custom service discovery in BLE_Central

[Prajakta]

Hi,

I want to develop central code to discover services of 3rd party device and to discover their services and read/write characteristics.

As seen many examples from SDK below is my understanding:

1. Include db_discovery_init() 

2. call ble_db_discovery_start() on BLE_GAP_EVT_CONNECTED event in ble_evt_handler().

3. While initlaizing need to init service which is going to discover as below:

like in BLE_blinky example,includes ble_lbs service as below :

static void db_disc_handler(ble_db_discovery_evt_t * p_evt)
{
    ble_lbs_on_db_disc_evt(&m_ble_lbs_c, p_evt);
}

So my question is:

While db_discovery_init() which service should initialize in db_disc_handler() for custom service discovery? when we don't know which service is advertising by other device.

And

How to discover the services and print this and its characteristics on console. Same as we can see in nrf Connect app. Please suggest or share suitable code except BLE_UART example code.

Please help me on this asap.

Regards,

Prajakta

[Hung Bui]

Hi Prajakta, 

The db_disc_handler() is where you handle the events from the db discovery library, for example when the discovery is complete, or when the service is not found. 

However, the db discovery module was not really made for generic service discovery. This means usually you need to provide the service UUID(s) you want to discover to the module before it started. 

To be able to do generic discovery (where you discovery all UUIDs) you would need to modify it a little bit. There is some discussion here. Please have a look and let me know if you have any question. 

[Prajakta]

I am using BLE_Blinky application, in that after connection done, in ble_evt_handler (),handle_assign function is there, then they called ble_db_discovery_start.

As per this discussion, need to call sd_ble_gattc_primary_services_discover.
1.So where I can call this function with parameters?

And

2. Can you help me for flow for service discovery from start(init) to end in example code.I am able to do it for ble_lbs_c service(blinky application). I am not getting how to replicate it for primary service discovery.

[Prajakta]

Thank you so much Hung Bui....

It also works for me.
but now the issue is in on_primary_srv_discovery_rsp.

if (p_ble_gattc_evt->conn_handle != p_db_discovery->conn_handle)
{
NRF_LOG_INFO("Return from on_primary_srv_discovery_rsp");
return;
}

is something i am doing wrong?

[Prajakta]

i am able to discover service. but at time only 1 service is discovered.

I think this is because as you said in previous conversation.
Then you can continue to call sd_ble_gattc_primary_services_discover() with the last handle until you receive ATTRIBUTE_NOT_FOUND in the next correspondent event .

But how to do it. Can you help me to add this in code. Please

[Hung Bui]

Good to see you get some progress. 

Please make sure you check the .count in the return argument , there can be more than one service discovered. 

Then you should check the last service discovered and find the handle_range, find the end_handle of that range. From that you can discovery the next service by calling sd_ble_gattc_primary_services_discover with the start_handle equal end_handle + 1. 

And continue doing so until you receive ATTRIBUTE_NOT_FOUND

[Prajakta]

<Please make sure you check the .count in the return argument , there can be more than one service discovered. >

where to check in code?

I have checked it here p_db_discovery->srv_count; it gives count = 0.

[Prajakta]

I have one another issue.
1.I am trying to replicate nrf Connect screenshot in receiver code.Attached.

/resized-image/__size/320x240/__key/communityserver-discussions-components-files/4/Screenshot_5F00_20181116_2D00_205137.png

/resized-image/__size/320x240/__key/communityserver-discussions-components-files/4/Screenshot_5F00_20181116_2D00_205137.png

/resized-image/__size/320x240/__key/communityserver-discussions-components-files/4/Screenshot_5F00_20181116_2D00_205131.png

2. While first 3 services and its characteristics get correctly, below is output for one service(because i am able to discover one service at a time):

nfo> app: Discovery done successfully..
<info> ble_db_disc: Found services in.............
<info> ble_db_disc: current discovery count:0
<info> ble_db_disc: current service index: 0
<info> ble_db_disc: Found service UUID 1800 and its start handle:1 , End handle: 7
<info> ble_db_disc: Number of characteristics: 3
<info> ble_db_disc: discovered Characteristics = 2A00 & its Properties:
 Read = 1
, Write = 1
, WriteWoResp = 0
,notify = 0
, Indicate = 0
<info> ble_db_disc: discovered Characteristics = 2A01 & its Properties:
 Read = 1
, Write = 0
, WriteWoResp = 0
,notify = 0
, Indicate = 0
<info> ble_db_disc: discovered Characteristics = 2A04 & its Properties:
 Read = 1
, Write = 0
, WriteWoResp = 0
,notify = 0,Indicate = 0

3.Last one of unknown UUID, Start_handle and end_handle is zero. i am getting below output:

<info> app: Discovery done successfully..
<info> ble_db_disc: Found services in.............
<info> ble_db_disc: current discovery count:5
<info> ble_db_disc: current service index: 0
<info> ble_db_disc: Found service UUID 5D4 and its start handle:0 , End handle: 0

4. Attaching ble_db_dicsovery file where this all changes are made.

 

Fullscreen 4760.ble_db_discovery.c Download

/**
 * Copyright (c) 2013 - 2018, Nordic Semiconductor ASA
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form, except as embedded into a Nordic
 *    Semiconductor ASA integrated circuit in a product or a software update for
 *    such product, must reproduce the above copyright notice, this list of
 *    conditions and the following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 *
 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
 *
 * 5. Any software provided in binary form under this license must not be reverse
 *    engineered, decompiled, modified and/or disassembled.
 *
 * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY, NONINFRINGEMENT, AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL NORDIC SEMICONDUCTOR ASA OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

#include "sdk_common.h"

#if NRF_MODULE_ENABLED(BLE_DB_DISCOVERY)
#include "ble_db_discovery.h"
#include <stdlib.h>
#include "ble_srv_common.h"
#define NRF_LOG_MODULE_NAME ble_db_disc
#include "nrf_log.h"
NRF_LOG_MODULE_REGISTER();

#define SRV_DISC_START_HANDLE  0x0001                    /**< The start handle value used during service discovery. */
#define DB_DISCOVERY_MAX_USERS BLE_DB_DISCOVERY_MAX_SRV  /**< The maximum number of users/registrations allowed by this module. */
#define MODULE_INITIALIZED (m_initialized == true)       /**< Macro designating whether the module has been initialized properly. */


