BLE Central not getting a scan response message from a sensor

[DavidKaplan]

Shalom!

 Our central BLE nrf52840 device continuously scans using a UUID filter. I can see that the UUID is matched in nrf_ble_scan_on_adv_report().  In my ble_evt_handler's BLE_GAP_EVT_ADV_REPORT, I see all BLE devices in the central's range not only my sensor which is OK. I keep a list of the sensors with the filtered UUID and their RSSIs from their advertisements. I can select a MAC and connect to the device from the list without problems.

Now the company want to select a sensor according to its name which is sent in its scan response during he installation process.

I understand that I should be getting two events, one with the p_adv_report->type.scan_response flag raised. The flag is never raised.

Only for product installation, I would like to initiate a scan requests for the sensors, otherwise I would just like to sniff their advertisements.

static ble_gap_scan_params_t const m_scan_param =
{
    .active        = 0x01,
#if (NRF_SD_BLE_API_VERSION > 7)
    .interval_us   = NRF_BLE_SCAN_SCAN_INTERVAL * UNIT_0_625_MS,
    .window_us     = NRF_BLE_SCAN_SCAN_WINDOW * UNIT_0_625_MS,
#else
    .interval      = NRF_BLE_SCAN_SCAN_INTERVAL,
    .window        = NRF_BLE_SCAN_SCAN_WINDOW,
#endif // (NRF_SD_BLE_API_VERSION > 7)
    .filter_policy = BLE_GAP_SCAN_FP_WHITELIST,
    .timeout       = SCAN_DURATION_WITELIST,
    .scan_phys     = BLE_GAP_PHY_1MBPS,
};

/**@brief Function for initializing the scanning and setting the filters.
 */
static void scan_init(bool connect_if_matc)
{
    char sBuf[32];
    ret_code_t          err_code;
    nrf_ble_scan_init_t init_scan;

    memset(&init_scan, 0, sizeof(init_scan));
    init_scan.connect_if_match = connect_if_matc;
    init_scan.conn_cfg_tag     = APP_BLE_CONN_CFG_TAG;
#ifdef USE_PM
    init_scan.p_scan_param     = &m_scan_param;
#endif

    err_code = nrf_ble_scan_init(&m_scan, &init_scan, scan_evt_handler);
    APP_ERROR_CHECK(err_code);
    //-------------------------------------------------------------------------
    // Remove any filters previously set
    //-------------------------------------------------------------------------
    err_code = nrf_ble_scan_all_filter_remove(&m_scan);
    APP_ERROR_CHECK(err_code);


    err_code = nrf_ble_scan_filter_set(&m_scan, SCAN_UUID_FILTER, &m_ami_uuid);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_ble_scan_filters_enable(&m_scan, NRF_BLE_SCAN_UUID_FILTER, true);
    APP_ERROR_CHECK(err_code);
} // scan_init

How can I case a scan request to be sent?

Thank you

David Kaplan

[Vidar Berg]

Hello,

Is the UUID which you are filtering on placed in the adv. packet or in the scan response packet? It looks like .connect_if_match is enabled, so I would expect it to just send a connect request instead of a scan request if you're getting a filter match on the main adv. packet.

I don't see anything else that's wrong. Maybe you have already, but you can also use the configuration from the ble_app_uart_c example as a reference as it should be similiar to yours (active scanner + uuid filter)

Best regards,

Vidar

[DavidKaplan]

Shalom!

Thanks for your swift reply.

I used the app_uart_c example as my base program with the sensors base 128 bit UUID.

I see that the connect_if_match is disabled and the WireShark sniffing does not show a connection but it does show a scan request and a scan response from the sensor. I am not seeing the response in my event handler's BLE_GAP_EVT_ADV_REPORT as the p_adv_report->type.scan_response flag is never raised. When I want to connect I also set the MAC filter since we may have several sensors and raise the connect_if_match and it does connect.

Again, most of the time I only want to sniff all sensors updating their RSSIs and want no scan request. In the installation process, I need to get the sensor's name from the scan response and associate it with the sensor's MAC.

In the BLE_GAP_EVT_ADV_REPORT event I see all kinds of sensors and not just the type for this project. The central is continuously scanning until a connection is warranted to pull or push data.

I do not currently use a whitelist or encryption.

#define BLE_UUID_AMI_SERVICE                   0x0101
       
uint32_t p_ble_maint_c_init(ble_maint_c_t * p_ble_maint_c, ble_maint_c_init_t * p_ble_maint_c_init)
{
    uint32_t      err_code;
    ble_uuid_t    uart_uuid;
    ble_uuid128_t nus_base_uuid = AMI_BASE_UUID;

    VERIFY_PARAM_NOT_NULL(p_ble_maint_c);
    VERIFY_PARAM_NOT_NULL(p_ble_maint_c_init);
    VERIFY_PARAM_NOT_NULL(p_ble_maint_c_init->p_gatt_queue);

    err_code = sd_ble_uuid_vs_add(&nus_base_uuid, &p_ble_maint_c->uuid_type);
    VERIFY_SUCCESS(err_code);

    uart_uuid.type = p_ble_maint_c->uuid_type;
    uart_uuid.uuid = BLE_UUID_AMI_SERVICE;

    p_ble_maint_c->conn_handle           = BLE_CONN_HANDLE_INVALID;
    p_ble_maint_c->evt_handler           = p_ble_maint_c_init->evt_handler;
    p_ble_maint_c->error_handler         = p_ble_maint_c_init->error_handler;
    p_ble_maint_c->p_gatt_queue          = p_ble_maint_c_init->p_gatt_queue;

    memset(p_ble_maint_c->maint_db.bl_handle,BLE_GATT_HANDLE_INVALID,sizeof(p_ble_maint_c->maint_db.bl_handle));
    memset(p_ble_maint_c->maint_db.cccd_handle,BLE_GATT_HANDLE_INVALID,sizeof(p_ble_maint_c->maint_db.cccd_handle));
    return ble_db_discovery_evt_register(&uart_uuid);
} // p_ble_maint_c_init

Any tips to understand what is happening?

Thanks

David Kaplan

[DavidKaplan]

Shalom!

 I am ashamed to say that I found my problem.

I was filtering the advertisements in the adv_report by my sensor type's message length, to reduce CPU time, then going on to check if the advertisement was with my BLE sensor's UUID.

The sensor's scan response is not the same length as its advertisement so I missed it.

Many Thanks.

At least I learned a little better about how things work from this incident.

[Vidar Berg]

Thanks for the update!