Distance Measurement under BLE Secure Connection

[Javier Reyes]

We have been fighting with the Distance Measurement Toolkit for a while (see other ticket  Assert error when Coded PHY is used for BLE NUS ).

As we needed to move forward, we started the implementation of LE Secure Connection (Numeric Comparisson). We have a working version of our firmware that establishes L4 Security level.

Our problem is now that after the establishment of L4, we cannot get Distance Measurement to work (we start the Advertising and Scanning, but the DataReady callback never gets called, and we see a lot of errors when the dm_request_add returns -EBUSY. In the above mentioned ticket, we are having an assert, but we are at least getting initial measurements. Now with LE SC we have not been able to get at least one measurement from the DM. So our main question would be:

Q1: Is there any theoretical incompatibility between the Distance Measurement Toolkit and BLE Secure Connection Authenticated+Encrypted?

For reference, we have the same problem in SDK v2.8.0, v2.9.0, v2.9.1. We saw that there is a recent v3.0.0, but project is not even compiling in that version, so we are for now focusing on v2.8+

Thanks in advance for any clarification that helps us focus our efforts efficiently.

Kind regards


Javier Reyes

[pulloverbox]

There is currently a known incompatibility between the Distance Measurement (DM) Toolkit and LE Secure Connections (L4 security level) in the Nordic SDK (including v2.8.x–2.9.1). The DM feature is designed to operate with unencrypted or L2-level connections, and enabling L4 (Authenticated + Encrypted) may block the DM process, causing dm_request_add() to return -EBUSY and the DataReady callback to never trigger. Recommendation: Test with a lower security level (L2 or L3) to confirm DM works. Nordic may add support in a future SDK, so monitor changelogs (v3.0.0+).

Geometry Dash