How to read two analog inputs using SAADC?

Question

I have developed an application that reads data from an analog sensor and transmits data with UART. This app is based off the SDK v14.x uart example, and SAADC example. While my application works fine for reading one analog input, I now need to read data from two different analog inputs and transmit their data in the same bluetooth packet.

The initialization call I use for the SAADC is

NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN1);

* followed by *

nrf_drv_saadc_init(NULL, saadc_callback);

and other relevant code (attached to this question below). With these functions, I can only specify one analog input and one callback function. I want to use two analog pins, and I also want my saadc_callback behavior to be different for each "done" event. I essentially want to read analog_input_1, then immediately afterwards read analog_input_2 (no/minimal delay between readings), and once both inputs are read I want to transmit a packet via BLE. Once I can read from two different pins, how can I create different different callback behaviors (I.E. store data from analog_input_1 until analog_input_2 is read, then send after input_2 is read)? I could potentially use a global boolean/counter and datastructure to store information from analog_input_1 until it's ready, then simply use an if statement within my callback, but there certainly has to be a more elegant solution.

I also use a timer event to read from the SAADC, and will need to make sure I can take both readings using the same timer still.

Code is attached. Relevant functions I need to edit to support multiple analog pins and callback behavior are saadc_sampling_event_init, saadc_sampling_event_enable, saadc_callback, and saadc_init. Any help would be greatly appreciated!

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/**
 * 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.
 *
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

/**
 * 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.
 *
 */

/** UCHU Biosensors, Inc.
 *
 * This application has been extended from the orginal Nordic UART example,
 * provided within SDK V14. This application has been developed by Noah Hill
 * and UCHU Biosensors, Inc. to be deployed on an nRF52810.
 *
 */

/** @file
 *
 * @brief    Reads analog pin using PWM and SAADC, transmits data using UART
 *           over BLE, sleeps for x minutes (repeat).
 *
 * 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,
 * the PWM module, the SAADC module, and the application timer peripheral.
 *
 * Application set to be ran using internal 32KHz RC oscillator.
 *
 */


#include <stdint.h>
#include <string.h>
#include "nordic_common.h"

#include "app_uart.h"
#include "app_util_platform.h"
#include "app_fifo.h"
#include "app_error.h"
#include "app_timer.h"
#include "app_pwm.h"

#include "ble_hci.h"
#include "ble_advdata.h"
#include "ble_advertising.h"
#include "ble_conn_params.h"
#include "ble_nus.h"

#include "nrf.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 "nrf_drv_clock.h"
#include "nrf_drv_gpiote.h"
#include "nrf_drv_saadc.h"
#include "nrf_drv_ppi.h"
#include "nrf_drv_timer.h"
#include "nrf_delay.h"
#include "nrf_pwr_mgmt.h"
#include "nrf_saadc.h"

#include "nrfx_ppi.h"
#include "nrfx_pwm.h"
#include "nrfx_saadc.h"

#include "bsp_btn_ble.h"
#include "boards.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

#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 "PWM2" using TIMER2.

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}
};

// UCHU nRF52810 port assignments 
#define NUM_UNUSED_PINS   13
#define HEARTBEAT_PIN     15
#define PH_INPUT          3
#define TEMP_A            5 
#define ENABLE_PWM_PIN    8
#define REED_SWITCH       16
#define PWM_OUT_PIN       20
#define BTN_PRESSED       0 

// 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);
void enable_switch              (void);
void check_reed_switch          (void);


/**@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 sendit 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).
    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);

            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;
            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);
            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);
            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] */
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;

        /* * * * REMOVED ERROR HANDLERS DUE TO NORDIC BUG "NO MEM" * * * */
        /*	   *	  *		 *		*	  *		 *	    *	   *     *   */

        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 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);
    if(nrf_drv_gpiote_is_init() == 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;

    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 timer compare event triggers 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)
{
    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);
        }

        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();
    }
}

/* Reads pH transducer output with GPIO 3 (AIN1)
 */
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_AIN1);

    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();
}

/**@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);
        
        // N 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 * * * * * * * * * */ 


/* * * * * * * * HEARTBEAT FUNCTIONS * * * * * * * * * * *
 *
 * For debugging purposes only.
 *
 * Flashes on-board LED (UCHU RF Board R1)
 * two times upon main entry.
 *
 * * * * * * * * HEARTBEAT FUNCTIONS * * * * * * * * * * */

