_IN_BUFFER;
        NRF_LOG_INFO("SAADC values read and averaged\n");
        NRF_LOG_FLUSH();
         
        // Convert number to appropriate byte array
        if(avg_saadc_val > 99) {
            num_to_byte_arr(threedig_data, avg_saadc_val);
            size = sizeof(threedig_data);
            err_code = ble_nus_data_send(&m_nus, threedig_data, &size, m_conn_handle);
        }
        else if(avg_saadc_val > 9) {
            num_to_byte_arr(twodig_data, avg_saadc_val);
            size = sizeof(twodig_data);
            err_code = ble_nus_data_send(&m_nus, twodig_data, &size, m_conn_handle);
        }
        else {
            onedig_data[0] = (uint8_t)avg_saadc_val + 48;
            size = sizeof(onedig_data);
            err_code = ble_nus_data_send(&m_nus, onedig_data, &size, m_conn_handle);
        }
        //APP_ERROR_CHECK(err_code);
        NRF_LOG_INFO("BLUETOOTH DATA SENT\n");
        NRF_LOG_FLUSH();
        disable_pH_voltage_reading();
        NRF_LOG_INFO("PH VOLTAGE READING DISABLED\n");
        NRF_LOG_FLUSH();
        
        // nrfx_enable timer
    }
}

void saadc_init(void)
{
    ret_code_t err_code;
    nrf_saadc_channel_config_t channel_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);

    err_code = nrf_drv_saadc_init(NULL, saadc_callback);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_channel_init(0, &channel_config);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);

}

/* * * * * * * End SAADC Configuration * * * * * * * * * 
 * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/* * * * * * * BLE DATA Configuration * * * * * * * * * * 
 * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/* This function initializes and enables SAADC sampling
 */
void enable_pH_voltage_reading(void)
{
    NRF_LOG_INFO("PH VOLTAGE ENABLE STARTED\n");
    saadc_init();
    NRF_LOG_INFO("SAADC INIT\n");
    NRF_LOG_FLUSH();
    saadc_sampling_event_init();
    NRF_LOG_INFO("SAMPLING EVENT INIT\n");
    NRF_LOG_FLUSH();
    saadc_sampling_event_enable();
    NRF_LOG_INFO("SAADC ENABLED\n");
    NRF_LOG_FLUSH();
    nrf_pwr_mgmt_run();
}

void single_shot_timer_handler()
{
    // disable timer
    ret_code_t err_code;
    err_code = app_timer_stop(m_timer_id);
    NRF_LOG_INFO("TIMER HANDLER STARTED\n");

    // Init PWM module, calls pwm_ready callback to enable SAADC
    init_and_start_pwm();

    /* removed, placed in pwm ready callback
     *
     * enable_pH_voltage_reading();
     * NRF_LOG_INFO("ENABLED PH VOLTAGE READING\n");
     */
}

/**@brief Function for handling events from the GATT library. */
void gatt_evt_handler(nrf_ble_gatt_t * p_gatt, nrf_ble_gatt_evt_t const * p_evt)
{
    if ((m_conn_handle == p_evt->conn_handle) && (p_evt->evt_id == NRF_BLE_GATT_EVT_ATT_MTU_UPDATED))
    {
        m_ble_nus_max_data_len = p_evt->params.att_mtu_effective - OPCODE_LENGTH - HANDLE_LENGTH;

        ret_code_t err_code;

         // Create application timer

        err_code = app_timer_create(&m_timer_id,
                                    APP_TIMER_MODE_SINGLE_SHOT,
                                    single_shot_timer_handler);
        APP_ERROR_CHECK(err_code);
        
        // 1 second timer intervals
        err_code = app_timer_start(m_timer_id, APP_TIMER_TICKS(1000), NULL);
        APP_ERROR_CHECK(err_code);

        NRF_LOG_INFO("TIMER STARTED\n");
        NRF_LOG_FLUSH();

        nrf_pwr_mgmt_run();
    }
    NRF_LOG_DEBUG("ATT MTU exchange completed. central 0x%x peripheral 0x%x",
                  p_gatt->att_mtu_desired_central,
                  p_gatt->att_mtu_desired_periph);
}

/**@brief Function for initializing the GATT library. */
void gatt_init(void)
{
    ret_code_t err_code;

    err_code = nrf_ble_gatt_init(&m_gatt, gatt_evt_handler);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_ble_gatt_att_mtu_periph_set(&m_gatt, NRF_SDH_BLE_GATT_MAX_MTU_SIZE);
    APP_ERROR_CHECK(err_code);
}

/* * * * * * * END DATA Configuration * * * * * * * * * * 
 * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/**@brief Application main function.
 */
int main(void)
{
    bool erase_bonds;

    // Run heartbeat startup
    run_heartbeat();
    // Initialize

    
    uart_init();
    log_init();
    timers_init();
    buttons_leds_init(&erase_bonds);
    power_management_init();
    ble_stack_init();
    gap_params_init();
    gatt_init();
    services_init();
    advertising_init();
    conn_params_init();
    NRF_LOG_FLUSH();

    // Start execution    
    advertising_start();

    // Enter main loop.
    for (;;)
    {
        idle_state_handle();
    }
    
}


/**
 * @}
 */

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