/**@brief Array of structures containing information about the registered application modules. */
static ble_uuid_t m_registered_handlers[DB_DISCOVERY_MAX_USERS];


/**@brief   Array of structures containing pending events to be sent to the application modules.
 *
 * @details Whenever a discovery related event is to be raised to a user module, it will be stored
 *          in this array first. When all services needed to be discovered have been
 *          discovered, all pending events will be sent to the corresponding user modules.
 **/
static struct
{
    ble_db_discovery_evt_t         evt;          /**< The pending event. */
    ble_db_discovery_evt_handler_t evt_handler;  /**< The event handler which should be called to raise this event. */
} m_pending_user_evts[DB_DISCOVERY_MAX_USERS];

static ble_db_discovery_evt_handler_t m_evt_handler;
static uint32_t m_pending_usr_evt_index;    /**< The index to the pending user event array, pointing to the last added pending user event. */
static uint32_t m_num_of_handlers_reg;      /**< The number of handlers registered with the DB Discovery module. */
static bool     m_initialized = false;      /**< This variable Indicates if the module is initialized or not. */

/**@brief     Function for fetching the event handler provided by a registered application module.
 *
 * @param[in] srv_uuid UUID of the service.
 *
 * @retval    evt_handler Event handler of the module, registered for the given service UUID.
 * @retval    NULL If no event handler is found.
 */
static ble_db_discovery_evt_handler_t registered_handler_get(ble_uuid_t const * p_srv_uuid)
{
    for (uint32_t i = 0; i < m_num_of_handlers_reg; i++)
    {
        if (BLE_UUID_EQ(&(m_registered_handlers[i]), p_srv_uuid))
        {
            return (m_evt_handler);
        }
    }

    return NULL;
}


/**@brief     Function for storing the event handler provided by a registered application module.
 *
 * @param[in] p_srv_uuid    The UUID of the service.
 * @param[in] p_evt_handler The event handler provided by the application.
 *
 * @retval    NRF_SUCCESS If the handler was stored or already present in the list.
 * @retval    NRF_ERROR_NO_MEM If there is no space left to store the handler.
 */
static uint32_t registered_handler_set(ble_uuid_t                     const * p_srv_uuid,
                                       ble_db_discovery_evt_handler_t         p_evt_handler)
{
    if (registered_handler_get(p_srv_uuid) != NULL)
    {
        return NRF_SUCCESS;
    }

    if (m_num_of_handlers_reg < DB_DISCOVERY_MAX_USERS)
    {
        m_registered_handlers[m_num_of_handlers_reg] = *p_srv_uuid;
        m_num_of_handlers_reg++;

        return NRF_SUCCESS;
    }
    else
    {
        return NRF_ERROR_NO_MEM;
    }
}


/**@brief Function for sending all pending discovery events to the corresponding user modules.
 */
static void pending_user_evts_send(void)
{
    for (uint32_t i = 0; i < m_num_of_handlers_reg; i++)
    {
        // Pass the event to the corresponding event handler.
        m_pending_user_evts[i].evt_handler(&(m_pending_user_evts[i].evt));
    }

    m_pending_usr_evt_index = 0;
}


/**@brief     Function for indicating error to the application.
 *
 * @details   This function will fetch the event handler based on the UUID of the service being
 *            discovered. (The event handler is registered by the application beforehand).
 *            The error code is added to the pending events together with the event handler.
 *            If no event handler was found, then this function will do nothing.
 *
 * @param[in] p_db_discovery Pointer to the DB discovery structure.
 * @param[in] err_code       Error code that should be provided to the application.
 * @param[in] conn_handle    Connection Handle.
 *
 */
static void discovery_error_evt_trigger(ble_db_discovery_t * p_db_discovery,
                                        uint32_t             err_code,
                                        uint16_t             conn_handle)
{
    ble_db_discovery_evt_handler_t   p_evt_handler;
    ble_gatt_db_srv_t              * p_srv_being_discovered;

    p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]);

    p_evt_handler = registered_handler_get(&(p_srv_being_discovered->srv_uuid));

    if (p_evt_handler != NULL)
    {
        ble_db_discovery_evt_t evt =
        {
            .conn_handle     = conn_handle,
            .evt_type        = BLE_DB_DISCOVERY_ERROR,
            .params.err_code = err_code,
        };

        p_evt_handler(&evt);
    }
}


/**@brief     Function for triggering a Discovery Complete or Service Not Found event to the
 *            application.
 *
 * @details   This function will fetch the event handler based on the UUID of the service being
 *            discovered. (The event handler is registered by the application beforehand).
 *            It then triggers an event indicating the completion of the service discovery.
 *            If no event handler was found, then this function will do nothing.
 *
 * @param[in] p_db_discovery Pointer to the DB discovery structure.
 * @param[in] is_srv_found   Variable to indicate if the service was found at the peer.
 * @param[in] conn_handle    Connection Handle.
 */
static void discovery_complete_evt_trigger(ble_db_discovery_t * p_db_discovery,
                                           bool                 is_srv_found,
                                           uint16_t             conn_handle)
{
    ble_db_discovery_evt_handler_t   p_evt_handler;
    ble_gatt_db_srv_t              * p_srv_being_discovered;

    p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]);

    p_evt_handler = registered_handler_get(&(p_srv_being_discovered->srv_uuid));

    if (p_evt_handler != NULL)
    {
        if (m_pending_usr_evt_index < DB_DISCOVERY_MAX_USERS)
        {
            // Insert an event into the pending event list.
            m_pending_user_evts[m_pending_usr_evt_index].evt.conn_handle = conn_handle;
            m_pending_user_evts[m_pending_usr_evt_index].evt.params.discovered_db =
                *p_srv_being_discovered;

            if (is_srv_found)
            {
                m_pending_user_evts[m_pending_usr_evt_index].evt.evt_type =
                    BLE_DB_DISCOVERY_COMPLETE;
            }
            else
            {
                m_pending_user_evts[m_pending_usr_evt_index].evt.evt_type =
                    BLE_DB_DISCOVERY_SRV_NOT_FOUND;
            }

            m_pending_user_evts[m_pending_usr_evt_index].evt_handler = p_evt_handler;
            m_pending_usr_evt_index++;

            if (m_pending_usr_evt_index == m_num_of_handlers_reg)
            {
                // All registered modules have pending events. Send all pending events to the user
                // modules.
                pending_user_evts_send();
            }
            else
            {
                // Too many events pending. Do nothing. (Ideally this should not happen.)
            }
        }
    }
}


