Scanning cannot find Public MAC

[jfarjona]

Hello:

I have set the scanning module to search devices by MAC address.  It finds the devices that are using a Static Random address, but it cannot find the ones using a Public Static address.

I can see and connect to both using NRF Connect BLE.  I am using the Rigardo module.

Here is the code I use to start the scanning module:

ret_code_t connect_to_mac(uint8_t mac[]) {
  ret_code_t err_code;
  if (isConnected()) {
    uint8_t mac[6];
    getCurrentMac(mac);
    disconnect_from_mac(mac);
  }
  nrf_ble_scan_stop();
  nrf_ble_scan_all_filter_remove(&m_scan);

  nrf_ble_scan_init_t init_scan;

  ble_gap_addr_t m_mac_filter;
  m_mac_filter.addr_type = BLE_GAP_ADDR_TYPE_PUBLIC;
  err_code = nrf_ble_scan_copy_addr_to_sd_gap_addr(&m_mac_filter, mac);

  if (err_code == NRF_SUCCESS) {
    memset(&init_scan, 0, sizeof(init_scan));

    init_scan.connect_if_match = true;
    init_scan.conn_cfg_tag = APP_BLE_CONN_CFG_TAG;
    m_mac_filter.addr_type = BLE_GAP_ADDR_TYPE_PUBLIC;
    err_code = nrf_ble_scan_init(&m_scan, &init_scan, scan_evt_handler);
    if (err_code == NRF_SUCCESS) {
      err_code = nrf_ble_scan_filter_set(&m_scan, SCAN_ADDR_FILTER, &m_mac_filter.addr);
    }
    if (err_code == NRF_SUCCESS) {
      err_code = nrf_ble_scan_filters_enable(&m_scan, NRF_BLE_SCAN_ADDR_FILTER, false);
    }
    if (err_code == NRF_SUCCESS) {
      err_code = scan_start();
      if (err_code == NRF_SUCCESS) {
#ifdef DEBUG
        char *msg = malloc(255);
        sprintf(msg, "SCANNING FOR %x:%x:%x:%x:%x:%x TYPE %d",
            m_mac_filter.addr[0],
            m_mac_filter.addr[1],
            m_mac_filter.addr[2],
            m_mac_filter.addr[3],
            m_mac_filter.addr[4],
            m_mac_filter.addr[5],
            m_mac_filter.addr_type);
        err_code = sendStatusToUART(msg);
        free(msg);
#else
        err_code = sendStatusToUART(STATUS_SCANNING);
#endif
      }
    }
    BLE_ERROR_CHECK(err_code);
  } else {
    sendErrorToUART(ERROR_INVALID_MAC);
  }

  return err_code;
}

Can you please point me to any ideas?  The only difference between the two devices is that one MAC is public (using Rigardo defined hardware address) and the other is Random Static.

Are there any limitations on the softdevice for hardware public address?

Thanks,

Juan

[jfarjona]

I have followed the comments from Kenneth (https://devzone.nordicsemi.com/f/nordic-q-a/44653/scan-address-filter-not-matching-addr_type-public-vs-random_static). 

    case BLE_GAP_EVT_ADV_REPORT: {
      char* msg = malloc(256);
      memset(msg,0,256);
      sprintf(msg, "FOUND ADDRESS %x:%x:%x:%x:%x:%x TYPE %d RESPONSE %d",
          p_ble_evt->evt.gap_evt.params.adv_report.peer_addr.addr[0],
          p_ble_evt->evt.gap_evt.params.adv_report.peer_addr.addr[1],
          p_ble_evt->evt.gap_evt.params.adv_report.peer_addr.addr[2],
          p_ble_evt->evt.gap_evt.params.adv_report.peer_addr.addr[3],
          p_ble_evt->evt.gap_evt.params.adv_report.peer_addr.addr[4],
          p_ble_evt->evt.gap_evt.params.adv_report.peer_addr.addr[5],
          p_ble_evt->evt.gap_evt.params.adv_report.peer_addr.addr_type,
          p_ble_evt->evt.gap_evt.params.adv_report.type.scan_response);
      sendStatusToUART(msg);
      free(msg);
      break;
    }
    

The report shows:

FOUND ADDRESS 25:9a:5c:93:54:94 TYPE 0 RESPONSE 1

Which shows me that it should be matched (that's the sought mac)... any ideas?  

