NRF52 discovery event has all characteristic uuids 0

[Chang.tsai]

I have trouble developing BLE devices with Nordic NRF5280 and SDK 15.3.

I have a device that uses a custom BLE service, And when using nRF Connect on the mobile phone, all BLE services and characteristic values can be listed.

But when using a central NRF52840 on SDK 15.3, the characteristic value UUID returned by the db discovery event BLE_GATTC_EVT_CHAR_DISC_RSP event is all 0.

This is the screen on the phone, and 0xF6D6 is the customized BLE service UUID.

I set BLE_GATT_DB_MAX_CHARS to 14, because I know there are 13 characteristic values of the Bluetooth service to be read.

I started to explore the custom BLE service (0xFD6D) in the BLE_GAP_EVT_CONNECTED event.

Fullscreen ble_service_discovery.c Download

ret_code_t app_ble_db_discovery_start(app_ble_db_disc_t * pDisc)
{
    // Initialize the service discovery database
    ret_code_t err_code = ble_db_discovery_init(app_db_disc_handler);
    if (err_code != NRF_SUCCESS)
    {
        APP_DISC_INFO("ble_db_discovery_init(), err = %s." , nrf_strerror_get(err_code));
        return err_code;
    }

    // Register the UUIDs to be explored in order
    for (uint8_t i = 0; i < pDisc->count; i++)
    {
        err_code = ble_db_discovery_evt_register(&pDisc->uuid[i]);
        if (err_code != NRF_SUCCESS)
        {
            APP_DISC_ERR("ble_db_discovery_evt_register(), uuid[%d], err = 0x04X", i, err_code);
        }
        else
            APP_DISC_INFO("ble_db_discovery_evt_register(), uuid[%d]: 0x%04X", i, pDisc->uuid[i].uuid);
    }

    // Save the function handles for processing search events and the total number of services that started exploration
    m_service_count = pDisc->count;
    APP_DISC_INFO("db discovery start, service count = %d.", m_service_count);

    // Start service exploration, and return whether the startup is successful
    memset(&m_db_disc, 0x00, sizeof(m_db_disc));
    err_code = ble_db_discovery_start(&m_db_disc, pDisc->conn_handle);
    if (err_code != NRF_SUCCESS)
    {
        APP_DISC_INFO("ble_db_discovery_start(), conn_handle = 0x%04X, err = %s." , pDisc->conn_handle, nrf_strerror_get(err_code));
    }

    return err_code;
}

I inserted a debug message in the function on_characteristic_discovery_rsp() in ble_db_discovery.c.

The modified code is as follows:

Fullscreen debug.c Download

/**@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_WARNING("%s(): Update the characteristics count = %d.", __FUNCTION__, p_srv_being_discovered->char_count)
        }
        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_WARNING("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++)
        {
            NRF_LOG_WARNING("%s (): char[%d] UUID: 0x%04X.", __FUNCTION__, i, p_ble_gattc_evt->params.char_disc_rsp.chars[j].uuid.uuid);
            p_srv_being_discovered->charateristics[i].characteristic =
                p_char_disc_rsp_evt->chars[j];

            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);
        }
    }
}

When i run this, The Debug message by using NRF_LOG_WARNING("%s (): char[%d] UUID: 0x%04X.", __FUNCTION__, i, p_ble_gattc_evt->params.char_disc_rsp.chars[j].uuid.uuid) is as follows:

Fullscreen NRF52840 debug.txt Download

-------------------------------------------------------------------------------------------------------
<info> ble_s: ble_evt_handler(): BLE Connected role: Central, handle 0x0.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 1.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[0] UUID: 0x0000.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 2.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[1] UUID: 0x0000.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 3.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[2] UUID: 0x0000.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 4.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[3] UUID: 0x0000.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 5.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[4] UUID: 0x0000.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 6.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[5] UUID: 0x0000.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 7.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[6] UUID: 0x0000.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 8.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[7] UUID: 0x0000.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 9.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[8] UUID: 0x0000.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 10.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[9] UUID: 0x0000.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 11.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[10] UUID: 0x0000.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 12.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[11] UUID: 0x0000.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 13.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[12] UUID: 0x0000.
<info> APP_DISC: app_db_disc_handler(): BLE on db disc for peripheral, handle: 0x0000.


