Where is the proper place to close a connection when a service is not discovered

[David Andresky]

Hi, I am developing a central device application using the ble_app_multirole_lesc example as a baseline. I am using v11 of the SDK. This example uses the heart rate service as a demonstration on how to connect, discover services, characteristics, etc. and receive updates.

So far in my application I have removed all peripheral mode functionality and I have added a filter for the advertisements so that I only attempt connections with my peripheral device. At this point the central device will successfully connect to my sensor. It then attempts to discover the HRS and RSCS services which will fail as I have a custom service on my device. The problem is that the central device does not release the connection after failing to find the heart rate services. It will maintain the connection forever if I don't reset one of the two devices.

After some investigation, I have found that the on_srv_disc_completion function in the ble_db_discovery.c code module seems to be the best place to close the connection. Below code snippet shows the three lines of code I added to close the connection:

else
{
    NRF_LOG_PRINTF("Inside the on_srv_disc_completion function - no more discovery needed\r\n");

    // No more service discovery is needed.
    p_db_discovery->discovery_in_progress = false;
    m_pending_user_evts[0].evt.evt_type = BLE_DB_DISCOVERY_AVAILABLE;
    m_pending_user_evts[0].evt.conn_handle = conn_handle;
    //m_evt_handler(&m_pending_user_evts[0].evt);

   err_code = sd_ble_gap_disconnect(conn_handle, BLE_HCI_REMOTE_USER_TERMINATED_CONNECTION);
   APP_ERROR_CHECK(err_code);
}

I also discovered the connection could be closed in the ble_hrs_on_db_disc_evt of the ble_hrs_c.c code module but it seems the function above will still execute before the connection is closed so I moved it there.

My question is where is the best place to close the connection when a desired service is not discovered? It seems I should not have to change files in the SDK to make this happen. I expected there to be an event I could register for in my application and handle it there but I can't see what that is.

[Susheel Nuguru]

Hi,

Calling disconnect unconditionally in the on_srv_disc_completion will make the calling device disconnect even if discovered your service. 

I would add a boolean, which is initialized to false and set to true when you found the service. Then fence the disconnect call with the logic of this boolean.

if(false == service_found)
{
   err_code = sd_ble_gap_disconnect(conn_handle, BLE_HCI_REMOTE_USER_TERMINATED_CONNECTION);
   APP_ERROR_CHECK(err_code);
}

And to answer your question, with this small change,  placing disconnect in on_srv_disc_completion looks good.

[David Andresky]

Thanks, I want to avoid editing SDK files. I ended up adding it to the ble_pss_on_db_disc_evt in my client code module so that if I fail to discover the desired UUID then I will close the connection. I also added to the BLE_GATTC_EVT_READ_RSP after read an attribute. This seems to satisfy my needs for now.

[Susheel Nuguru]

that is also a good way to do it. thanks for updating us on one additional way to do it.