Thanks,

Juan

[jfarjona]

And now I am retrieving the filters after I start scanning, and here is what I see the problem happening.

 [ ... ]
 
    err_code = scan_start();
      if (err_code == NRF_SUCCESS) {
        char *msg = malloc(255);
        memset(msg, 0, 255);
        sprintf(msg, "SCANNING FOR %x:%x:%x:%x:%x:%x TYPE %d",
            m_mac_filter.addr[0],
            m_mac_filter.addr[1],
            m_mac_filter.addr[2],
            m_mac_filter.addr[3],
            m_mac_filter.addr[4],
            m_mac_filter.addr[5],
            m_mac_filter.addr_type);
        err_code = sendStatusToUART(msg);
        nrf_ble_scan_filters_t filters;
        memset(&filters, 0, sizeof(nrf_ble_scan_filters_t));
        memset(msg, 0, 255);
        nrf_ble_scan_filter_get( &m_scan, &filters);
        sprintf(msg, "FILTERS: COUNT=%d ENABLED=%d ADDRESS=%x:%x:%x:%x:%x:%x TYPE=%d",
            filters.addr_filter.addr_cnt,
            filters.addr_filter.addr_filter_enabled,
            filters.addr_filter.target_addr[0].addr[0],
            filters.addr_filter.target_addr[0].addr[1],
            filters.addr_filter.target_addr[0].addr[2],
            filters.addr_filter.target_addr[0].addr[3],
            filters.addr_filter.target_addr[0].addr[4],
            filters.addr_filter.target_addr[0].addr[5],
            filters.addr_filter.target_addr[0].addr_type);
        err_code = sendStatusToUART(msg);
        free(msg);
    }
    

And I am getting the following:

SCANNING FOR 25:9a:5c:93:54:94 TYPE 0

FILTERS: COUNT=1 ENABLED=1 ADDRESS=25:9a:5c:93:54:94 TYPE=2

For some reason, the scanning module is replacing the address type to

BLE_GAP_ADDR_TYPE_RANDOM_PRIVATE_RESOLVABLE

When the address is of type BLE_GAP_ADDR_TYPE_PUBLIC.

Now, looking at the code on the SDK, the function that determines the type of address is

nrf_ble_scan_address_type_decode

And it checks if it is public by the code:

 // See Bluetooth Core Specification Vol 6, Part B, section 1.3.
    addr_type  = addr_type >> 6;
    addr_type &= 0x03;

In my case, the first byte is 94, which 96 >> 6 is 1, so it resolves as Public.  But once the scanning starts, it gets resolved otherwise.

Does anyone know how can I fix this?  Is this a bug in the SDK ?  (I am using version 16, softdevice 7.0.1 for s104)

Thanks,

Juan

[jfarjona]

So for those who may be under the same fight... I hacked the code by:

 if (err_code == NRF_SUCCESS) {
      err_code = nrf_ble_scan_filter_set(&m_scan, SCAN_ADDR_FILTER, &m_mac_filter.addr);
    }
    if (err_code == NRF_SUCCESS) {
      // hack this:
      m_scan.scan_filters.addr_filter.target_addr[0].addr_type = BLE_GAP_ADDR_TYPE_PUBLIC;
      err_code = nrf_ble_scan_filters_enable(&m_scan, NRF_BLE_SCAN_ADDR_FILTER, false);
    }

And it all works.  Far from ideal, but solves my problem.

If anyone knows a non-hacked solution, please let me know.

Juan

[Simon]

I am happy you found a solution and thanks for sharing it. I've not had time to figure out a non-hacked solution to your problem, but let's go with your solution temporary. If you encounter any problems with this solution, please tell me and I will look into it.

Best regards,

Simon

[jfarjona]

Thanks.  This will work for us for now.  But is not a sustainable solution, as we will have to find out if the address is public or private on our own, instead of using the SDK; or do all sort of IF statements to make sure the filter is set properly.

Cheers,

Juan

[Simon]

This might be a bug. I will talk to the developers and try to get to the bottom of it.

