missing BLE_GAP_EVT_DISCONNECTED event

[popengut]

Our product acts as peripheral managed by application running on android. Usually when application is closed the BLE_GAP_EVT_DISCONNECTED event is delivered to device and so it can enter advertising mode again. However it appears that in some (very rare) cases the android app is being closed and no BLE_GAP_EVT_DISCONNECTED arrives. I would blame android/application for keeping the connection alive, but no BLE_GAP_EVT_DISCONNECTED arrives even when the phone is rebooted. From my understanding BLE stack should terminate connection after connection supervision timeout is expired (set to 5 sec in my case), and usually this is what happens, but not in 100% of cases..

What can possibly cause to SD to not deliver BLE_GAP_EVT_DISCONNECTED event?

The device code was developed some time ago and it is based on SDK 16 and SD 6.1.1

Please advice

[Edvin]

Hello,
I am sorry, but we are short staffed this week due to Public Holidays in Norway. We will be back on Monday 22nd and hope to be able to answer all incoming requests within a couple of days, depending on the backlog. I am sorry for the inconvenience.

Best regards,
Edvin

[Einar Thorsrud]

Hi,

Some events can be dropped, but the BLE_GAP_EVT_DISCONNECTED events have higher priorities are are never purposely dropped. There is a known issue where the application might not receive a BLE_GAP_EVT_DISCONNECTED event if the application does not continuously pull events from the SoftDevice. This bug exist in SoftDevice 6.1.1 which you are using, and is fixed in 7.3.0. If this is the issue you are seeing you can fix it by migrating to that SoftDevice, or by making sure that the application SoftDevice events faster.

[popengut]

Thanks, Einar
I also noticed that old SDK code from nrf_sdh_freertos.c was used, where SD task and ISR was synchronized by means of vTaskSuspend() and xTaskResumeFromISR() and not by task notifications, which can cause to ISR to be missed