BLE keep connection alive

[roman_tl]

What is the proper way of keeping connection from Client to Server alive?

I'm working with smart glasses and after connection STM32 client sends the data, however, after some 10-20 seconds or so glasses show "Client disconnected" message.

What puzzles me is that I constantly send new messages every 2 seconds, so connection should be alive, but it's not.

The other strange thing is when I connect to laptop's Bluetooth, inside LightBlue logs I constantly see fresh messages every 2 seconds continuously as expected, for as long as client device is powered on.

Is there any check to periodically refresh connection state, or what's the right way?

Update: do I need to handle Server's notification in any way to keep connection alive?

[roman_tl]

I found one part of the problem - in this method

    result = aci_gap_create_connection(SCAN_P,
                                       SCAN_L,
                                       GAP_PUBLIC_ADDR,
                                       P2P_SERVER1_BDADDR,
                                       GAP_PUBLIC_ADDR,
                                       CONN_P1,
                                       CONN_P2,
                                       0,
                                       SUPERV_TIMEOUT,
                                       CONN_L1,
                                       CONN_L2);

I got much faster connects and response by setting

Connection Interval: 15ms - 30ms
Slave Latency: 0
Supervision Timeout: 4s

The values were taken from "Peripheral Preferred Connection Parameters" characteristic of Server device. You can find them either in documentation or from device itself by reading

Generic Access service - UUID 0x1800

Characteristics:

Peripheral Preferred Connection Parameters

00002A04-0000-1000-8000-00805F9B34FB

The client still disconnects, and after timing this with stopwatch I see that Disconnect is happening around every 32 seconds - suspiciously close to maximum possible value of Supervision Timeout

Any ideas why that might happen? I'm pretty sure I'm passing 4s to aci_gap_create_connection and I see the same in p_connection_complete_event->Supervision_Timeout inside HCI_LE_CONNECTION_COMPLETE_SUBEVT_CODE

[STTwo-32]

Hello @roman_tl 

Have you updated your FUS and wireless stack to the last version (available on the V1.20.0 of the SDK).

Best Regards.

STTwo-32