/* This function sets enable pin for ISFET circuitry to HIGH
 */
void led_on(void)
{
      if(nrf_drv_gpiote_is_init() == false) {
            nrf_drv_gpiote_init();
      }
      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_toggle(HEARTBEAT_PIN);
}

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

void run_heartbeat(void)
{
    uint8_t err_code;
    NRF_LOG_INFO("POWERED ON\n");
    NRF_LOG_FLUSH();
    if(nrf_drv_gpiote_is_init() == false) {
          err_code = nrf_drv_gpiote_init();
          APP_ERROR_CHECK(err_code);
    }
    for(int i = 0; i < 2; i++) {
      NRF_LOG_INFO("toggling led\n");
      NRF_LOG_FLUSH();
      nrf_delay_ms(100);
      led_on();
      nrf_delay_ms(100);
      led_off();
    }
    nrf_drv_gpiote_out_clear(HEARTBEAT_PIN);
}

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

/* Peripheral debugging functions */
void enable_switch(void)
{
    if(nrf_drv_gpiote_is_init() == false) {
          nrf_drv_gpiote_init();
    }
    // Set reed switch as pulldown input
    nrf_gpio_cfg_input(REED_SWITCH, NRF_GPIO_PIN_PULLDOWN);
    NRF_GPIO->PIN_CNF[REED_SWITCH] 
    					= (GPIO_PIN_CNF_SENSE_Low << GPIO_PIN_CNF_SENSE_Pos)
                        | (GPIO_PIN_CNF_DRIVE_S0S1 << GPIO_PIN_CNF_DRIVE_Pos)
                        | (GPIO_PIN_CNF_PULL_Disabled << GPIO_PIN_CNF_PULL_Pos)
                        | (GPIO_PIN_CNF_INPUT_Connect << GPIO_PIN_CNF_INPUT_Pos)
                        | (GPIO_PIN_CNF_DIR_Input << GPIO_PIN_CNF_DIR_Pos);
}

void check_reed_switch(void)
{
      if(nrf_drv_gpiote_is_init() == false) {
            nrf_drv_gpiote_init();
      }
      if(nrf_gpio_pin_read(REED_SWITCH) == BTN_PRESSED){
          led_on();
          nrf_delay_ms(200);
          led_off();
          nrf_delay_ms(1000);
          NRF_LOG_INFO("POWERING OFF...\n");
          NRF_LOG_FLUSH();
          // Enter system OFF. After wakeup the chip will be reset.
          NRF_POWER->SYSTEMOFF = 1;
      }  
}

/**@brief Application main function.
 */
int main(void)
{
    bool erase_bonds;
    // Initialize
    uart_init();
    log_init();
    run_heartbeat();
    enable_switch();
    timers_init();

    /* * * TO DO: takeout board buttons * * *
        buttons_leds_init(&erase_bonds);
      * * * * * * * * * * * * * * * * * * */

    power_management_init();
    ble_stack_init();
    gap_params_init();
    gatt_init();
    services_init();
    advertising_init();
    conn_params_init();

    // Start execution, enable reset switch
    advertising_start();

    // Enter main loop.
    while (true)
    {
        check_reed_switch();
        idle_state_handle();
    } 
}

/**
 * @}
 */

Jørgen Holmefjord · Accepted Answer

Hi, 
 The SAADC peripheral will by default store samples directly in a buffer in RAM. I would recommend that you use scan mode (enabled automatically when more than one channel is enabled) with a buffer size of 2, and trigger a single sample to sample both channels. This will sample the channels successively with minimal delay, and you will get a done event once both channels have been samples. The callback will give a pointer to the buffer where the samples are stored. 
 You can easily add more channels to the SAADC example in the SD K by adding these lines in saadc_init(): 
 nrf_saadc_channel_config_t channel_config2 =
 NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN1);

err_code = nrf_drv_saadc_channel_init(1, &channel_config);
APP_ERROR_CHECK(err_code); 
 Best regards, Jørgen

paul · Answer

Hi, 
 there are no doubt many ways to do this. In the following I am reading battery voltage and the presence of metal with a hall effect sensor. 
 #define HALL_PIN NRF_SAADC_INPUT_AIN0 /// analog pin 0
#define VOLT_PIN NRF_SAADC_INPUT_AIN2 /// analog pin 2
#define VOLT_CHANNEL 0 /// SAADC channel no
#define HALL_CHANNEL 1 /// SAADC channel no