/**@brief     Function for handling service discovery completion.
 *
 * @details   This function will be used to determine if there are more services to be discovered,
 *            and if so, initiate the discovery of the next service.
 *
 * @param[in] p_db_discovery Pointer to the DB Discovery Structure.
 * @param[in] conn_handle    Connection Handle.
 */
static void on_srv_disc_completion(ble_db_discovery_t * p_db_discovery,
                                   uint16_t             conn_handle)
{
    p_db_discovery->discoveries_count++;
   // NRF_LOG_INFO("incremented discovery count:%d",p_db_discovery->discoveries_count);

    // Check if more services need to be discovered.
    if (p_db_discovery->discoveries_count < m_num_of_handlers_reg)
    {
        // Reset the current characteristic index since a new service discovery is about to start.
        p_db_discovery->curr_char_ind = 0;

        // Initiate discovery of the next service.

        p_db_discovery->curr_srv_ind++;
       // NRF_LOG_INFO("incremented service index: %d",p_db_discovery->curr_srv_ind);

        ble_gatt_db_srv_t * p_srv_being_discovered;

        p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]);

        p_srv_being_discovered->srv_uuid = m_registered_handlers[p_db_discovery->curr_srv_ind];

        // Reset the characteristic count in the current service to zero since a new service
        // discovery is about to start.
        p_srv_being_discovered->char_count = 0;

        NRF_LOG_INFO("Starting discovery of servicce with UUID 0x%x on connection handle 0x%x.",
                      p_srv_being_discovered->srv_uuid.uuid, conn_handle);

        uint32_t err_code;

        err_code = sd_ble_gattc_primary_services_discover(conn_handle,
                                                          SRV_DISC_START_HANDLE,
                                                          &(p_srv_being_discovered->srv_uuid));

        if (err_code != NRF_SUCCESS)
        {
            p_db_discovery->discovery_in_progress = false;

            // Error with discovering the service.
            // Indicate the error to the registered user application.
            discovery_error_evt_trigger(p_db_discovery, err_code, conn_handle);

            m_pending_user_evts[0].evt.evt_type    = BLE_DB_DISCOVERY_AVAILABLE;
            m_pending_user_evts[0].evt.conn_handle = conn_handle;

            return;
        }
    }
    else
    {
        // No more service discovery is needed.
        p_db_discovery->discovery_in_progress  = false;
        m_pending_user_evts[0].evt.evt_type    = BLE_DB_DISCOVERY_AVAILABLE;
        m_pending_user_evts[0].evt.conn_handle = conn_handle;
    }
}


/**@brief     Function for finding out if a characteristic discovery should be performed after the
 *            last discovered characteristic.
 *
 * @details   This function is used during the time of database discovery to find out if there is
 *            a need to do more characteristic discoveries. The value handles of the
 *            last discovered characteristic is compared with the end handle of the service.
 *            If the service handle is greater than one of the former characteristic handles,
 *            it means that a characteristic discovery is required.
 *
 * @param[in] p_db_discovery The pointer to the DB Discovery structure.
 * @param[in] p_after_char   The pointer to the last discovered characteristic.
 *
 * @retval    True if a characteristic discovery is required.
 * @retval    False if a characteristic discovery is NOT required.
 */
static bool is_char_discovery_reqd(ble_db_discovery_t * p_db_discovery,
                                   ble_gattc_char_t   * p_after_char)
{
    if (p_after_char->handle_value <
        p_db_discovery->services[p_db_discovery->curr_srv_ind].handle_range.end_handle)
    {
        // Handle value of the characteristic being discovered is less than the end handle of
        // the service being discovered. There is a possibility of more characteristics being
        // present. Hence a characteristic discovery is required.
        return true;
    }

    return false;
}


/**@brief      Function to find out if a descriptor discovery is required.
 *
 * @details    This function finds out if there is a possibility of existence of descriptors between
 *             current characteristic and the next characteristic. If so, this function will compute
 *             the handle range on which the descriptors may be present and will return it.
 *             If the current characteristic is the last known characteristic, then this function
 *             will use the service end handle to find out if the current characteristic can have
 *             descriptors.
 *
 * @param[in]  p_db_discovery Pointer to the DB Discovery structure.
 * @param[in]  p_curr_char    Pointer to the current characteristic.
 * @param[in]  p_next_char    Pointer to the next characteristic. This should be NULL if the
 *                            caller knows that there is no characteristic after the current
 *                            characteristic at the peer.
 * @param[out] p_handle_range Pointer to the handle range in which descriptors may exist at the
 *                            the peer.
 *
 * @retval     True If a descriptor discovery is required.
 * @retval     False If a descriptor discovery is NOT required.
 */
static bool is_desc_discovery_reqd(ble_db_discovery_t       * p_db_discovery,
                                   ble_gatt_db_char_t       * p_curr_char,
                                   ble_gatt_db_char_t       * p_next_char,
                                   ble_gattc_handle_range_t * p_handle_range)
{
    if (p_next_char == NULL)
    {
        // Current characteristic is the last characteristic in the service. Check if the value
        // handle of the current characteristic is equal to the service end handle.
        if (
            p_curr_char->characteristic.handle_value ==
            p_db_discovery->services[p_db_discovery->curr_srv_ind].handle_range.end_handle
           )
        {
            // No descriptors can be present for the current characteristic. p_curr_char is the last
            // characteristic with no descriptors.
            return false;
        }

        p_handle_range->start_handle = p_curr_char->characteristic.handle_value + 1;

