Custom UART BLE Read fails

[Lodge]

Hello, I have a custom program based on the uart example. I can write to the device, but sending to the master fails. I call the SendString code, but p_nus->is_notification_enabled is always false. Looking through the code, the only place this flag gets set true is in:

static void on_write(ble_nus_t * p_nus, ble_evt_t * p_ble_evt)
{
    ble_gatts_evt_write_t * p_evt_write = &p_ble_evt->evt.gatts_evt.params.write;
    if ((p_evt_write->handle == p_nus->rx_handles.cccd_handle)  && (p_evt_write->len == 2))
    {
        if (ble_srv_is_notification_enabled(p_evt_write->data))
        {
            p_nus->is_notification_enabled = true;
        }
        else
        {
            p_nus->is_notification_enabled = false;
        }
    }
    else if ((p_evt_write->handle == p_nus->tx_handles.value_handle) && (p_nus->data_handler != NULL))
    {
        p_nus->data_handler(p_nus, p_evt_write->data, p_evt_write->len);
    }
    else
    {
        // Do Nothing. This event is not relevant for this service.
    }

Can anyone explain where the message with p_evt_write->handle == p_nus->rx_handles.cccd_handle and with a length of 2 comes from? If this part of the code is never called, then i cant send any data to the master. Much appreciated.

[Alex]

That part of the code called when you enable notification from master. For example in Master Control Panel in Android connect to your device, choose service and then on right hand side of characteristic you will see three down arrows. Press on them and notification will be enabled. If you are using your own application then you need to enable notification in your application before the first SendString used in the device

[Alex]

Short and nice explanation is here