static nrf_saadc_channel_config_t ch_config_volts = 
 NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(VOLT_PIN);
static nrf_saadc_channel_config_t ch_config_hall = 
 NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(HALL_PIN);
static nrf_saadc_value_t adc_buf[2]; //!< Buffer used for storing ADC value.
static nrf_saadc_value_t volts_raw, hall_raw;

void saadc_init(void)
{ 
 uint32_t err_code;
 nrfx_saadc_config_t saadc_config = NRFX_SAADC_DEFAULT_CONFIG;
 
 // Fine tune saadc params
 ch_config_volts.gain = NRF_SAADC_GAIN1_4;
 /// gain of a half produced range of ~0x75 compared to ~0x35 for quarter
 ch_config_hall.gain = NRF_SAADC_GAIN1_2;

 // init the adc
 err_code = nrfx_saadc_init(&saadc_config, saadc_event_handler);
 // no point testing error.it is either success or complaining that it has been initialised

 // do a calibrate
 while (nrfx_saadc_calibrate_offset() != NRFX_SUCCESS)
 nrf_delay_ms(10);
 while (nrfx_saadc_is_busy())
 nrf_delay_ms(10);
 
 // config the adc channel to read cpu internal volts 
 err_code = nrfx_saadc_channel_init(VOLT_CHANNEL, &ch_config_volts); 
 APP_ERROR_CHECK(err_code);

 // config the adc channel to read hall sensor 
 err_code = nrf_drv_saadc_channel_init(HALL_CHANNEL, &ch_config_hall); 
 APP_ERROR_CHECK(err_code);

 err_code = nrfx_saadc_buffer_convert(adc_buf, sizeof(adc_buf)/sizeof(nrf_saadc_value_t));
 APP_ERROR_CHECK(err_code);

 nrfx_saadc_sample();
}

/** @brief Function handling events from 'nrf_drv_saadc.c'.
 *
 * @param[in] p_evt SAADC event.
 */
static void saadc_event_handler(nrf_drv_saadc_evt_t const * p_evt)
{
 if (p_evt->type == NRFX_SAADC_EVT_DONE)
 {
 // just need to copy values now because could be overwritten at any time
 volts_raw = p_evt->data.done.p_buffer[VOLT_CHANNEL];
 hall_raw = p_evt->data.done.p_buffer[HALL_CHANNEL];
 } else if (p_evt->type == NRFX_SAADC_EVT_CALIBRATEDONE) {
 // don't do anything - we call calibrate every now and then and this comes back
 } else if (p_evt->type == NRFX_SAADC_EVT_LIMIT) {
 // not setting any limits with nrfx_saadc_limits_set so should never fire
 }
}

/**
** @brief wrapper for saadc_get that returns the last voltage reading
** @param[out] p_vbatt returns the last voltage reading
**
*/
void saadc_get_volts(uint16_t * p_vbatt) {
 
 // convert and return the current volts
 *p_vbatt = ADC_RESULT_IN_MILLI_VOLTS(volts_raw);

 // schedule another go
 saadc_get();
}

/**
** @brief wrapper for saadc_get that returns the last hall effect reading
** @param[out] p_lvl_hall returns the last voltage reading
**
*/
void saadc_get_hall(uint16_t * p_lvl_hall) {
 
 // convert and return the hall value
 *p_lvl_hall = hall_raw;

 // schedule another go
 saadc_get();
}

/**
** @brief kick off the adc. value comes back in evt handler
** 
*/
static void saadc_get(void)
{
 ret_code_t err_code;

 // does the read which takes time 
 // value returned through the event handler
 if (!nrfx_saadc_is_busy())
 {
 err_code = nrfx_saadc_buffer_convert(adc_buf, sizeof(adc_buf)/sizeof(nrf_saadc_value_t));
 APP_ERROR_CHECK(err_code);

 nrfx_saadc_sample();
 }
}

 
 I have no idea why I used two different calls to do the channel init - guess I was having a bad day at the time. They should probably both be the nrfx versions since they are the latest and greatest. 
 Cheers Paul

How to read two analog inputs using SAADC?

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