Softdevice Controller does not send HCI event "LE Data Length Change"

[Adrian Eggenberger]

I've built a firmware based on the hci_uart sample with the softdevice controller. The board is custom made and has a nrf52840 on it. Over USB-CDC HCI commands are sent to the device.

Most things seem to work fine, but I've found out, that the softdevice controller does not send the "LE Data Length Change" event. 

Test-Case:
- Send HCI commands to initialize the contoller
- Scan for devices
- Connect a device
- Initiate a data length update

Expected:
- The controller should send a data length changed event over HCI.

Actual:
- No event is generated

I've recorded the HCI communication for verification. In wireshark I see that no data length changed is generated. The HCI log is attached.capture.zip

I've checked, that the event mask is configured correctly. Also has the remote device support for data length extension. The same test with a PTS dongle works as expected. What can be wrong here?

Environment:
- nRF Connect SDK/Toolchain 2.9.0

[Adrian Eggenberger]

I've made some more observations. If the DLE event is not triggered the data length is not increased at all. It seems as the request is ignored.

Another thing that came up is that the configuration has an impact. In the setup where DLE is not working all ISO features are enabled (this is required). When I comment out all ISO features from the configuration file it works as expected.

I've added the working and the not working configuration here:

dle-works.confdle-not-working.conf

[Hung Bui]

Hi Adrian, 
I assume the issue is now resolved and you don't have further question ? 
I am not sure if this is needed in your case but if you want the application to control the data length update you would need to enable CONFIG_BT_USER_DATA_LEN_UPDATE=y on the host's side.

[Adrian Eggenberger]

Hi Hung

No. it‘s not resolved. As we need all ISO Features we would need a softdevice that behaves properly. 
Thanks for the hint on the host side. In this project we don’t need nRF Connect as host.

Regards Adrian

[Hung Bui]

Hi Adrian, 

Do you get any return from the controller when you try to trigger DLE (with ISO features enabled) ? 

We will try to reproduce the issue here to see if we have the same problem. If you can provide a sample that we can try it would be much appreciated. 

[Adrian Eggenberger]

Hi Hung

The controller does respond to the DLE command with a „Command complete“ as expected.
I‘ll create a simple sample for reproduction. I get back to you in a few days when it‘s ready.

Regards Adrian