DevAcademy Bluetooth LE connection problems

[Lars M]

Hi,

I am going through the DevAcademy Bluetooth LE lessons, using nRF5 DK. But I run into problems directly in the exercise of the first lesson. Everything goes fine to step 4.2, but connecting doesn’t work. Connection is established, but almost immediately disconnection happens. LED2 is lit for a short moment. The print outs are like this:

No matter how many times I try, disconnection always happens this way. I have also tested to connect via the Bluetooth low energy desktop app using the Nordic BLE dongle. Then the connection works fine. I have tested with both nRF Connect SDK 2.3.0 and 2.0.0, and the scenario is the same for both versions.

In the desktop app it is possible to read the button state and activate notifications (and receive updates when the button is pressed). But I am not able to control LED3. I have put a breakpoint in write_led() in lbs.c (C:\...\v2.3.0\nrf\subsys\bluetooth\services\lbs.c), but the breakpoint isn't hit when I write to the LED characteristic. Though, a breakpoint in read_button() will be hit when I click "Nordic LED and Button Service", so I should be in the correct file.

 

Best regards,

Lars

[Einarh]

Hello

What phone and OS are you using when the connection doesn't work? It could be the case that the connection parameters aren't compatible with your phone OS or something similar.

If you could set up a BLE sniffer and share logs of the communication between your devices as the disconnection happens, that would be very helpful.

Best regards,

Einar

[Lars M]

Hi,

I have a Samsung S21 5G with Android version 13. My computer runs Windows 10.

Now I have installed the BLE Sniffer and captured some communication. In this file I should have recorded two attempts to connect.

Best regards,
Lars

4214.Capture.pcapng

[Lars M]

That's the problem, I can't make it not work anymore. After the last part of lesson 3 exercise 2, connection always works. And that part has to do with some connection parameters (data length and time). Can something in this process have affected my phone to behave differently in coming connections?

It's a little while ago so I don't really remember, but most likely the file "Capture dk and phone, 3 tries.pcapng" is capture from lesson 1. As the two files I attached in previous post.

Can you say something about the red mark in packet 214? Why is it red when corresponding packet in another capture is not red? They look pretty much the same, apart from the red-marked comes after LL_CONNECTION_UPDATE_IND.

Another thing that I have encountered is that during these connection problems I have run the desktop program. Every time that I power on the dk that I used with the desktop program (I am playing with two dk:s) the PC automatically connects to it. I go into Windows settings and tell the computer to forget the device. Everything seems to work (the device disappears from the device list), but nonetheless the computer connects to it when it is turned on. I have manually added the dk, and then removed it, but it doesn't help. The computer connects to the dk no matter if it is in the list or not. The only way that I have found out to prevent my computer to connect to it is to turn off Bluetooth in the computer. Is there anything I can do to make the computer to really forget my dk?

/Lars

[Lars M]

Hi again,

The last part in previous post is solved. I had to restart my computer, and after that there is no automatic connection.

/Lars

[Einarh]

Lars M said:

After the last part of lesson 3 exercise 2, connection always works. And that part has to do with some connection parameters (data length and time).

Then it seems like this was the tweaking of parameters needed to make it work, and it also seems like your phone remembers these parameters. Hard to say exactly what made the difference without being able to reproduce the error though.

Lars M said:

Can you say something about the red mark in packet 214? Why is it red when corresponding packet in another capture is not red? They look pretty much the same, apart from the red-marked comes after LL_CONNECTION_UPDATE_IND.

The red mark seems to indicate an unexpected sequencing of packets yes, the peripheral sending a PHY_REQ when the central expects a reply to its CONNECTION_UPDATE_IND.

[Lars M]

Einarh said:

Then it seems like this was the tweaking of parameters needed to make it work, and it also seems like your phone remembers these parameters.

Ok, it's maybe like that. Though, it would be nice to know it for sure. But maybe it's hard to get to know that.

But if it is like this, these update of parameters used in lesson 3 exercise 2 should be present in all BLE-programs to prevent a phone to behave like mine.

/Lars

[Lars M]

Hi again,

Another thing that makes this not really satisfactory is that I had my phone working with my own-made BLE-project at the same time as the phone didn't work with the DevAcademy-projects. For my project, the phone didn't send LL_CONNECTION_UPDATE_IND as every other time when the connection works.

Lars M said:

I have made my own BLE-program (called MMS), which is a light version of NUS. Here the connection works fine. It is also possible to send characters to and receive notifications from my dk, and also disconnect. The only difference in the connection process seems to be the lack of LL_CONNECTION_UPDATE_IND in my project.

So maybe there is more to this than just the possibility that the parameter updates have made my phone behave in a new way. It obviously behaved differently depending on project before.

