Triggering event handler upon CCCD for notifications change

[Tosa]

In the ble_nus service (SDK11.0.0 S132 nRF52), what is the simplest way to modify on_write() to send inform the main application the CCCD for notifications has changed:

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.
}}

Currently just the is_notification_enabled field is set, but the event handler is not triggered in the application level, so the application will not be informed or know that some data in p_nus has been modified.

[Tosa]

I think I confused you by saying "main application". What I mean is that I want the event handler p_nus->data_handler() to be called with some information stating that the CCCD has changed. What is the simplest way to do this?

[Susheel Nuguru]

in that case just add one more variable in ble_nus_t

bool cccd_changed;

and on write

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;
    }
    p_nus->cccd_changed = true;
    p_nus->data_handler(p_nus, p_evt_write->data, p_evt_write->len);
}
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.
}}


static void nus_data_handler(ble_nus_t * p_nus, uint8_t * p_data, uint16_t length)
{
  if(p_nus->cccd_changed)
   {
     p_nus->cccd_changed = false;
     // do your processing here
   }
   
   ....
   ....
}