Unexpected disconnection (reason 22)

Question

Platform: NRF52832, s132_nrf52_6.0.0, SDK 15.0 Remote: iPad (12.1.4) with proprietary APP Use-Case: APP (Central) connects to Platform and reads continuesly data via RX-TX-characteristics (~1 kBytes\s) Problem: Always after ~4 hours the Platform terminates the connection "gap_evt.params.disconnected.reason = 22" 
 From the Air-Trace I can see following at the end (unsure if the trace is reliable): --- MASTER LLCP Channel Map Indication (Used: 0-9,11-14,16,19,21-36 / Unused: 10,15,17-18,20, Inst=25'235 (+399) | 14.532.478 154 625 (+11.970 s)) MASTER LLCP Channel Map Indication (Used: 0-9,11-14,16,19,21-32,34-36 / Unused: 10,15,17-18,20,33, Inst=25'502 (+398) | 14.540.488 335 375 (+11.940 s)) MASTER LLCP Channel Map Indication (Used: 0-9,11-14,16-19,22-32,34-36 / Unused: 10,15,20-21,33, Inst=25'769 (+398) | 14.548.498 514 250 (+11.940 s)) SLAVE LLCP Reject Extended Indication (Connection Update Indication, Page Timeout) SLAVE LLCP Ping SLAVE LLCP Termination (Unacceptable Connection Parameters) --- 
 Best Regards Stefanos

Stefanos · Answer

I found the problem (I called by mistake "sd_ble_gap_disconnect"): I have set the defines "FIRST_CONN_PARAMS_UPDATE_DELAY" and "NEXT_CONN_PARAMS_UPDATE_DELAY" to a too high value so that the disconnection happend exaclty afte 4 hours. The config "cp_init.disconnect_on_fail = false" was set correctly but I had still following example code: --- static void on_conn_params_evt(ble_conn_params_evt_t * p_evt) { if (p_evt->evt_type == BLE_CONN_PARAMS_EVT_FAILED) { ... err_code = sd_ble_gap_disconnect(m_conn_handle, BLE_HCI_CONN_INTERVAL_UNACCEPTABLE); } } --- We are using a self-made iOS-Test-APP. The APP is reading some process values from the product (i.e. speed, pressure, power, temperature ...) and additionally you can configure the product. To communicate with the product we have a proprietary protocol which we just exchange via a RX-TX-ATT-Characteristics. 
 In normal mode we need between 0.5 - 1 kBytes\sec to retrieve all information in a proper time. But for SW-Download we need to transfer a lot of file where we would like to use the smalles connection-interval. Currently (with our previous BT solution) we reach with the iPAD only 3.5 kBytes\sec instead of possible ~15 kBytes). 
 I tried to set following connection-interval: #define MIN_CONN_INTERVAL MSEC_TO_UNITS(20, UNIT_1_25_MS) #define MAX_CONN_INTERVAL MSEC_TO_UNITS(75, UNIT_1_25_MS) 
 But from the air-trace I see following: after 5 sec. the platform sends a L2CAP_Parameter_Update(Conn. Interval Min = 0xFFFF \ Conn. Interval Max = 0xFFFF) after 35 sec. the platform sends a L2CAP_Parameter_Update(Conn. Interval Min = 0xFFFF \ Conn. Interval Max = 0xFFFF) after 65 sec. the platform sends a L2CAP_Parameter_Update(Conn. Interval Min = 0xFFFF \ Conn. Interval Max = 0xFFFF) after 95 sec. I called by mistake the "sd_ble_gap_disconnect" 
 Can you help with following questions: - Why we see in the air-trace the Connection-Interval set to 0xFFFF instead of 0x000F ? - Why you provide the feature "FIRST_CONN_PARAMS_UPDATE_DELAY" ? I am asking because I possible have some IOP issues in our previous BT-solution where we send the update-request immediatelly. - Do you have some recommendation how to set the connection-interval to reach the highest datathroughput ? In out previous BT-solution i tried (1st-try: min7.5ms\max7.5ms) (2nd-try min7.5\max=10.5) ... THANKS Best Regards Stefanos