Best regards,

Simon

[Simon]

What SDK are you using? I was not able to recreate your issue in SDK 16. Could you copy SDK16/examples/ble_central into a new folder and copy the following into main.c:

/**
 * Copyright (c) 2016 - 2019, Nordic Semiconductor ASA
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form, except as embedded into a Nordic
 *    Semiconductor ASA integrated circuit in a product or a software update for
 *    such product, must reproduce the above copyright notice, this list of
 *    conditions and the following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 *
 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
 *
 * 5. Any software provided in binary form under this license must not be reverse
 *    engineered, decompiled, modified and/or disassembled.
 *
 * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY, NONINFRINGEMENT, AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL NORDIC SEMICONDUCTOR ASA OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */
#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>
#include "nordic_common.h"
#include "app_error.h"
#include "app_uart.h"
#include "ble_db_discovery.h"
#include "app_timer.h"
#include "app_util.h"
#include "bsp_btn_ble.h"
#include "ble.h"
#include "ble_gap.h"
#include "ble_hci.h"
#include "nrf_sdh.h"
#include "nrf_sdh_ble.h"
#include "nrf_sdh_soc.h"
#include "ble_nus_c.h"
#include "nrf_ble_gatt.h"
#include "nrf_pwr_mgmt.h"
#include "nrf_ble_scan.h"

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


#define APP_BLE_CONN_CFG_TAG    1                                       /**< Tag that refers to the BLE stack configuration set with @ref sd_ble_cfg_set. The default tag is @ref BLE_CONN_CFG_TAG_DEFAULT. */
#define APP_BLE_OBSERVER_PRIO   3                                       /**< BLE observer priority of the application. There is no need to modify this value. */

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

#define NUS_SERVICE_UUID_TYPE   BLE_UUID_TYPE_VENDOR_BEGIN              /**< UUID type for the Nordic UART Service (vendor specific). */

#define ECHOBACK_BLE_UART_DATA  1                                       /**< Echo the UART data that is received over the Nordic UART Service (NUS) back to the sender. */


BLE_NUS_C_DEF(m_ble_nus_c);                                             /**< BLE Nordic UART Service (NUS) client instance. */
NRF_BLE_GATT_DEF(m_gatt);                                               /**< GATT module instance. */
BLE_DB_DISCOVERY_DEF(m_db_disc);                                        /**< Database discovery module instance. */
NRF_BLE_SCAN_DEF(m_scan);                                               /**< Scanning Module instance. */
NRF_BLE_GQ_DEF(m_ble_gatt_queue,                                        /**< BLE GATT Queue instance. */
               NRF_SDH_BLE_CENTRAL_LINK_COUNT,
               NRF_BLE_GQ_QUEUE_SIZE);

static uint16_t m_ble_nus_max_data_len = BLE_GATT_ATT_MTU_DEFAULT - OPCODE_LENGTH - HANDLE_LENGTH; /**< Maximum length of data (in bytes) that can be transmitted to the peer by the Nordic UART service module. */

/**@brief NUS UUID. */
static ble_uuid_t const m_nus_uuid =
{
    .uuid = BLE_UUID_NUS_SERVICE,
    .type = NUS_SERVICE_UUID_TYPE
};


/**@brief Function for handling asserts in the SoftDevice.
 *
 * @details This function is called in case of an assert in the SoftDevice.
 *
 * @warning This handler is only an example and is not meant for the final product. You need to analyze
 *          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(0xDEADBEEF, line_num, p_file_name);
}


/**@brief Function for handling the Nordic UART Service Client errors.
 *
 * @param[in]   nrf_error   Error code containing information about what went wrong.
 */
static void nus_error_handler(uint32_t nrf_error)
{
    APP_ERROR_HANDLER(nrf_error);
}


