Android phone loses bonding information when trying to read characteristic

[Acutetech]

I have an issue with bonding between a PCA10040 running the sample Glucose app and an Acer tablet running Android 7 and nRF Toolbox. I have not seen the problem on a second (Asus) tablet or a Samsung phone (Android 8). I can set up a bond and interact with the peripheral, but when I try to connect a second time, the peripheral disconnects immediately and then the tablet loses its bonding after about 19s.

Here is a typical sequence (although other variants also occur):

1   Ensure the peripheral is removed from the Paired Devices list on the tablet.

2   Remove pairing from the peripheral by holding down Button 2 during power on.

3   Run the nRF Toolbox Glucose monitor app and connect to the peripheral. The peripheral prints a passkey which I enter. Toast says the device is now bonded and I see it appears in the Paired Devices list on the tablet.

4   I use nRF Toolbox to disconnect from the peripheral, then attempt to connect again. The peripheral appears in the list of "Bonded devices".

5   The peripheral reports "Glucose example started, Fast advertising, Connected, Connection secured: role: Peripheral, conn_handle: 0, procedure: Encryption,  Link secured. Role: 1. conn_handle: 0, Procedure: 0, Fast advertising, Disconnected".  The disconnect is immediate.

6   The app does not immediately notice that the peripheral has disconnected. After a while the "Disconnect" button changes to "Connect"

7   When I click on "Connect" the peripheral now appears in the "Available devices" section in the "Select device:" dialog, rather than the "Paired Devices" section. Furthermore, if I go to Settings>Bluetooth, it also appears in the "Available devices" section. In other words, the tablet has forgotten the pairing. The peripheral presumably thinks it is still paired.

8   If I try to connect in nRF Toolbox, the app makes a sound, Toast says "bonding with the device", the peripheral prints "Connected", then after a delay, Toast says "bonding failed" and the peripheral prints: "BLE_GAP_EVT_AUTH_STATUS: status=0x1 bond=0x0 lv4: 0 kdist_own:0x0 kdist_peer:0x0, Fast advertising, Disconnected".

At this stage the only way to recover is to remove the pairing from the peripheral.

When I look at the nRF logs, in the failure case errors start when nRF Toolbox tries to read the battery characteristic. Typically I see error (0x85). In some log files (but not all) I see "[Broadcast] Action received: android.bluettoth.device.action.BOND_STATE_CHANGED, bond state changed to: BOND_NONE (10)"

I see the problems when I use nRF Toolkit downloaded from Playstore and built from the Github Master branch.

Sometimes the app makes a sound, Toast says "Bonding with the device" but the dialog asking for the passkey does not appear, and the peripheral does not print a passkey.

I can predict when the loss of pairing is about to happen. I go to the Settings Bluetooth screen and see the peripheral in the list of bonded devices. After a few sections I see Toast "Error on reading characteristic 133" error, and at the same moment the peripheral moves from the "Bonded devices" list to the "Available devices" list. In the case, nRF Logger shows the app is trying to read teh battery characteristic, then about 19s later the BOND_STATE_CHANGE message is printed, then the Error (0x85). Note in this case that while the tablet thinks it is connected, the peripheral has disconnected almost immediately after it connected.

[Sigurd]

Hi,

I have not seen this issue before.

What SDK version did you test this with? 

If you have another nRF52-DK, it could be interesting to see the results of a sniffer log. See this and this page.

[Acutetech]

Hi Sigurd. As I wrote above, on the second connection nRF Connect thinks it is connected, but the peripheral connects and disconnects very quickly. After 19s the nRF Logger prints that the bonding has changed to BOND_NONE, then shows a 0x85 GATT Error.

I added code to print the disconnect reason and I see this:

<info> app: Connected
<info> peer_manager_handler: Connection secured: role: Peripheral, conn_handle: 0, procedure: Encryption
<info> app: Link secured. Role: 1. conn_handle: 0, Procedure: 0
<info> app: Fast advertising
<info> app: Disconnected, reason 61.

Error 61 (0x3D) is described in these posts:

https://devzone.nordicsemi.com/f/nordic-q-a/25583/error-0x3d-disconnected-reason-61-sdk12-3

https://devzone.nordicsemi.com/f/nordic-q-a/26287/connections-to-moto-e4-fail-with-0x3d-connection-terminated-due-to-mic-failure

The second post suggests a fix but I don't understand it. main.c contains this line - should I change it, and what to:

    cp_init.start_on_notify_cccd_handle    = BLE_GATT_HANDLE_INVALID;

There are two questions in my mind:

1  Why is the peripheral disconnecting with reason 61, and how do I avoid this?

2  Why is the tablet losing the bonding information, and how to avoid it? Is the bonding being lost because of explicit action by nRF Toolkit or the Android BLE Library, or is this being done by the BLE stack in my phone as a result of the earlier error?

FYI, I can operate the same tablet plus nRF Toolkit with a Glucose peripheral based on a CSR development board without this problem.

[Sigurd]

Acutetech said:

1  Why is the peripheral disconnecting with reason 61, and how do I avoid this?

Generally, you will get this error if you use incorrect encryption keys when you try to encrypt the link with a bonded device. As mentioned before, a sniffer log could help us identify the problem.

What SDK version is this? If you are using an old SDK version, please try to use latest version(SDK 15.2).

Acutetech said:

2  Why is the tablet losing the bonding information, and how to avoid it? Is the bonding being lost because of explicit action by nRF Toolkit or the Android BLE Library, or is this being done by the BLE stack in my phone as a result of the earlier error?

I believe that this is caused by issues in the native BLE stack on the phone. Maybe triggered by some BLE procedure it’s not handling correctly. Do you see the same issue if you use nRFConnect instead ? See this link. 

[Acutetech]

I get the same results when I use nRF Connect. The first connection gives a bond and I can access the peripheral, but the second connection gives the 61 error and the bonding is lost from the tablet.

I have programmed the PCA10040 with the "latest" code (SDK downloaded 31/10/18 with this path:)
C:\Users\charl\Development\nRF5_SDK_15.2.0_9412b96\examples\ble_peripheral\ble_app_gls I believe this uses the s132 SoftDevice.

I downloaded the sniffer package but it does not look like I have hardware that will permit me to run this at the moment.
I have PCA10059 dongles but it looks like the sniffer does not work with these. Can this be done? Or could I run the Glucose app on the dongle? Otherwise looks like I have to find some extra hardware.

[Acutetech]

I get the same result if I use LightBlue Explorer instead of nRF Connect.

Can you comment on the fix reported in one of the links above? I don't know how I can do that.

AFAIK, neither nRF Logger nor the glucose app reports on either conn param negotiation or encryption events. Can these be turned on and examined?