Unable to connect to bonded device on Android

[vtarantik]

Hi, I have a problem with BLE connection. When I bond to the device and then connect, everything works and connection is stable. When I kill the app and try to connect again to the bonded device, I get disconnected from the Android with status code 22(connection terminated by localhost).

Do you know the difference of these scenarios under the Android hood? I can't figure out why does this keep happening when the phone is obviously able to connect to the device after the bonding procedure.

For connection I use the standard code used in the Android examples, there is no magic going on.

Thanks a lot for your help.

[Aleksander Nowakowski]

What phone and Android version are you using? On older Android versions, around 4.3-4.4.x there were problems with bonding. The initial connection after device was bonded worked fine, but resuming secure connection after reconnection failed. I don't remember exactly on what phones this issue used to occur, but I'd say it was Nexus 4 or 7. I also don't know if there was something that could be done on the fw side as a workaround.

[vtarantik]

Thanks a lot for your reply. I've been trying it on Pixel with Android 8.0, Moto G4 with Android 7.0, Nexus 5 with Android 8.0 and also Nexus 6P with Android 8.0. The behavior is the same on all of those devices. I found out that if I try to connect to already paired device, the peripheral requests connection update with interval parameter set to 6, which is apparently not supported since Android 6 but I haven't found any documentation that says that if the device doesn't support the requested interval it can disconnect or request disconnection from the peripheral. Do you think that this could be the case?

[Aleksander Nowakowski]

Yes, that's is most likely the reason. In the connection parameters update you may specify the min and max conn interval, if you set both to 7.5ms both Android and iOS will disconnect. Android's minimum is 11.25, ios is 30ms. Could you try with this values?

[Aleksander Nowakowski]

For HID devices iOS has minimum 7.5ms, for others 30ms.

[Aleksander Nowakowski]

And one more thing: if possible, Android uses 7.5ms interval for the service discovery. When done it changes interval to a longer one.