/**@brief Function to start scanning. */
static void scan_start(void)
{
    ret_code_t ret;

    ret = nrf_ble_scan_start(&m_scan);
    APP_ERROR_CHECK(ret);

    ret = bsp_indication_set(BSP_INDICATE_SCANNING);
    APP_ERROR_CHECK(ret);
}


/**@brief Function for handling Scanning Module events.
 */
static void scan_evt_handler(scan_evt_t const * p_scan_evt)
{
    ret_code_t err_code;

    switch(p_scan_evt->scan_evt_id)
    {
         case NRF_BLE_SCAN_EVT_CONNECTING_ERROR:
         {
              err_code = p_scan_evt->params.connecting_err.err_code;
              APP_ERROR_CHECK(err_code);
         } break;

         case NRF_BLE_SCAN_EVT_CONNECTED:
         {
              ble_gap_evt_connected_t const * p_connected =
                               p_scan_evt->params.connected.p_connected;
             // Scan is automatically stopped by the connection.
             NRF_LOG_INFO("Connecting to target %02x%02x%02x%02x%02x%02x",
                      p_connected->peer_addr.addr[0],
                      p_connected->peer_addr.addr[1],
                      p_connected->peer_addr.addr[2],
                      p_connected->peer_addr.addr[3],
                      p_connected->peer_addr.addr[4],
                      p_connected->peer_addr.addr[5]
                      );
         } break;

         case NRF_BLE_SCAN_EVT_SCAN_TIMEOUT:
         {
             NRF_LOG_INFO("Scan timed out.");
             scan_start();
         } break;

         default:
             break;
    }
}


/**@brief Function for initializing the scanning and setting the filters.
 */
static void scan_init(void)
{
    ble_gap_addr_t m_mac_filter;   
    memset(&m_mac_filter, 0, sizeof(m_mac_filter));

    m_mac_filter.addr[0] = 0x11;
    m_mac_filter.addr[1] = 0x22;
    m_mac_filter.addr[2] = 0x33;
    m_mac_filter.addr[3] = 0x44;
    m_mac_filter.addr[4] = 0x55;
    m_mac_filter.addr[5] = 0x66;
    m_mac_filter.addr_type = BLE_GAP_ADDR_TYPE_PUBLIC;

    ret_code_t          err_code;
    nrf_ble_scan_init_t init_scan;

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

    init_scan.connect_if_match = true;
    init_scan.conn_cfg_tag     = APP_BLE_CONN_CFG_TAG;

    err_code = nrf_ble_scan_init(&m_scan, &init_scan, scan_evt_handler);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_ble_scan_filter_set(&m_scan, SCAN_ADDR_FILTER, &m_mac_filter.addr);

    err_code = nrf_ble_scan_filters_enable(&m_scan, NRF_BLE_SCAN_ADDR_FILTER, false);

    /*NRF_LOG_INFO("Filter address (before activating) %x:%x:%x:%x:%x:%x TYPE %d",
            m_mac_filter.addr[0],
            m_mac_filter.addr[1],
            m_mac_filter.addr[2],
            m_mac_filter.addr[3],
            m_mac_filter.addr[4],
            m_mac_filter.addr[5],
            m_mac_filter.addr_type);*/

    NRF_LOG_INFO("Filter address (before activating) %x:%x:%x:%x:%x:%x",
        m_mac_filter.addr[0],
        m_mac_filter.addr[1],
        m_mac_filter.addr[2],
        m_mac_filter.addr[3],
        m_mac_filter.addr[4],
        m_mac_filter.addr[5]);
    NRF_LOG_INFO("Filter address type (before activating): %d", m_mac_filter.addr_type);


    nrf_ble_scan_filters_t filters;
    memset(&filters, 0, sizeof(nrf_ble_scan_filters_t));
    nrf_ble_scan_filter_get(&m_scan, &filters);
    NRF_LOG_INFO("Filter address (after activating): COUNT=N/A ENABLED=N/A ADDRESS=%x:%x:%x:%x:%x:%x",
          /*filters.addr_filter.addr_cnt,
          filters.addr_filter.addr_filter_enabled,*/
          filters.addr_filter.target_addr[0].addr[0],
          filters.addr_filter.target_addr[0].addr[1],
          filters.addr_filter.target_addr[0].addr[2],
          filters.addr_filter.target_addr[0].addr[3],
          filters.addr_filter.target_addr[0].addr[4],
          filters.addr_filter.target_addr[0].addr[5]);

     NRF_LOG_INFO("Filter address type (after activating): %d", filters.addr_filter.target_addr[0].addr_type);

    /*err_code = nrf_ble_scan_filter_set(&m_scan, SCAN_UUID_FILTER, &m_nus_uuid);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_ble_scan_filters_enable(&m_scan, NRF_BLE_SCAN_UUID_FILTER, false);
    APP_ERROR_CHECK(err_code);*/
}


