Problems while discovering services on a multilink central

Question

Hi, 
 
 I developped a multilink central based on the example code ble_app_multilink_central. 
 I want to connect to several peripherals with two different custom services as shown in the following schematic.

The connection work but I have problems while discovering the services. 
 Sometimes the central discover all the services but often some services are not discovered and I don't understand why. 
 The discovery handler executes many times for each connection and the event type is often BLE_DB_DISCOVERY_ERROR. 
 Here is my discovery handler : 
 
 Here is an example of what can happen during a connection with 2 RFID and 1 Relay : 
 
 Here we can see that we have the relay on conn_handle 0x0 and the RFIDs on conn_handle 0x1 and 0x2. 
 We can see that the RFID service is not discovered on the conn_handle 0x1. 
 
 My questions are : 
 -When does the discovery handler execute for each connection? 
 -How to obtain the event BLE_DB_DISCOVERY_COMPLETE? 
 -Why does the discovery handler execute several time on each connection? And why is it not executed again while the service is not discovered?

Hung Bui · Accepted Answer

Hi Jules, 
 I think I found something wrong here. 
 As you can see in the log, the p_relay_c->uuid_type showing quite strange value (21, 178). 
 I think it was because of this function: 
 static void db_disc_handler(ble_db_discovery_evt_t * p_evt) { rfid_on_db_disc_evt(&m_rfid_c[p_evt->conn_handle], p_evt); relay_on_db_disc_evt(&m_relay_c[p_evt->conn_handle], p_evt); } 
 
 In our multilink example this work because we only have one service lbs and there can be a simple match between the index of the m_lbs_c array and the index of connection handle. When it's not the case with your application. 
 You are declaring m_rfid_c array with the size of 7 and m_relay_c with size of 1 . Calling a function using m_relay_c[p_evt->conn_handle] will cause trouble if the conn_handle is not equal to 0. 
 And since you don't know which one will be the first one to connect you can't be sure that the conn_handle = 0 will be always be the relay. 
 So you need to define a table that keep track of the connection handle that match with the relay and the list of active RFID node in an array. And keep that table (array) up to date on each CONNECTED/DISCONNECTED event. (You can detect if a device is a relay or a RFID by the if check inside rfid_on_db_disc_evt() and relay_on_db_disc_evt() )

Problems while discovering services on a multilink central

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