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

[Hung Bui]

Hi Adrian, 
The info I got from the team is that when BT_ISO is enabled we automatically assume that ACL (normal BLE communication) shouldn't have the highest priority hence we give it the minimum event time to give more air time for BT_ISO. 
If you want to have longer data length with ACL, the configurations I showed should be used.