/**@brief Function for handling database discovery events.
 *
 * @details This function is a callback function to handle events from the database discovery module.
 *          Depending on the UUIDs that are discovered, this function forwards the events
 *          to their respective services.
 *
 * @param[in] p_event  Pointer to the database discovery event.
 */
static void db_disc_handler(ble_db_discovery_evt_t * p_evt)
{
    ble_nus_c_on_db_disc_evt(&m_ble_nus_c, p_evt);
}


/**@brief Function for handling characters received by the Nordic UART Service (NUS).
 *
 * @details This function takes a list of characters of length data_len and prints the characters out on UART.
 *          If @ref ECHOBACK_BLE_UART_DATA is set, the data is sent back to sender.
 */
static void ble_nus_chars_received_uart_print(uint8_t * p_data, uint16_t data_len)
{
    ret_code_t ret_val;

    NRF_LOG_DEBUG("Receiving data.");
    NRF_LOG_HEXDUMP_DEBUG(p_data, data_len);

    for (uint32_t i = 0; i < data_len; i++)
    {
        do
        {
            ret_val = app_uart_put(p_data[i]);
            if ((ret_val != NRF_SUCCESS) && (ret_val != NRF_ERROR_BUSY))
            {
                NRF_LOG_ERROR("app_uart_put failed for index 0x%04x.", i);
                APP_ERROR_CHECK(ret_val);
            }
        } while (ret_val == NRF_ERROR_BUSY);
    }
    if (p_data[data_len-1] == '\r')
    {
        while (app_uart_put('\n') == NRF_ERROR_BUSY);
    }
    if (ECHOBACK_BLE_UART_DATA)
    {
        // Send data back to the peripheral.
        do
        {
            ret_val = ble_nus_c_string_send(&m_ble_nus_c, p_data, data_len);
            if ((ret_val != NRF_SUCCESS) && (ret_val != NRF_ERROR_BUSY))
            {
                NRF_LOG_ERROR("Failed sending NUS message. Error 0x%x. ", ret_val);
                APP_ERROR_CHECK(ret_val);
            }
        } while (ret_val == NRF_ERROR_BUSY);
    }
}


/**@brief   Function for handling app_uart events.
 *
 * @details This function receives a single character from the app_uart module and appends it to
 *          a string. The string is sent over BLE when the last character received is a
 *          'new line' '\n' (hex 0x0A) or if the string reaches the maximum data length.
 */
void uart_event_handle(app_uart_evt_t * p_event)
{
    static uint8_t data_array[BLE_NUS_MAX_DATA_LEN];
    static uint16_t index = 0;
    uint32_t ret_val;

    switch (p_event->evt_type)
    {
        /**@snippet [Handling data from UART] */
        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)))
            {
                NRF_LOG_DEBUG("Ready to send data over BLE NUS");
                NRF_LOG_HEXDUMP_DEBUG(data_array, index);

                do
                {
                    ret_val = ble_nus_c_string_send(&m_ble_nus_c, data_array, index);
                    if ( (ret_val != NRF_ERROR_INVALID_STATE) && (ret_val != NRF_ERROR_RESOURCES) )
                    {
                        APP_ERROR_CHECK(ret_val);
                    }
                } while (ret_val == NRF_ERROR_RESOURCES);

                index = 0;
            }
            break;

        /**@snippet [Handling data from UART] */
        case APP_UART_COMMUNICATION_ERROR:
            NRF_LOG_ERROR("Communication error occurred while handling UART.");
            APP_ERROR_HANDLER(p_event->data.error_communication);
            break;

        case APP_UART_FIFO_ERROR:
            NRF_LOG_ERROR("Error occurred in FIFO module used by UART.");
            APP_ERROR_HANDLER(p_event->data.error_code);
            break;

        default:
            break;
    }
}


/**@brief Callback handling Nordic UART Service (NUS) client events.
 *
 * @details This function is called to notify the application of NUS client events.
 *
 * @param[in]   p_ble_nus_c   NUS client handle. This identifies the NUS client.
 * @param[in]   p_ble_nus_evt Pointer to the NUS client event.
 */