-------------------------------------------------------------------------------------------------------
<info> APP_DISC: app_db_disc_handler(): Service UUID[1]: 0xFD6D disc complete(0)
<info> ble_c: ble_on_db_disc_evt(): discovery complete, Use service index: 2.
<info> ble_c: ble_on_db_disc_evt(): num of characteristic: 13.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x0000.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x0000.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x0000.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x0000.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x0000.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x0000.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x0000.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x0000.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x0000.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x0000.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x0000.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x0000.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x0000.
<info> ble_c: ble_on_db_disc_evt():  Service discovered at peer.
<info> ble_c: ble_on_db_disc_evt():  Service handle address: 0x0007A4E5, index = 0.

In addition, I also tried to search for other customized services (0x18EF), and the characteristics of the 0x18EF service are listed correctly.

Fullscreen NRF52840 debug_0x18EF.txt Download

-------------------------------------------------------------------------------------------------------
<info> ble_s: ble_evt_handler(): BLE Connected role: Central, handle 0x0.
<info> ble_s: gatt_evt_handler(): ATT MTU updated to 23 bytes on connection 0x0 (response).
<info> ble_s: gatt_evt_handler(): DLE:Data length updated to 27 on connection 0x0.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 1.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[0] UUID: 0x2AC0.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 2.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[1] UUID: 0x2AC1.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 3.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[2] UUID: 0x2AC2.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 4.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[3] UUID: 0x2AC3.
<warning> ble_db_disc: on_characteristic_discovery_rsp(): Update the characteristics count = 5.
<warning> ble_db_disc: on_characteristic_discovery_rsp (): char[4] UUID: 0x2AC4.
<info> APP_DISC: app_db_disc_handler(): BLE on db disc for peripheral, handle: 0x0000.


-------------------------------------------------------------------------------------------------------
<info> APP_DISC: app_db_disc_handler(): Service UUID[2]: 0x18EF disc complete(0)
<info> ble_c: ble_on_db_disc_evt(): discovery complete, Use service index: 0.
<info> ble_c: ble_on_db_disc_evt(): num of characteristic: 5.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x2AC0.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x2AC1.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x2AC2.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x2AC3.
<info> ble_c: ble_on_db_disc_evt():   Characteristic Uuid: 0x2AC4.
<info> ble_c: ble_on_db_disc_evt(): Service discovered at peer.
<info> ble_c: ble_on_db_disc_evt(): Service handle address: 0x0007A4E5, index = 0.

My question is why NRF52840 can't get the characteristic value UUID of Bluetooth service 0xFD6D like nRF Connect on mobile phone?

please help me.

[Chang.tsai]

I have conducted various tests for this issue these days.

I noticed that the customized UUID of this device is 0000fd6d-0000-1000-8000-00805f9b34fb.

Looks like the Bluetooth SIG basic UUID, Not sure if this is the cause of the problem...

Will SoftDevice treat the Bluetooth SIG basic UUID differently from the general custom UUID?

[Joakim Jakobsen]

Hi. 

Sorry about the delayed response. I don't think the SD will tread the custom UUID differently, but I'll ask internally in our SD team and get back to you. 

Br, 
Joakim

[Joakim Jakobsen]

Hi again.

Maybe you could add some code snippets for how you add the characteristics and the UUIDs?

Also, you might be able to find some relevant information from previous tickets. Like this one:
https://devzone.nordicsemi.com/f/nordic-q-a/40578/discovering-a-vs-uuid-characterisic-but-it-shows-uuid-as-0

Br,
Joakim

[Chang.tsai]

Thank you for the information, I have solved this problem.

According to the ticket you provided, I found the cause of the problem. The cause of this problem is that the basic UUID of the BLE service is different from the basic UUID of the characteristic.

When I used sd_ble_uuid_vs_add() to add a custom UUID before, only the UUID of the service was added, and the UUID of the characteristic was not added.

Now I use sd_ble_uuid_vs_add() to add the UUID of the characteristic to the custom UUID, and everything is good.

[Joakim Jakobsen]

Thanks for sharing. 

Br, 
Joakim