        // Since the current characteristic is the last characteristic in the service, the end
        // handle should be the end handle of the service.
        p_handle_range->end_handle =
            p_db_discovery->services[p_db_discovery->curr_srv_ind].handle_range.end_handle;

        return true;
    }

    // p_next_char != NULL. Check for existence of descriptors between the current and the next
    // characteristic.
    if ((p_curr_char->characteristic.handle_value + 1) == p_next_char->characteristic.handle_decl)
    {
        // No descriptors can exist between the two characteristic.
        return false;
    }

    p_handle_range->start_handle = p_curr_char->characteristic.handle_value + 1;
    p_handle_range->end_handle   = p_next_char->characteristic.handle_decl - 1;

    return true;
}


/**@brief     Function for performing characteristic discovery.
 *
 * @param[in] p_db_discovery Pointer to the DB Discovery structure.
 * @param[in] conn_handle    Connection Handle.
 *
 * @return    NRF_SUCCESS if the SoftDevice was successfully requested to perform the characteristic
 *            discovery. Otherwise an error code. This function returns the error code returned
 *            by the SoftDevice API @ref sd_ble_gattc_characteristics_discover.
 */
static uint32_t characteristics_discover(ble_db_discovery_t * p_db_discovery,
                                         uint16_t             conn_handle)
{
    ble_gatt_db_srv_t      * p_srv_being_discovered;
    ble_gattc_handle_range_t handle_range;

    p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]);

    if (p_db_discovery->curr_char_ind != 0)
    {
        // This is not the first characteristic being discovered. Hence the 'start handle' to be
        // used must be computed using the handle_value of the previous characteristic.
        ble_gattc_char_t * p_prev_char;
        uint8_t            prev_char_ind = p_db_discovery->curr_char_ind - 1;

        p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]);

        p_prev_char = &(p_srv_being_discovered->charateristics[prev_char_ind].characteristic);
      //  NRF_LOG_INFO("Characteristics: %x",p_prev_char);
        handle_range.start_handle = p_prev_char->handle_value + 1;
    }
    else
    {
        // This is the first characteristic of this service being discovered.
        handle_range.start_handle = p_srv_being_discovered->handle_range.start_handle;
    }

    handle_range.end_handle = p_srv_being_discovered->handle_range.end_handle;

    return sd_ble_gattc_characteristics_discover(conn_handle, &handle_range);
}


/**@brief      Function for performing descriptor discovery, if required.
 *
 * @details    This function will check if descriptor discovery is required and then perform it if
 *             needed. If no more descriptor discovery is required for the service, then the output
 *             parameter p_raise_discov_complete is set to true, indicating to the caller that a
 *             discovery complete event can be triggered to the application.
 *
 * @param[in]  p_db_discovery           Pointer to the DB Discovery structure.
 * @param[out] p_raise_discov_complete  The value pointed to by this pointer will be set to true if
 *                                      the Discovery Complete event can be triggered to the
 *                                      application.
 * @param[in] conn_handle               Connection Handle.
 *
 * @return     NRF_SUCCESS if the SoftDevice was successfully requested to perform the descriptor
 *             discovery, or if no more descriptor discovery is required. Otherwise an error code.
 *             This function returns the error code returned by the SoftDevice API @ref
 *             sd_ble_gattc_descriptors_discover.
 */
static uint32_t descriptors_discover(ble_db_discovery_t * p_db_discovery,
                                     bool               * p_raise_discov_complete,
                                     uint16_t             conn_handle)
{
    ble_gattc_handle_range_t   handle_range;
    ble_gatt_db_char_t       * p_curr_char_being_discovered;
    ble_gatt_db_srv_t        * p_srv_being_discovered;
    bool                       is_discovery_reqd = false;

    p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]);

    p_curr_char_being_discovered =
        &(p_srv_being_discovered->charateristics[p_db_discovery->curr_char_ind]);

    if ((p_db_discovery->curr_char_ind + 1) == p_srv_being_discovered->char_count)
    {
        // This is the last characteristic of this service.
        is_discovery_reqd = is_desc_discovery_reqd(p_db_discovery,
                                                   p_curr_char_being_discovered,
                                                   NULL,
                                                   &handle_range);
    }
    else
    {
        uint8_t                   i;
        ble_gatt_db_char_t * p_next_char;

        for (i = p_db_discovery->curr_char_ind; i < p_srv_being_discovered->char_count; i++)
        {
            if (i == (p_srv_being_discovered->char_count - 1))
            {
                // The current characteristic is the last characteristic in the service.
                p_next_char = NULL;
            }
            else
            {
                p_next_char = &(p_srv_being_discovered->charateristics[i + 1]);
            }

            // Check if it is possible for the current characteristic to have a descriptor.
            if (is_desc_discovery_reqd(p_db_discovery,
                                       p_curr_char_being_discovered,
                                       p_next_char,
                                       &handle_range))
            {
                is_discovery_reqd = true;
                break;
            }
            else
            {
                // No descriptors can exist.
                p_curr_char_being_discovered = p_next_char;
                p_db_discovery->curr_char_ind++;
            }
        }
    }

    if (!is_discovery_reqd)
    {
        // No more descriptor discovery required. Discovery is complete.
        // This informs the caller that a discovery complete event can be triggered.
        *p_raise_discov_complete = true;

        return NRF_SUCCESS;
    }

    *p_raise_discov_complete = false;

    return sd_ble_gattc_descriptors_discover(conn_handle, &handle_range);
}


/**@brief     Function for handling primary service discovery response.
 *
 * @details   This function will handle the primary service discovery response and start the
 *            discovery of characteristics within that service.
 *
 * @param[in] p_db_discovery    Pointer to the DB Discovery structure.
 * @param[in] p_ble_gattc_evt   Pointer to the GATT Client event.
 */
void on_primary_srv_discovery_rsp(ble_db_discovery_t       * p_db_discovery,
                                         ble_gattc_evt_t    const * p_ble_gattc_evt)
{
    ble_gatt_db_srv_t * p_srv_being_discovered;
    int start_handle = 0;
    uint32_t err_code;
    //NRF_LOG_INFO("In on_primary_srv_discovery_rsp");
    p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]);
  //  uint8_t num_srv_disc = p_db_discovery->srv_count;
//int i;

    if (p_ble_gattc_evt->conn_handle != p_db_discovery->conn_handle)
    {
    	// NRF_LOG_INFO("Return from on_primary_srv_discovery_rsp");
   // 	return;
    }
    //NRF_LOG_INFO("Number of services discovered: %d ",num_srv_disc);
    if (p_ble_gattc_evt->gatt_status == BLE_GATT_STATUS_SUCCESS)
    {

        ble_gattc_evt_prim_srvc_disc_rsp_t const * p_prim_srvc_disc_rsp_evt;
        uint32_t err_code;
        p_prim_srvc_disc_rsp_evt = &(p_ble_gattc_evt->params.prim_srvc_disc_rsp);
	//for(i=0; i < 4; i++)
	//{
		p_srv_being_discovered->srv_uuid     = p_prim_srvc_disc_rsp_evt->services[3].uuid;
        p_srv_being_discovered->handle_range = p_prim_srvc_disc_rsp_evt->services[3].handle_range;