/**@snippet [Handling events from the ble_nus_c module] */
static void ble_nus_c_evt_handler(ble_nus_c_t * p_ble_nus_c, ble_nus_c_evt_t const * p_ble_nus_evt)
{
    ret_code_t err_code;

    switch (p_ble_nus_evt->evt_type)
    {
        case BLE_NUS_C_EVT_DISCOVERY_COMPLETE:
            NRF_LOG_INFO("Discovery complete.");
            err_code = ble_nus_c_handles_assign(p_ble_nus_c, p_ble_nus_evt->conn_handle, &p_ble_nus_evt->handles);
            APP_ERROR_CHECK(err_code);

            err_code = ble_nus_c_tx_notif_enable(p_ble_nus_c);
            APP_ERROR_CHECK(err_code);
            NRF_LOG_INFO("Connected to device with Nordic UART Service.");
            break;

        case BLE_NUS_C_EVT_NUS_TX_EVT:
            ble_nus_chars_received_uart_print(p_ble_nus_evt->p_data, p_ble_nus_evt->data_len);
            break;

        case BLE_NUS_C_EVT_DISCONNECTED:
            NRF_LOG_INFO("Disconnected.");
            scan_start();
            break;
    }
}
/**@snippet [Handling events from the ble_nus_c module] */


/**
 * @brief Function for handling shutdown events.
 *
 * @param[in]   event       Shutdown type.
 */
static bool shutdown_handler(nrf_pwr_mgmt_evt_t event)
{
    ret_code_t err_code;

    err_code = bsp_indication_set(BSP_INDICATE_IDLE);
    APP_ERROR_CHECK(err_code);

    switch (event)
    {
        case NRF_PWR_MGMT_EVT_PREPARE_WAKEUP:
            // Prepare wakeup buttons.
            err_code = bsp_btn_ble_sleep_mode_prepare();
            APP_ERROR_CHECK(err_code);
            break;

        default:
            break;
    }

    return true;
}

NRF_PWR_MGMT_HANDLER_REGISTER(shutdown_handler, APP_SHUTDOWN_HANDLER_PRIORITY);


/**@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)
{
    ret_code_t            err_code;
    ble_gap_evt_t const * p_gap_evt = &p_ble_evt->evt.gap_evt;

    switch (p_ble_evt->header.evt_id)
    {
        case BLE_GAP_EVT_CONNECTED:
            err_code = ble_nus_c_handles_assign(&m_ble_nus_c, p_ble_evt->evt.gap_evt.conn_handle, NULL);
            APP_ERROR_CHECK(err_code);

            err_code = bsp_indication_set(BSP_INDICATE_CONNECTED);
            APP_ERROR_CHECK(err_code);

            // start discovery of services. The NUS Client waits for a discovery result
            err_code = ble_db_discovery_start(&m_db_disc, p_ble_evt->evt.gap_evt.conn_handle);
            APP_ERROR_CHECK(err_code);
            break;

        case BLE_GAP_EVT_DISCONNECTED:

            NRF_LOG_INFO("Disconnected. conn_handle: 0x%x, reason: 0x%x",
                         p_gap_evt->conn_handle,
                         p_gap_evt->params.disconnected.reason);
            break;

        case BLE_GAP_EVT_TIMEOUT:
            if (p_gap_evt->params.timeout.src == BLE_GAP_TIMEOUT_SRC_CONN)
            {
                NRF_LOG_INFO("Connection Request timed out.");
            }
            break;

        case BLE_GAP_EVT_SEC_PARAMS_REQUEST:
            // Pairing not supported.
            err_code = sd_ble_gap_sec_params_reply(p_ble_evt->evt.gap_evt.conn_handle, BLE_GAP_SEC_STATUS_PAIRING_NOT_SUPP, NULL, NULL);
            APP_ERROR_CHECK(err_code);
            break;

        case BLE_GAP_EVT_CONN_PARAM_UPDATE_REQUEST:
            // Accepting parameters requested by peer.
            err_code = sd_ble_gap_conn_param_update(p_gap_evt->conn_handle,
                                                    &p_gap_evt->params.conn_param_update_request.conn_params);
            APP_ERROR_CHECK(err_code);
            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_GATTC_EVT_TIMEOUT:
            // Disconnect on GATT Client timeout event.
            NRF_LOG_DEBUG("GATT Client Timeout.");
            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.
            NRF_LOG_DEBUG("GATT Server Timeout.");
            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:
            break;
    }
}


