Not able to receive handles of custom service characteristics in central device

RE: Not able to receive handles of custom service characteristics in central device

Edvin — Mon, 03 Aug 2020 13:09:56 GMT

Hello,

Sorry for the late reply. I was out of office the last 14 days due to vacation.

If you are still struggling with this:

I don't know what your implementation looks like. If you look at the implementation from the ble_app_uart_c example:

void ble_nus_c_on_db_disc_evt(ble_nus_c_t * p_ble_nus_c, ble_db_discovery_evt_t * p_evt)
{
    ble_nus_c_evt_t nus_c_evt;
    memset(&nus_c_evt,0,sizeof(ble_nus_c_evt_t));

    ble_gatt_db_char_t * p_chars = p_evt->params.discovered_db.charateristics;

    // Check if the NUS was discovered.
    if (    (p_evt->evt_type == BLE_DB_DISCOVERY_COMPLETE)
        &&  (p_evt->params.discovered_db.srv_uuid.uuid == BLE_UUID_NUS_SERVICE)
        &&  (p_evt->params.discovered_db.srv_uuid.type == p_ble_nus_c->uuid_type))
    {
        for (uint32_t i = 0; i < p_evt->params.discovered_db.char_count; i++)
        {
            switch (p_chars[i].characteristic.uuid.uuid)
            {
                case BLE_UUID_NUS_RX_CHARACTERISTIC:
                    nus_c_evt.handles.nus_rx_handle = p_chars[i].characteristic.handle_value;
                    break;

                case BLE_UUID_NUS_TX_CHARACTERISTIC:
                    nus_c_evt.handles.nus_tx_handle = p_chars[i].characteristic.handle_value;
                    nus_c_evt.handles.nus_tx_cccd_handle = p_chars[i].cccd_handle;
                    break;

                default:
                    break;
            }
        }
        if (p_ble_nus_c->evt_handler != NULL)
        {
            nus_c_evt.conn_handle = p_evt->conn_handle;
            nus_c_evt.evt_type    = BLE_NUS_C_EVT_DISCOVERY_COMPLETE;
            p_ble_nus_c->evt_handler(p_ble_nus_c, &nus_c_evt);
        }
    }
}

You see that it checks a few things before it looks at the uuids:

if ( (p_evt->evt_type == BLE_DB_DISCOVERY_COMPLETE)
&& (p_evt->params.discovered_db.srv_uuid.uuid == BLE_UUID_NUS_SERVICE)
&& (p_evt->params.discovered_db.srv_uuid.type == p_ble_nus_c->uuid_type))

Do you do the same check? Perhaps it is not a BLE_DB_DISCOVERY_COMPLETE event at all, in which case the uuids would not be populated.

BR,

Edvin

RE: Not able to receive handles of custom service characteristics in central device

Abhishek — Tue, 21 Jul 2020 06:40:32 GMT

Hi Edvin

I was checking ble_nus_c_evt_handler for same function which you mentioned and i checked the pointer in watch window for all p_chars[], but all uuid were 0x00.

As my custom characteristic foot print is similar to nRF LBS service modified ble_app_blinky_c example to suit my needs and now it is working. How ever i am not sure what went wrong with ble_app_uart_c project modification.

Thanks

RE: Not able to receive handles of custom service characteristics in central device

Edvin — Wed, 15 Jul 2020 15:18:34 GMT

I believe that the ble_app_uart_c is a good reference project to discover services and characteristics.

[quote user=""]Now in code I am connected to device during db_discovery i am getting to the configured callback function but i am not getting characteristics of the peripheral. [/quote]

Is that the ble_nus_c_evt_handler with the evt_type = BLE_NUC_C_EVT_DISCOVERY_COMPLETE, or the ble_nus_c_on_db_disc_evt() in ble_nus_c.c? Or somewhere else?

If it is the ble_nus_c_on_db_disc_evt(). Look at the unmodified implementation of ble_nus_c.c. What is the p_chars[i].characteristic.uuid.uuid? Is it the UUID that you expect? (Note that this callback may occur several times if the device has several services, so make sure you are checking the correct event, when p_evt->params.discovered_db.srv.uuid is the one that you expect.

BR,
Edvin