        NRF_LOG_INFO("Found service UUID %x and its start handle:%d , End handle: %d", p_srv_being_discovered->srv_uuid.uuid,
        		p_srv_being_discovered->handle_range.start_handle, p_srv_being_discovered->handle_range.end_handle);
	//}
        start_handle = (p_srv_being_discovered->handle_range.end_handle) + 1;
        err_code = characteristics_discover(p_db_discovery, p_ble_gattc_evt->conn_handle);

        if (err_code != NRF_SUCCESS)
        {
            p_db_discovery->discovery_in_progress = false;

           // NRF_LOG_INFO("Error with discovering the characteristics");
            // Indicate the error to the registered user application.
            discovery_error_evt_trigger(p_db_discovery, err_code, p_ble_gattc_evt->conn_handle);

            m_pending_user_evts[0].evt.evt_type    = BLE_DB_DISCOVERY_AVAILABLE;
            m_pending_user_evts[0].evt.conn_handle = p_ble_gattc_evt->conn_handle;
        }
    }
    else
    {
        NRF_LOG_INFO("Service UUID 0x%x not found.", p_srv_being_discovered->srv_uuid.uuid);
        // Trigger Service Not Found event to the application.
        discovery_complete_evt_trigger(p_db_discovery, false, p_ble_gattc_evt->conn_handle);
        on_srv_disc_completion(p_db_discovery, p_ble_gattc_evt->conn_handle);
    }
    if(p_ble_gattc_evt->gatt_status != BLE_GATT_STATUS_ATTERR_ATTRIBUTE_NOT_FOUND)
    {

        err_code = sd_ble_gattc_primary_services_discover( p_db_discovery->conn_handle,
        													start_handle,NULL);

        	if(err_code == NRF_SUCCESS)
           {
        		NRF_LOG_INFO("Discovery done successfully..");
           }
        	else
        	{
        		NRF_LOG_INFO("Discovery Fail..");

        	}
    }


    //on_srv_disc_completion(p_db_discovery, p_ble_gattc_evt->conn_handle);
}


/**@brief     Function for handling characteristic discovery response.
 *
 * @param[in] p_db_discovery    Pointer to the DB Discovery structure.
 * @param[in] p_ble_gattc_evt   Pointer to the GATT Client event.
 */
static void on_characteristic_discovery_rsp(ble_db_discovery_t       * p_db_discovery,
                                            ble_gattc_evt_t    const * p_ble_gattc_evt)
{
    uint32_t            err_code;
    ble_gatt_db_srv_t * p_srv_being_discovered;
    bool                perform_desc_discov = false;

    if (p_ble_gattc_evt->conn_handle != p_db_discovery->conn_handle)
    {
        //return;
    }

    p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]);

    if (p_ble_gattc_evt->gatt_status == BLE_GATT_STATUS_SUCCESS)
    {
        ble_gattc_evt_char_disc_rsp_t const * p_char_disc_rsp_evt;

        p_char_disc_rsp_evt = &(p_ble_gattc_evt->params.char_disc_rsp);

        // Find out the number of characteristics that were previously discovered (in earlier
        // characteristic discovery responses, if any).
        uint8_t num_chars_prev_disc = p_srv_being_discovered->char_count;

        // Find out the number of characteristics that are currently discovered (in the
        // characteristic discovery response being handled).
        uint8_t num_chars_curr_disc = p_char_disc_rsp_evt->count;


        // Check if the total number of discovered characteristics are supported by this module.
        if ((num_chars_prev_disc + num_chars_curr_disc) <= BLE_GATT_DB_MAX_CHARS)
        {
            // Update the characteristics count.
            p_srv_being_discovered->char_count += num_chars_curr_disc;
            NRF_LOG_INFO("Number of characteristics: %d",num_chars_curr_disc);
        }
        else
        {
            // The number of characteristics discovered at the peer is more than the supported
            // maximum. This module will store only the characteristics found up to this point.
            p_srv_being_discovered->char_count = BLE_GATT_DB_MAX_CHARS;
            NRF_LOG_INFO("Not enough space for characteristics associated with "
                            "service 0x%04X !", p_srv_being_discovered->srv_uuid.uuid);
            NRF_LOG_WARNING("Increase BLE_GATT_DB_MAX_CHARS to be able to store more "
                            "characteristics for each service!");
        }

        uint32_t i;
        uint32_t j;

        for (i = num_chars_prev_disc, j = 0; i < p_srv_being_discovered->char_count; i++, j++)
        {
            p_srv_being_discovered->charateristics[i].characteristic =
                p_char_disc_rsp_evt->chars[j];
//int num = p_srv_being_discovered->charateristics[i].characteristic.uuid.uuid;
//NRF_LOG_INFO("discovered %d",num);

        	NRF_LOG_INFO("discovered Characteristics = %x & its Properties:\n\rRead = %d\n\rWrite = %d\n\rWriteWoResp = %d\n\r"
        			"""notify = %d\n\rIndicate = %d",
					p_srv_being_discovered->charateristics[i].characteristic.uuid.uuid,
					p_srv_being_discovered->charateristics[i].characteristic.char_props.read,
					p_srv_being_discovered->charateristics[i].characteristic.char_props.write,
					p_srv_being_discovered->charateristics[i].characteristic.char_props.write_wo_resp,
					p_srv_being_discovered->charateristics[i].characteristic.char_props.notify,
					p_srv_being_discovered->charateristics[i].characteristic.char_props.indicate);

            p_srv_being_discovered->charateristics[i].cccd_handle       = BLE_GATT_HANDLE_INVALID;
            p_srv_being_discovered->charateristics[i].ext_prop_handle   = BLE_GATT_HANDLE_INVALID;
            p_srv_being_discovered->charateristics[i].user_desc_handle  = BLE_GATT_HANDLE_INVALID;
            p_srv_being_discovered->charateristics[i].report_ref_handle = BLE_GATT_HANDLE_INVALID;
        }

        ble_gattc_char_t * p_last_known_char;

        p_last_known_char = &(p_srv_being_discovered->charateristics[i - 1].characteristic);

