current consumption for ble nrf52840

[NANDANI]

I’m writing BLE UART code.
When BLE is not connected, current consumption is ~30 µA.
But when BLE is connected, consumption increases by ~1 mA.
I want to reduce the current during an active BLE connection—ideally back toward the disconnected level.
Is that theoretically possible? What suggestions do you have?

#include <stdio.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_drv_saadc.h"
#include "app_error.h"
//#include "nrf_delay.h"
#include "nrf_drv_ppi.h"
#include "nrf_drv_timer.h"
#include "nrf_gpio.h"
#include "nrfx_rtc.h"
#include "nrf_drv_clock.h"


#include "nrf_drv_rtc.h"
#include "nrf_soc.h"
#include "nrf_nvic.h"
#include "app_error.h"
#include "app_util_platform.h"
#include "nrf_pwr_mgmt.h"

#include "app_error.h"
#include "nrf_drv_clock.h"
#include "nrf_nvmc.h"


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

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


//#define ADC_UPDATE_INTERVAL_MIN 1 // ADC update interval in minutes
//#define TICK_INTERVAL_MS 125
//#define TOTAL_TICKS ((ADC_UPDATE_INTERVAL_MIN * 60000) / TICK_INTERVAL_MS) 
//const nrfx_rtc_t rtc = NRFX_RTC_INSTANCE(2);
//volatile uint32_t tick_count = 0;  // Tick counter
//nrf_saadc_value_t adc_val;
//nrf_saadc_value_t adc_save[360];  // Array to store ADC samples
//uint16_t i = 0; 


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

#define DEVICE_NAME                     "MAyur_Nordic"                               /**< 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                1600//64                                          /**< The advertising interval (in units of 0.625 ms. This value corresponds to 40 ms). */

#define APP_ADV_DURATION                6000//18000                                       /**< The advertising duration (180 seconds) in units of 10 milliseconds. */

#define MIN_CONN_INTERVAL               MSEC_TO_UNITS(300, UNIT_1_25_MS) //100  //200            /**< Minimum acceptable connection interval (20 ms), Connection interval uses 1.25 ms units. */
#define MAX_CONN_INTERVAL               MSEC_TO_UNITS(400, UNIT_1_25_MS)  //200  //400           /**< Maximum acceptable connection interval (75 ms), Connection interval uses 1.25 ms units. */
#define SLAVE_LATENCY                   2//4//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. */



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}
};

void assert_nrf_callback(uint16_t line_num, const uint8_t * p_file_name);
static void timers_init(void);
static void gap_params_init(void);
static void nrf_qwr_error_handler(uint32_t nrf_error);
static void nus_data_handler(ble_nus_evt_t * p_evt);
static void services_init(void);
static void on_conn_params_evt(ble_conn_params_evt_t * p_evt);

static void conn_params_error_handler(uint32_t nrf_error);
static void conn_params_init(void);
static void on_adv_evt(ble_adv_evt_t ble_adv_evt);
static void ble_evt_handler(ble_evt_t const * p_ble_evt, void * p_context);
static void ble_stack_init(void);
void gatt_evt_handler(nrf_ble_gatt_t * p_gatt, nrf_ble_gatt_evt_t const * p_evt);
void gatt_init(void);
void uart_event_handle(app_uart_evt_t * p_event);
static void uart_init(void);
static void advertising_init(void);
static void log_init(void);
static void advertising_start(void);

void idle_state_handle()
{
          __WFE();   // Wait for event (low-power)
          __SEV();   // Set event (in case event missed)
          __WFE();   // Wait again to enter sleep
}

void uart_disable(void)
{
    app_uart_close();  // Closes UART FIFO and disables interrupts
}

int main(void)
{   

  // NRF_POWER->DCDCEN = 1;  // Enable DC/DC converter
  
    timers_init();
    ble_stack_init();   // ble work that time nvmc is not work. for data save. 
    gap_params_init();
    gatt_init();
    services_init();
    advertising_init();
    conn_params_init();
    advertising_start();
    printf("application start");
    for (;;)
    {
     idle_state_handle();
    }
}



void assert_nrf_callback(uint16_t line_num, const uint8_t * p_file_name)
{
    app_error_handler(DEAD_BEEF, line_num, p_file_name);
}

static void timers_init(void)
{
    ret_code_t err_code = app_timer_init();
    APP_ERROR_CHECK(err_code);
}

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);
}

static void nrf_qwr_error_handler(uint32_t nrf_error)
{
    APP_ERROR_HANDLER(nrf_error);
}

//static void nus_data_handler(ble_nus_evt_t * p_evt)
//{
//	// A variable to hold the error code FOR THE 

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

//        uint8_t data[200]; 
        
//       // 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);
//        }
//    }

//}


static void nus_data_handler(ble_nus_evt_t * p_evt)
{
    if (p_evt->type == BLE_NUS_EVT_RX_DATA)
    {
        uint8_t data[200];
        uint8_t data1[20];

        // Copy received data and null-terminate
        memcpy(data, p_evt->params.rx_data.p_data, p_evt->params.rx_data.length);
        data[p_evt->params.rx_data.length] = '\0';

        // ✅ Print received data over BLE
        printf("Received over BLE: %s\n", data);

        sprintf((char *)data1, "ADC: %s", data);

        uint16_t length = strlen((char *)data1);
        uint32_t err_code = ble_nus_data_send(&m_nus, data, &length, m_conn_handle);

         if (err_code == NRF_SUCCESS)
        {
            printf("Sent over BLE: %s\n", data1); // Print confirmation on SES Terminal
        }
        else
        {
            printf("BLE Send Error: %d\n", err_code);
        }

