OpenThread devices fail to form network on BT840 modules

[Ry314]

Hello,

I have been working on a custom board that makes use of the Fanstel BT840XE and OpenThread. I have run into an issue where two boards refuse to join a network with one another. Curiously, if I include a nRF52840 DK in the network, the BT840s can send data to each other, presumably routing it through the nRF52840 DK. Both BT840s can ping and communicate with the nRF52840 DK, but will not ping each other in this scenario.

If the two BT840 boards are on their own and I try to commission an OpenThread following the steps in the On-Mesh Commissioning guide, I get "Join failed [NotFound]" after the "joiner start J01NME" step. Setting up the network parameters programmatically in the prj.conf files results with both devices making themselves leader, or one of them becoming detached, depending on the OpenThread feature set I use. 

Now, if I put the commissioner/client firmware on the nRF52840 DK and set it to use "nRF only," it works as expected.

I was wondering if there are hardware differences that are causing the problem, and I found this discussion: https://devzone.nordicsemi.com/f/nordic-q-a/58956/softdevice-not-working-on-bt840-based-custom-board/239383#239383
However, I am working with nRF Connect and Zephyr, and the only symbol I could find that seemed to be similar was CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y. Unfortunately, adding this line on both modules resulted in no change.

Does anyone have any ideas about what the issue could be? Are there other Kconfig settings that need to be adjusted when migrating to the BT840? Could it be an OpenThread problem? 

Thank you for any suggestions or advice!

[Bendik Heiskel]

Hi,

The BT840XE module have a Skyworks FEM in addition to the nRF52840, have you added support for front-end modules to you application?
Without the FEM configured correctly there is essentially no connection between the nRF52840 and the antenna, which could explain the behavior you are seeing.

Here is our documentation for adding support for a FEM, which includes whats needed for the SKY-66112 which is the FEM used in the BT840XE module:
https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/device_guides/working_with_fem.html#

 

Best regards,

Bendik

[Ry314]

Hi, Bendik, 

Thank you for your reply. After a couple weeks of frustrating troubleshoot, I have finally gotten the BT840XEs to communicate. You were right that the issue was due to the FEM, the SKY66112. But getting the FEM to work was a whole different matter. 
Eventually after some communication with Fanstel, I figured out that it was due to the SDK version I was using. v2.2.0 is not compatible, apparently, while v2.4.1 worked for me. 
I also had to completely reinstall my toolchain because I had compatibility issues trying to run two different toolchain versions. It needed a clean slate by that point. 

Cheers, 
Ryan