nRF5340 - Reconnecting after bonding disconnect with reason 0x3d

[Gabriele]

Hello,

Ubuntu
NCS 1.9.2

My nRF5340-based Peripheral can pair and bond with Windows PC, running nRF Connect For Desktop Bluetooth LE Standalone v4.0.0 (linked to nRF52840-DK).
After successful bonding, with the "LE Secure Connection pairing" option enabled on Central, subsequent connections fail.

At Central side (PC) I see disconnection reason is BLE_HCI_CONNECTION_TIMEOUT

At Peripheral side (nRF5340) I get disconnection reason 0x3d

Who and why made this disconnection ?
Hint: if I uncheck the LE SC option, everything works fine.

[ovrebekk]

Hi

I tried the same thing myself, and I seem to be able to reproduce the problem. 

I will need to spend a bit more time to investigate this, and I will get back to you with an update tomorrow. 

Best regards
Torbjørn

[Gabriele]

Thank you Torbjørn

[ovrebekk]

Hi 

Sorry for the slow response. 

The issue seems to be related to some of the flags shared during the pairing process. 

A colleague helped me out with this and found that when running a nRF5 SDK Bluetooth example with LESC enabled the issue did not occur. 

One difference between these two versions is that there are some additional flags that are set when bonding with the nRF5 SDK example (on the right) that were not set in the NCS example:

The leading theory right now is that the issue is on the nRF Connect for Desktop side, since these flags should not need to be set for the pairing and bonding to work. 

I will have to follow this up with the tools team and get back to you later.  

Best regards
Torbjørn

[Gabriele]

Ok Torbjørn,

thank you for this finding. Therefore I assume I do not need to fix anything on the target side. Let me know the feedback from the tools team 

[Hung Bui]

Hi Gabriele, 

Just an update regarding this issue. The team has verified that there is a bug in the library to handle key retrieval. It will take some time to have a fix on this. For now it's consider a known issue and don't have a workaround yet, unfortunately.