        // If no more characteristic discovery is required, or if the maximum number of supported
        // characteristic per service has been reached, descriptor discovery will be performed.
        if (   !is_char_discovery_reqd(p_db_discovery, p_last_known_char)
            || (p_srv_being_discovered->char_count == BLE_GATT_DB_MAX_CHARS))
        {
            perform_desc_discov = true;
        }
        else
        {
            // Update the current characteristic index.
            p_db_discovery->curr_char_ind = p_srv_being_discovered->char_count;

            // Perform another round of characteristic discovery.
            err_code = characteristics_discover(p_db_discovery, p_ble_gattc_evt->conn_handle);

            if (err_code != NRF_SUCCESS)
            {
                p_db_discovery->discovery_in_progress = false;

                discovery_error_evt_trigger(p_db_discovery, err_code, p_ble_gattc_evt->conn_handle);

                m_pending_user_evts[0].evt.evt_type    = BLE_DB_DISCOVERY_AVAILABLE;
                m_pending_user_evts[0].evt.conn_handle = p_ble_gattc_evt->conn_handle;

                return;
            }
        }
    }
    else
    {
        // The previous characteristic discovery resulted in no characteristics.
        // descriptor discovery should be performed.
        perform_desc_discov = true;
    }

    if (perform_desc_discov)
    {
        bool raise_discov_complete;

        p_db_discovery->curr_char_ind = 0;

        err_code = descriptors_discover(p_db_discovery,
                                        &raise_discov_complete,
                                        p_ble_gattc_evt->conn_handle);

        if (err_code != NRF_SUCCESS)
        {
            p_db_discovery->discovery_in_progress = false;

            discovery_error_evt_trigger(p_db_discovery, err_code, p_ble_gattc_evt->conn_handle);

            m_pending_user_evts[0].evt.evt_type    = BLE_DB_DISCOVERY_AVAILABLE;
            m_pending_user_evts[0].evt.conn_handle = p_ble_gattc_evt->conn_handle;

            return;
        }
        if (raise_discov_complete)
        {
            // No more characteristics and descriptors need to be discovered. Discovery is complete.
            // Send a discovery complete event to the user application.
            NRF_LOG_DEBUG("Discovery of service with UUID 0x%x completed with success"
                          " on connection handle 0x%x.",
                          p_srv_being_discovered->srv_uuid.uuid,
                          p_ble_gattc_evt->conn_handle);

            discovery_complete_evt_trigger(p_db_discovery, true, p_ble_gattc_evt->conn_handle);
            on_srv_disc_completion(p_db_discovery, p_ble_gattc_evt->conn_handle);
        }
    }
}


/**@brief     Function for handling descriptor discovery response.
 *
 * @param[in] p_db_discovery    Pointer to the DB Discovery structure.
 * @param[in] p_ble_gattc_evt   Pointer to the GATT Client event.
 */
static void on_descriptor_discovery_rsp(ble_db_discovery_t * const    p_db_discovery,
                                        const ble_gattc_evt_t * const p_ble_gattc_evt)
{
    const ble_gattc_evt_desc_disc_rsp_t * p_desc_disc_rsp_evt;
    ble_gatt_db_srv_t                   * p_srv_being_discovered;

    if (p_ble_gattc_evt->conn_handle != p_db_discovery->conn_handle)
    {
        return;
    }

    p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]);

    p_desc_disc_rsp_evt = &(p_ble_gattc_evt->params.desc_disc_rsp);

    ble_gatt_db_char_t * p_char_being_discovered =
        &(p_srv_being_discovered->charateristics[p_db_discovery->curr_char_ind]);

    if (p_ble_gattc_evt->gatt_status == BLE_GATT_STATUS_SUCCESS)
    {
        // The descriptor was found at the peer.
        // Iterate through and collect CCCD, Extended Properties,
        // User Description & Report Reference descriptor handles.
        for (uint32_t i = 0; i < p_desc_disc_rsp_evt->count; i++)
        {
            switch (p_desc_disc_rsp_evt->descs[i].uuid.uuid)
            {
                case BLE_UUID_DESCRIPTOR_CLIENT_CHAR_CONFIG:
                    p_char_being_discovered->cccd_handle =
                        p_desc_disc_rsp_evt->descs[i].handle;
                    break;

                case BLE_UUID_DESCRIPTOR_CHAR_EXT_PROP:
                    p_char_being_discovered->ext_prop_handle =
                        p_desc_disc_rsp_evt->descs[i].handle;
                    break;

                case BLE_UUID_DESCRIPTOR_CHAR_USER_DESC:
                    p_char_being_discovered->user_desc_handle =
                        p_desc_disc_rsp_evt->descs[i].handle;
                    break;

                case BLE_UUID_REPORT_REF_DESCR:
                    p_char_being_discovered->report_ref_handle =
                        p_desc_disc_rsp_evt->descs[i].handle;
                    break;
            }

            /* Break if we've found all the descriptors we are looking for. */
            if (p_char_being_discovered->cccd_handle       != BLE_GATT_HANDLE_INVALID &&
                p_char_being_discovered->ext_prop_handle   != BLE_GATT_HANDLE_INVALID &&
                p_char_being_discovered->user_desc_handle  != BLE_GATT_HANDLE_INVALID &&
                p_char_being_discovered->report_ref_handle != BLE_GATT_HANDLE_INVALID)
            {
                break;
            }
        }
    }

    bool raise_discov_complete = false;

    if ((p_db_discovery->curr_char_ind + 1) == p_srv_being_discovered->char_count)
    {
        // No more characteristics and descriptors need to be discovered. Discovery is complete.
        // Send a discovery complete event to the user application.

