Purpose of on_connect function in ble_nus.c?

[riceman0]

Hello, I am studying the peripheral/ble_app_uart and peripheral/ble_app/template examples to understand the proper way to build a peripheral with our own set of services and characteristics.  I'm also studying this tutorial:

https://devzone.nordicsemi.com/nordic/short-range-guides/b/bluetooth-low-energy/posts/ble-services-a-beginners-tutorial

One thing I don't understand is the purpose of the on_connect function in ble_nus.  It says that it is checking 'the hosts CCCD value to inform of readiness to send data using the RX characteristic' and then it is performing a sd_ble_gatts_value_get.  I don't really understand the purpose of these two things, and it's not explained in the tutorial.  Do I need to do something like this when setting up my own characteristics?  

Thanks!

/**@brief Function for handling the @ref BLE_GAP_EVT_CONNECTED event from the SoftDevice.
 *
 * @param[in] p_nus     Nordic UART Service structure.
 * @param[in] p_ble_evt Pointer to the event received from BLE stack.
 */
static void on_connect(ble_nus_t * p_nus, ble_evt_t const * p_ble_evt)
{
    ret_code_t                 err_code;
    ble_nus_evt_t              evt;
    ble_gatts_value_t          gatts_val;
    uint8_t                    cccd_value[2];
    ble_nus_client_context_t * p_client = NULL;

    err_code = blcm_link_ctx_get(p_nus->p_link_ctx_storage,
                                 p_ble_evt->evt.gap_evt.conn_handle,
                                 (void *) &p_client);
    if (err_code != NRF_SUCCESS)
    {
        NRF_LOG_ERROR("Link context for 0x%02X connection handle could not be fetched.",
                      p_ble_evt->evt.gap_evt.conn_handle);
    }

    /* Check the hosts CCCD value to inform of readiness to send data using the RX characteristic */
    memset(&gatts_val, 0, sizeof(ble_gatts_value_t));
    gatts_val.p_value = cccd_value;
    gatts_val.len     = sizeof(cccd_value);
    gatts_val.offset  = 0;

    err_code = sd_ble_gatts_value_get(p_ble_evt->evt.gap_evt.conn_handle,
                                      p_nus->tx_handles.cccd_handle,
                                      &gatts_val);

    if ((err_code == NRF_SUCCESS)     &&
        (p_nus->data_handler != NULL) &&
        ble_srv_is_notification_enabled(gatts_val.p_value))
    {
        if (p_client != NULL)
        {
            p_client->is_notification_enabled = true;
        }

        memset(&evt, 0, sizeof(ble_nus_evt_t));
        evt.type        = BLE_NUS_EVT_COMM_STARTED;
        evt.p_nus       = p_nus;
        evt.conn_handle = p_ble_evt->evt.gap_evt.conn_handle;
        evt.p_link_ctx  = p_client;

        p_nus->data_handler(&evt);
    }
}

[Simonr]

Hi

The on_connect function is there to handle the BLE_GAP_EVT_CONNECTED event from the SoftDevice when the ble_nus_on_ble_evt() function is called. When using other services than NUS, this function is called from ble_conn_params.c, so it should be handled by the SDK when creating your own characteristics as well.

You can check out the ble_custom_service example over at our GitHub for a more complete tutorial on how to set up custom services and characteristics here.

Best regards,

Simon

[riceman0]

thanks!