Unable to connect to bonded device on Android

RE: Unable to connect to bonded device on Android

Aleksander Nowakowski — Thu, 09 Nov 2017 14:37:48 GMT

If you have a phone with Android 8+ in nRF Connect you'll see the connection parameter updates. Before service discovery there is an update with 7.5 ms, and after discovery some more updates with higher values (depending on the app). Looks like the security fails in your case, or service discovery. It sets interval to 7.5ms, starts discovery/resuming security and fails, and disconnects.

RE: Unable to connect to bonded device on Android

vtarantik — Thu, 09 Nov 2017 14:32:25 GMT

Oh, I see, but it's still weird since when I connect right after the bonding, I can sometimes see a couple of connection updates with interval value set to 36 and it works. When I kill the app, or disconnect from the peripheral and try to connect again, I can only see one connection update with interval value set to 6 followed by disconnect. Could you please point me to the place where you found this info about the 7.5ms interval for discovery? Maybe I can find some more there. And thank you once again for helping me here, I'm starting to be desperate.

RE: Unable to connect to bonded device on Android

Aleksander Nowakowski — Thu, 09 Nov 2017 10:05:40 GMT

It does come from the Android system. After successful bonding Android repeats service discovery. To make it faster they change connection interval to 7.5ms, but just for the discover. When it's done a new connection param update will come with higher value.

RE: Unable to connect to bonded device on Android

vtarantik — Thu, 09 Nov 2017 10:01:05 GMT

Well, we've tried to change the FW on peripheral side but no success, no matter which parameter value we put in the peripheral, I'm still getting connection update with interval 6. I started to wonder whether this couldn't be coming from the phone but it shouldn't make sense since this value isn't supported by the system. Do you think that it's possible that it's coming from the phone?

RE: Unable to connect to bonded device on Android

vtarantik — Sat, 04 Nov 2017 16:42:01 GMT

Well, I'll be able to try day after tomorrow so I'll let you know. The weird thing is that iOS never disconnects from the peripheral, only Android so I'm not sure if this can be the case. I'm thinking whether iOS doesn't have some better handling of this case since it stays connected. Thanks again for your tips..

RE: Unable to connect to bonded device on Android

Aleksander Nowakowski — Sat, 04 Nov 2017 06:09:29 GMT

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

RE: Unable to connect to bonded device on Android

Aleksander Nowakowski — Sat, 04 Nov 2017 05:58:17 GMT

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

RE: Unable to connect to bonded device on Android

Aleksander Nowakowski — Sat, 04 Nov 2017 05:57:19 GMT

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?

RE: Unable to connect to bonded device on Android

vtarantik — Sat, 04 Nov 2017 05:47:14 GMT

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?

RE: Unable to connect to bonded device on Android

Aleksander Nowakowski — Fri, 03 Nov 2017 15:45:51 GMT

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.