        raise_discov_complete = true;
    }
    else
    {
        // Begin discovery of descriptors for the next characteristic.
        uint32_t err_code;

        p_db_discovery->curr_char_ind++;

        err_code = descriptors_discover(p_db_discovery,
                                        &raise_discov_complete,
                                        p_ble_gattc_evt->conn_handle);

        if (err_code != NRF_SUCCESS)
        {
            p_db_discovery->discovery_in_progress = false;

            // Error with discovering the service.
            // Indicate the error to the registered user application.
            discovery_error_evt_trigger(p_db_discovery, err_code, p_ble_gattc_evt->conn_handle);

            m_pending_user_evts[0].evt.evt_type    = BLE_DB_DISCOVERY_AVAILABLE;
            m_pending_user_evts[0].evt.conn_handle = p_ble_gattc_evt->conn_handle;

            return;
        }
    }

    if (raise_discov_complete)
    {
        NRF_LOG_DEBUG("Discovery of service with UUID 0x%x completed with success"
                      " on connection handle 0x%x.",
                      p_srv_being_discovered->srv_uuid.uuid,
                      p_ble_gattc_evt->conn_handle);

        discovery_complete_evt_trigger(p_db_discovery, true, p_ble_gattc_evt->conn_handle);
        on_srv_disc_completion(p_db_discovery, p_ble_gattc_evt->conn_handle);
    }
}


uint32_t ble_db_discovery_init(const ble_db_discovery_evt_handler_t evt_handler)
{
    uint32_t err_code = NRF_SUCCESS;
    VERIFY_PARAM_NOT_NULL(evt_handler);

    m_num_of_handlers_reg   = 0;
    m_initialized           = true;
    m_pending_usr_evt_index = 0;
    m_evt_handler           = evt_handler;

    return err_code;

}


uint32_t ble_db_discovery_close()
{
    m_num_of_handlers_reg   = 0;
    m_initialized           = false;
    m_pending_usr_evt_index = 0;

    return NRF_SUCCESS;
}


uint32_t ble_db_discovery_evt_register(ble_uuid_t const * p_uuid)
{
    VERIFY_PARAM_NOT_NULL(p_uuid);
    VERIFY_MODULE_INITIALIZED();

    return registered_handler_set(p_uuid, m_evt_handler);
}


static uint32_t discovery_start(ble_db_discovery_t * const p_db_discovery, uint16_t conn_handle)
{
    uint32_t err_code;
    ble_gatt_db_srv_t * p_srv_being_discovered;

    memset(p_db_discovery, 0x00, sizeof(ble_db_discovery_t));

    p_db_discovery->conn_handle = conn_handle;

    m_pending_usr_evt_index   = 0;

    p_db_discovery->discoveries_count = 0;
    p_db_discovery->curr_srv_ind      = 0;
    p_db_discovery->curr_char_ind     = 0;

    p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]);
    p_srv_being_discovered->srv_uuid = m_registered_handlers[p_db_discovery->curr_srv_ind];

    NRF_LOG_DEBUG("Starting discovery of service with UUID 0x%x on connection handle 0x%x.",
                  p_srv_being_discovered->srv_uuid.uuid, conn_handle);

    err_code = sd_ble_gattc_primary_services_discover(conn_handle,
                                                      SRV_DISC_START_HANDLE,
                                                      &(p_srv_being_discovered->srv_uuid));
    if (err_code != NRF_ERROR_BUSY)
    {
        VERIFY_SUCCESS(err_code);
        p_db_discovery->discovery_in_progress = true;
        p_db_discovery->discovery_pending     = false;
    }
    else
    {
        p_db_discovery->discovery_in_progress = true;
        p_db_discovery->discovery_pending     = true;
    }

    return NRF_SUCCESS;
}


uint32_t ble_db_discovery_start(ble_db_discovery_t * const p_db_discovery, uint16_t conn_handle)
{
    VERIFY_PARAM_NOT_NULL(p_db_discovery);
    VERIFY_MODULE_INITIALIZED();

    if (m_num_of_handlers_reg == 0)
    {
        // No user modules were registered. There are no services to discover.
        return NRF_ERROR_INVALID_STATE;
    }

    if (p_db_discovery->discovery_in_progress)
    {
        return NRF_ERROR_BUSY;
    }

    return discovery_start(p_db_discovery, conn_handle);
}


/**@brief     Function for handling disconnected event.
 *
 * @param[in] p_db_discovery    Pointer to the DB Discovery structure.
 * @param[in] p_ble_gattc_evt   Pointer to the GAP event.
 */
static void on_disconnected(ble_db_discovery_t       * p_db_discovery,
                            ble_gap_evt_t      const * p_evt)
{
    if (p_evt->conn_handle == p_db_discovery->conn_handle)
    {
        p_db_discovery->discovery_in_progress = false;
        p_db_discovery->discovery_pending     = false;
        p_db_discovery->conn_handle           = BLE_CONN_HANDLE_INVALID;
    }
}


void ble_db_discovery_on_ble_evt(ble_evt_t const * p_ble_evt,
                                 void            * p_context)
{
    VERIFY_PARAM_NOT_NULL_VOID(p_ble_evt);
    VERIFY_PARAM_NOT_NULL_VOID(p_context);
    VERIFY_MODULE_INITIALIZED_VOID();
    //NRF_LOG_INFO("In ble_discovery_evt function");
    ble_db_discovery_t * p_db_discovery = (ble_db_discovery_t *)p_context;

    switch (p_ble_evt->header.evt_id)
    {
        case BLE_GATTC_EVT_PRIM_SRVC_DISC_RSP:
        	NRF_LOG_INFO("Found services in.............");
            NRF_LOG_INFO("current discovery count:%d",p_db_discovery->discoveries_count);
            NRF_LOG_INFO("current service index: %d",p_db_discovery->curr_srv_ind);


            on_primary_srv_discovery_rsp(p_db_discovery, &(p_ble_evt->evt.gattc_evt));

            break;

        case BLE_GATTC_EVT_CHAR_DISC_RSP:
            on_characteristic_discovery_rsp(p_db_discovery, &(p_ble_evt->evt.gattc_evt));
            break;

        case BLE_GATTC_EVT_DESC_DISC_RSP:
            on_descriptor_discovery_rsp(p_db_discovery, &(p_ble_evt->evt.gattc_evt));
            break;

        case BLE_GAP_EVT_DISCONNECTED:
            on_disconnected(p_db_discovery, &(p_ble_evt->evt.gap_evt));
            break;

        default:
            break;
    }

    if (   (p_db_discovery->discovery_pending)
        && (p_ble_evt->header.evt_id >= BLE_GATTC_EVT_BASE)
        && (p_ble_evt->header.evt_id <= BLE_GATTC_EVT_LAST)
        && (p_ble_evt->evt.gattc_evt.conn_handle == p_db_discovery->conn_handle))
    {
        (void)discovery_start(p_db_discovery, p_db_discovery->conn_handle);
    }
}
#endif // NRF_MODULE_ENABLED(BLE_DB_DISCOVERY)

