Mismatch between connection handles in ble_nus?

Question

I'm using the nus_c service with multiple central connections. Obviously, I need the connection handle in my event handler - ble_nus_c_evt_handler(ble_nus_c_t* p_ble_nus_c, const ble_nus_c_evt_t* p_ble_nus_evt) . 
 I've noticed that when BLE_NUS_C_EVT_NUS_RX_EVT is raised, the connection handle in the NUS context object and the event object are different: p_ble_nus_c->conn_handle == 1 , as expected, while p_ble_nus_evt->conn_handle == 0 . 
 I've traced it down to on_hvx() in ble_nus_c.c, not setting the connection handle from the GATTC event to the ble_nus_c_evt_t structure it dispatches. 
 Is this by design or a bug?

Sigurd · Accepted Answer

Hi, 
 Yes, the on_hvx() is not setting the conn_handle for the BLE_NUS_C_EVT_NUS_RX_EVT event, but you have access to the conn_handle in the p_ble_nus_c struct. Ideally it should also be set for the ble_nus_c_evt , i.e. ble_nus_c_evt.conn_handle = p_ble_nus_c->conn_handle; in on_hvx() . 
 When the nus_c service was initially designed, the nRF5 series only had support for one connection. Later the code was refactored and ble_nus_c_handles_assign() was added so we can keep track of what connection belongs to what instance of NUS. 
 So if the overall goal is to use the nus_c service in multiple connections, I recommend that you create a separate NUS and DB structure instance for each connection: 
 static ble_nus_c_t m_ble_nus_c[TOTAL_LINK_COUNT];
static uint8_t m_ble_nus_c_count; 
static ble_db_discovery_t m_ble_db_discovery[TOTAL_LINK_COUNT];
 
 Then each instance of NUS would have to be assigned a connection handle with ble_nus_c_handles_assign() when you get the event BLE_NUS_C_EVT_DISCOVERY_COMPLETE .
In nus_c_init() and db_discovery_init() you will need to initialize each instance. In nus_c_init() this could look something like this: 
 static void nus_c_init(void)
{
 uint32_t err_code;
 ble_nus_c_init_t nus_c_init_t;

 nus_c_init_t.evt_handler = ble_nus_c_evt_handler;
 
	for (m_ble_nus_c_count = 0; m_ble_nus_c_count < TOTAL_LINK_COUNT; m_ble_nus_c_count++)
 {
 err_code = ble_nus_c_init(&m_ble_nus_c[m_ble_nus_c_count], &nus_c_init_t);
 APP_ERROR_CHECK(err_code);
 }
 m_ble_nus_c_count = 0;
}
 
 The db_disc_handler() function would look something like this: 
 static void db_disc_handler(ble_db_discovery_evt_t * p_evt)
{
 ble_nus_c_on_db_disc_evt(&m_ble_nus_c[p_evt->conn_handle], p_evt);
}
 
 In ble_evt_dispatch() , ble_db_discovery_on_ble_evt() and ble_nus_c_on_ble_evt() should be changed to something like this: 
 uint16_t conn_handle;
conn_handle = p_ble_evt->evt.gap_evt.conn_handle;

ble_db_discovery_on_ble_evt(&m_ble_db_discovery[conn_handle], p_ble_evt);
ble_nus_c_on_ble_evt(&m_ble_nus_c[conn_handle],p_ble_evt);
 
 You should also take a look at the multilink central example in the SDK to see how this example handles multiple connections.

Mismatch between connection handles in ble_nus?

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