/**@brief Function for initializing the BLE stack.
 *
 * @details 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 GATT library. */
void gatt_evt_handler(nrf_ble_gatt_t * p_gatt, nrf_ble_gatt_evt_t const * p_evt)
{
    if (p_evt->evt_id == NRF_BLE_GATT_EVT_ATT_MTU_UPDATED)
    {
        NRF_LOG_INFO("ATT MTU exchange completed.");

        m_ble_nus_max_data_len = p_evt->params.att_mtu_effective - OPCODE_LENGTH - HANDLE_LENGTH;
        NRF_LOG_INFO("Ble NUS max data length set to 0x%X(%d)", m_ble_nus_max_data_len, m_ble_nus_max_data_len);
    }
}


/**@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_central_set(&m_gatt, NRF_SDH_BLE_GATT_MAX_MTU_SIZE);
    APP_ERROR_CHECK(err_code);
}


/**@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)
{
    ret_code_t err_code;

    switch (event)
    {
        case BSP_EVENT_SLEEP:
            nrf_pwr_mgmt_shutdown(NRF_PWR_MGMT_SHUTDOWN_GOTO_SYSOFF);
            break;

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

        default:
            break;
    }
}

/**@brief Function for initializing the UART. */
static void uart_init(void)
{
    ret_code_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,
        .baud_rate    = UART_BAUDRATE_BAUDRATE_Baud115200
    };

    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);
}

/**@brief Function for initializing the Nordic UART Service (NUS) client. */
static void nus_c_init(void)
{
    ret_code_t       err_code;
    ble_nus_c_init_t init;

    init.evt_handler   = ble_nus_c_evt_handler;
    init.error_handler = nus_error_handler;
    init.p_gatt_queue  = &m_ble_gatt_queue;

    err_code = ble_nus_c_init(&m_ble_nus_c, &init);
    APP_ERROR_CHECK(err_code);
}


/**@brief Function for initializing buttons and leds. */
static void buttons_leds_init(void)
{
    ret_code_t err_code;
    bsp_event_t startup_event;

    err_code = bsp_init(BSP_INIT_LEDS, bsp_event_handler);
    APP_ERROR_CHECK(err_code);

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


/**@brief Function for initializing the timer. */
static void timer_init(void)
{
    ret_code_t err_code = app_timer_init();
    APP_ERROR_CHECK(err_code);
}


/**@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 initializing the database discovery module. */
static void db_discovery_init(void)
{
    ble_db_discovery_init_t db_init;

    memset(&db_init, 0, sizeof(ble_db_discovery_init_t));

    db_init.evt_handler  = db_disc_handler;
    db_init.p_gatt_queue = &m_ble_gatt_queue;

    ret_code_t err_code = ble_db_discovery_init(&db_init);
    APP_ERROR_CHECK(err_code);
}


/**@brief Function for handling the idle state (main loop).
 *
 * @details Handles any pending log operations, then sleeps until the next event occurs.
 */
static void idle_state_handle(void)
{
    if (NRF_LOG_PROCESS() == false)
    {
        nrf_pwr_mgmt_run();
    }
}


int main(void)
{
    // Initialize.
    log_init();
    timer_init();
    uart_init();
    buttons_leds_init();
    db_discovery_init();
    power_management_init();
    ble_stack_init();
    gatt_init();
    nus_c_init();
    scan_init();

    // Start execution.
    printf("BLE UART central example started.\r\n");
    NRF_LOG_INFO("BLE UART central example started.");
    scan_start();

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

I got the following output:

<info> app_timer: RTC: initialized.
<info> app: Filter address (before activating) 11:22:33:44:55:66
<info> app: Filter address type (before activating): 0
<info> app: Filter address (after activating): COUNT=N/A ENABLED=N/A ADDRESS=11:22:33:44:55:66
<info> app: Filter address type (after activating): 0
<info> app: BLE UART central example started.

Could you check if you are getting the same output?

Best regards,

Simon