[Hung Bui]

Please make sure you check the status of the BLE_GATTC_EVT_PRIM_SRVC_DISC_RSP  event and it's SUCCESS not ATTRIBUTE_NOT_FOUND 

[Prajakta]

While checking service count in return argument is gives count=3. As services shown under that are total 4

[Hung Bui]

Then you need to continue calling sd_ble_gattc_primary_services_discover () until you receive ATTRIBUTE_NOT_FOUND  in the event BLE_GATTC_EVT_PRIM_SRVC_DISC_RSP  

[Prajakta]

I am able to discover all services.

I want to discover its characteristics and properties.

As you said i have added sd_ble_gattc_primary_services_discover (), and after that calling characteristics discover()  function but it fails. I think conn_hdle is same for both functions so this issue is coming. 
I am attaching code here.

1.Can you help to discover services along with its characteristics?

2. How to discover and print 128-bit UUID of unknown service.

Code as below:

void on_primary_srv_discovery_rsp(ble_db_discovery_t       * p_db_discovery,
                                         ble_gattc_evt_t    const * p_ble_gattc_evt)
{
    ble_gatt_db_srv_t * p_srv_being_discovered;
    uint16_t count = 0;

    uint16_t        bytes_to_copy;
    static uint16_t offset = 0;
    int conn_hdle;
	conn_hdle = p_ble_gattc_evt->conn_handle;


    ble_gattc_service_t * const p_service =
            		mp_device_srv[conn_hdle]->services;

    p_srv_being_discovered = &(p_db_discovery->services[p_db_discovery->curr_srv_ind]);

    if (p_ble_gattc_evt->conn_handle != p_db_discovery->conn_handle)
    {
   // 	return;
    }

    if (p_ble_gattc_evt->gatt_status == BLE_GATT_STATUS_SUCCESS)
    {

    	//int i = 0;
    	ble_gattc_evt_prim_srvc_disc_rsp_t const * p_prim_srvc_disc_rsp_evt;
        uint32_t err_code;

        p_prim_srvc_disc_rsp_evt = &(p_ble_gattc_evt->params.prim_srvc_disc_rsp);
        count = p_prim_srvc_disc_rsp_evt->count;
        NRF_LOG_INFO("service count %d",count);

		// If no more services are found.
		if ((count != 0) &&
		(p_ble_gattc_evt->gatt_status == BLE_GATT_STATUS_SUCCESS))
		{
			if ((count + offset) > MAX_SERVICE_COUNT)
			{
				bytes_to_copy = MAX_SERVICE_COUNT - offset;
			}
			else
			{
				bytes_to_copy = count;
			}

			// Save services data.
			memcpy((p_service + offset),p_prim_srvc_disc_rsp_evt->services,
			bytes_to_copy * sizeof(ble_gattc_service_t));

			offset += count;
			for(int i= 0;i <= count; i++ )
			{
			p_srv_being_discovered->srv_uuid     = p_prim_srvc_disc_rsp_evt->services[i].uuid;
			p_srv_being_discovered->handle_range = p_prim_srvc_disc_rsp_evt->services[i].handle_range;

			NRF_LOG_INFO("Found service UUID %x and its start handle:%d , End handle: %d", p_srv_being_discovered->srv_uuid.uuid,
			p_srv_being_discovered->handle_range.start_handle, p_srv_being_discovered->handle_range.end_handle);
			}
			// If the last service has not been reached, this function must be called again with a new start handle.
			err_code = sd_ble_gattc_primary_services_discover(conn_hdle,
			p_prim_srvc_disc_rsp_evt->services[count - 1].handle_range.end_handle + 1,
			NULL);
			if(err_code == NRF_SUCCESS)
			{
			NRF_LOG_INFO("Discovery done successfully..");
			}
			else
			{
			NRF_LOG_INFO("Discovery Fail..");

			}
		//  APP_ERROR_CHECK(err_code);
		}

        err_code = characteristics_discover(p_db_discovery, p_ble_gattc_evt->conn_handle);

        if (err_code != NRF_SUCCESS)
        {
            p_db_discovery->discovery_in_progress = false;

            NRF_LOG_INFO("Error with discovering the characteristics");
            // Indicate the error to the registered user application.
            discovery_error_evt_trigger(p_db_discovery, err_code, p_ble_gattc_evt->conn_handle);

            m_pending_user_evts[0].evt.evt_type    = BLE_DB_DISCOVERY_AVAILABLE;
            m_pending_user_evts[0].evt.conn_handle = p_ble_gattc_evt->conn_handle;
        }
    }
    else
    {
        NRF_LOG_INFO("Service UUID 0x%x not found.", p_srv_being_discovered->srv_uuid.uuid);
        // Trigger Service Not Found event to the application.
        discovery_complete_evt_trigger(p_db_discovery, false, p_ble_gattc_evt->conn_handle);
        on_srv_disc_completion(p_db_discovery, p_ble_gattc_evt->conn_handle);
    }
    NRF_LOG_INFO("Services count at end: %d", offset);
     offset = 0;
}

[Prajakta]

I am able to discover 4 services. But last service which is custom and having 128-bit UUID, its start handle and end handle = 0.
So not able to discover characteristics.
Output as below:

<info> ble_db_disc: Found service UUID 1800 and its start handle:1 , End handle: 7
<info> ble_db_disc: Found service UUID 1801 and its start handle:8 , End handle: 11
<info> ble_db_disc: Found service UUID 180A and its start handle:12 , End handle: 20
<info> ble_db_disc: Found service UUID 5D4 and its start handle:0 , End handle: 0