MAC Address BLE scan filter not working

[Daniela_A]

Hello all,

Currently I am developing a code in which a central (nRF52840) scans and reads adverisement packets from 2 beacons (no connection required). I decided to use an adress filter to limit the amount of advertisement data received; however, it seems that it is not working because:
1. I´m getting TONS of advertisement packets that don´t look similar to what I´m expecting.
2. The event NRF_BLE_SCAN_EVT_FILTER_MATCH is never triggered.

Below I´ll show you some key points of the code: 

Declarition of the target MAC address (AC:23:3F:A9:EF:E2)

static bool is_connect_per_addr = true;            /**< If you want to connect to a peripheral with a given address, set this to true and put the correct address in the variable below. */

static ble_gap_addr_t const m_target_periph_addr =
{
    /* Possible values for addr_type:
       BLE_GAP_ADDR_TYPE_PUBLIC,
       BLE_GAP_ADDR_TYPE_RANDOM_STATIC,
       BLE_GAP_ADDR_TYPE_RANDOM_PRIVATE_RESOLVABLE,
       BLE_GAP_ADDR_TYPE_RANDOM_PRIVATE_NON_RESOLVABLE. */
    //.addr_type = BLE_GAP_ADDR_TYPE_RANDOM_STATIC,
    .addr      = {0xE2, 0xEF, 0xA9, 0x3F, 0x23, 0xAC}
    //.addr      = {0x41, 0x8C, 0xFE, 0x05, 0x1C, 0x00}
};

Filters settings

static void scan_init(void)
{
    ret_code_t          err_code;
    nrf_ble_scan_init_t init_scan;

    //static char const test_periph_addr[] = {0xEA, 0xEF, 0xA9, 0x3F, 0x23, 0xAC};

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

    init_scan.p_scan_param     = &m_scan_param;
    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);

    ble_uuid_t uuid =
    {
        .uuid = TARGET_UUID,
        .type = BLE_UUID_TYPE_VENDOR_BEGIN,
    };

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

    if (strlen(m_target_periph_name) != 0)
    {
        err_code = nrf_ble_scan_filter_set(&m_scan,
                                           SCAN_NAME_FILTER,
                                           m_target_periph_name);
        APP_ERROR_CHECK(err_code);
    }

    if (is_connect_per_addr)
    {
       err_code = nrf_ble_scan_filter_set(&m_scan,
                                          SCAN_ADDR_FILTER,
                                          m_target_periph_addr.addr);
       APP_ERROR_CHECK(err_code);
    }

    err_code = nrf_ble_scan_filters_enable(&m_scan,
                                           NRF_BLE_SCAN_ALL_FILTER,
                                           false);
    APP_ERROR_CHECK(err_code);
}

ADV_REPORT EVENT

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_ADV_REPORT:
            NRF_LOG_INFO("Advertisement report");
            //on_adv_report(&p_gap_evt->params.adv_report);

            //if( p_gap_evt->params.adv_report.direct_addr.addr == m_target_periph_addr.addr)
            //{    
            //    NRF_LOG_INFO("Found");
            //}

           
            uint8_t data_length = p_gap_evt->params.adv_report.data.len;
            NRF_LOG_INFO("Data length: %d", data_length);

            uint8_t i;

            for (i=0; i<=data_length; i++)
            {
                uint8_t data = p_gap_evt->params.adv_report.data.p_data[i];
                NRF_LOG_INFO("0x%02X", data);
            }

            break;

...

Thank you so much in advance

[Daniela_A]

Hello Vidar and thank you for your answers.

Now I have some more quesions:

1. How do you know that the device might be using a  private resolvable address? (I´m curious and I will like to earn to identify tem as well)
2. Is this address the same as the MAC address of the device?
   

Thank you

PS: Thanks on your comments about the ADV_REPORT event

[Vidar Berg]

Hello,

No problem The address type is included in the adv. report event (adv_report->peer_addr.addr_type). The actual mac address is not included in the advertisment when a private address is used. It's typically only exchanged during bonding.

Best regards,

Vidar

[Daniela_A]

Hello Vidar,

I am a bit confused right now, because you said that "The actual mac address is not included in the advertisment when a private address is used"; however, this is what I see when I scan the device with nRFConnect mobile app

As you can see, the MAC address is present in the advertisement packet. What is happening, then?

[Vidar Berg]

Hello,

They are actually using a public address type. I looked it up here: https://hwaddress.com/oui-iab/AC-23-3F/.  Unlike the other address types, it's not possible to tell if an address is public just by looking at the MSB bits , which means you have to get the address type from the adv. report event.

I'm not sure why they have duplicated the address in the Manufacturer data field.

[Daniela_A]

Hello,

Taking into account that the address is public, would it possible for me to use to MAC Address filter to find the device? 

Thanks

[Vidar Berg]

Hello,

Yes, a public address will not change like a private address would.