        // ✅ Optional: Echo back to UART (if needed)
        for (uint32_t i = 0; i < p_evt->params.rx_data.length; i++)
        {
            while (app_uart_put(p_evt->params.rx_data.p_data[i]) == NRF_ERROR_BUSY);
        }

        // Add newline if '\r' was last character
        if (p_evt->params.rx_data.p_data[p_evt->params.rx_data.length - 1] == '\r')
        {
            while (app_uart_put('\n') == NRF_ERROR_BUSY);
        }
    }
}

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);
}

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);
    }
}

static void conn_params_error_handler(uint32_t nrf_error)
{
    APP_ERROR_HANDLER(nrf_error);
}

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);
}



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:
        idle_state_handle();
            break;
        case BLE_ADV_EVT_IDLE:
           // sleep_mode_enter();
           //sd_power_system_off();
           advertising_start();  // Restart advertising
            break;
        default:
            break;
    }
}

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:
           // NRF_LOG_INFO("Connected")
            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);
            uart_init();
             break;

        case BLE_GAP_EVT_DISCONNECTED:
            //NRF_LOG_INFO("Disconnected");
            // LED indication will be changed when advertising starts.
            m_conn_handle = BLE_CONN_HANDLE_INVALID;
            uart_disable();
            //sd_power_system_off();  // Power down
           idle_state_handle();
                      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;
    }
}


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);
}

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;
      //  NRF_LOG_INFO("Data len is set to 0x%X(%d)", m_ble_nus_max_data_len, m_ble_nus_max_data_len);
    }
    //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);
}

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);
}



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:
            APP_ERROR_HANDLER(p_event->data.error_code);
            break;

        default:
            break;
    }
}



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);


    NRF_P0->PIN_CNF[RX_PIN_NUMBER] |= GPIO_PIN_CNF_PULL_Msk;
}
/**@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 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);
}

[Tubald]

Hello,
Sorry for not knowing the answer to your question, but maybe you can help me answer mine.
How do you measure the current consumption? I am trying to do this on my nrf52840 with a multimeter, but without any success.

I would really appreciate if you could tell me how to do it. 

Thank you

[NANDANI]

power profiler kit using measure current consumption.

[Edvin]

Hello,

Tubald said:

How do you measure the current consumption? I am trying to do this on my nrf52840 with a multimeter, but without any success.

The challenge is that a BLE device will have very little current consumption most of the time, but then it will have large spikes, when the radio is being used, and for some periods where the CPU is being used. Most Multimeters may not sample quick enough to see these spikes, so it will give a very inaccurate measurement. 

As NANDANI  says, you can use the Power Profiler Kit (II) to measure an accurate current consumption, either on our DKs, or 3rd party devices. It is actually a very good tool for it's price. You can also use it as a logic analyzer for signals that aren't too fast. 

Regarding your current consumption:

When BLE is not connected, current consumption is ~30 µA.
But when BLE is connected, consumption increases by ~1 mA.

From what I can tell from your main.c file, you are using an advertising interval of 1000ms, and a connection interval between 300ms and 400ms. The 300 and 400ms, however, is a desired connection interval. It is not guaranteed that you will actually achieve this. It depends on your central device, who has the final saying in connection parameters.

What you can do is to try to connect to your peripheral using nRF Connect for Desktop, and it's "Bluetooth Low Energy" app. It does require an extra DK, but it will accept any connection parameter change request that the peripheral requests. So when the central first connects, it will decide the connection interval. But after FIRST_CONN_PARAMS_UPDATE_DELAY (5 seconds in your case) the peripheral will request it's desired connection parameters, given it is outside your desired parameters (300ms and 400ms). 

Do you see that the current consumption goes down after 5 seconds? What if you use the nRF Connect for Desktop -> Bluetooth Low Energy app? 

If not, can you try adding this to your ble_evt_handler():

        case BLE_GAP_EVT_CONN_PARAM_UPDATE:
            uint16_t max_conn_int = p_ble_evt->evt.gap_evt.params.conn_param_update.conn_params.max_conn_interval;
            uint16_t min_conn_int = p_ble_evt->evt.gap_evt.params.conn_param_update.conn_params.min_conn_interval;
            NRF_LOG_INFO("connection parameters updated. max: %d, min: %d", max_conn_int, min_conn_int);
            break;
        case BLE_GAP_EVT_CONN_PARAM_UPDATE_REQUEST:
            uint16_t max_conn_int = p_ble_evt->evt.gap_evt.params.conn_param_update_request.conn_params.max_conn_interval;
            uint16_t min_conn_int = p_ble_evt->evt.gap_evt.params.conn_param_update_request.conn_params.min_conn_interval;
            NRF_LOG_INFO("Connection parameters update request. max: %d, min: %d", max_conn_int, min_conn_int);
            break;

You can also add this to the BLE_GAP_EVT_CONNECTED case:

        case BLE_GAP_EVT_CONNECTED:
            NRF_LOG_INFO("Connected");
            [...]
            uint16_t max_conn_int = p_ble_evt->evt.gap_evt.params.connected.conn_params.max_conn_interval;
            uint16_t min_conn_int = p_ble_evt->evt.gap_evt.params.connected.conn_params.min_conn_interval;
            NRF_LOG_INFO("connection parameters: max: %d, min: %d", max_conn_int, min_conn_int);
            break;

To see your initial connection parameters. 

What do you see? Does the connection parameters update after the connection event? 

Best regards,

Edvin