/Lars

[Lars M]

It feels this never comes to an end. Now I have run lesson 4 exercise 1, and now the connection problem is back. Lesson 3 exercise 2 works fine, and also MMS. But when I go back to lesson 4 exercise 1, the connection problem is still there, the phone hasn't changed behaviour (at least not to make this program work). I also tried lesson 1, and now that works.

I have captured a lot. I attach the files, numbered in the order they are logged. Though, actually there is nothing new. Every time conenction works, LL_CONNECTION_UPDATE_IND is missing. And every time connection doesn't work, LL_CONNECTION_UPDATE_IND is present.

/Lars

1 Capture dk first phone less4 exer1 not working, before less3 exer2.pcapng

2 Capture dk first phone MMS working, before less3 exer2.pcapng

3 Capture dk first phone less4 exer1 not working, before less3 exer2 after MMS.pcapng

4 Capture dk first phone less3 exer2 working.pcapng

5 Capture dk first phone less4 exer1 not working, after MMS after less3 exer2.pcapng

6 Capture dk first phone less1 exer1 working, after MMS after less3 exer2.pcapng

7 Capture dk first phone less4 exer1 not working, after MMS after less3 exer2 after less1.pcapng

[Einarh]

Hi, ignore the "suggested answer", I misclicked..

I've forwarded this internally at Nordic now, and someone is trying to reproduce this with a phone similar to yours.

I'll let you know if I get any updates.

-Einar

[Einarh]

Hello

I just received an update clarifying that this is a known issue with some Samsung phones related to the PHY update procedure.

It should work if you disable the PHY update from the peripheral side.

In order for this to work with the PHY update on your Samsung phone, this issue would have to be addressed by Samsung.

Best regards,

Einar

[Lars M]

By setting CONFIG_BT_PHY_UPDATE=n I get connection in the exercises working, great! At least those exercises in lesson 4. But now I can't use 2M, doesn't feel good.

After I set CONFIG_BT_PHY_UPDATE=n, I also tested to set back to CONFIG_BT_PHY_UPDATE=y. Then connection works. Strange. And 2M is used with 50 ms communication interval. The LL_CONNECTION_UPDATE_IND is missing this time.

Testing connection for another unaltered exercise from lesson 4 does not work, just as before. But setting CONFIG_BT_PHY_UPDATE=n makes it work. And connection works after setting it back to "y". Just as the scenario for previous exercise. This holds for all three exercises in lesson 4.

It feels like my phone recognizes the various projects. Can it be like that?

I have captured some logfiles, I attach four files from lesson 4 exercise 2. In the first file the exercise is unchanged, and connection doesn't work. The second file has CONFIG_BT_PHY_UPDATE=n. There is an LL_CONNECTION_UPDATE_IND with 7.5 ms as before, but then a lot of "new" communicaton goes on before the connection is established. Can you get some interesting information from this? Right before the connection is established there is a new LL_CONNECTION_UPDATE_IND with new parameters.

In the third file is CONFIG_BT_PHY_UPDATE set to "y" again. As mentioned above, now connection works. The fourth file has CONFIG_BT_PHY_UPDATE=n. Here all the "new" communication is missing.

Another thing that I don't understand is that CONFIG_BT_PERIPHERAL_PREF_MIN_INT says that the connection interval can be 7.5 ms, which my phone asks for when the connection doesn't work. Shouldn't LL_CONNECTION_UPDATE_IND with 7.5 ms work? Or is there something else that causes connection to not work?

Does any of Samsung or Nordic not follow the BLE standard?

Einarh said:

this is a known issue with some Samsung phones related to the PHY update procedure.

Do you know which/how many phones from Samsung that have this issue?

Is it only Samsung?

Best regards,
Lars

1 Capture Samsung S21 less4 exer2 CONFIG_BT_PHY_UPDATE=y.pcapng

2 Capture Samsung S21 less4 exer2 CONFIG_BT_PHY_UPDATE=n.pcapng

3 Capture Samsung S21 less4 exer2 CONFIG_BT_PHY_UPDATE=y.pcapng

4 Capture Samsung S21 less4 exer2 CONFIG_BT_PHY_UPDATE=n.pcapng

[Einarh]

Lars M said:

Does any of Samsung or Nordic not follow the BLE standard?

Yes exactly, the problem is that some Samsung phones don't follow the BLE standard.

So in your specific connection procedure, you end up in an undefined state and time out. Once you've established the first successful connection, your phone will remember the connection parameters, and the connection procedure will be different which means the error does not occur anymore.

I'm not sure exactly what phones are affected, only that it's a known issue with some Samsung phones right now. There have also been similar issues with iPhones previously. If it's important to you I could look into more specifically what phones are affected.

-Einar