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

[Abhishek]

I am working in nRF52840 chip with SDK 15.3.0 and softdevice s140. I am looking to automate third party BLE peripheral device, this device is designed to connect with smart phone and then smartphone is communicating with server through internet. I am looking to eliminate smartphone by replacing it with custom central and ESP8266 module. I am able to use the peripheral through nRF Connect mobile app.

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. 

I am modifying ble_app_uart_c example from sdk. Please suggest the correct sample project which is using custom services to refer and modify according to my example.

Thanks.

[Edvin]

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

 

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. 

 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

[Abhishek]

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

[Edvin]

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