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, 
I did a quick test here and got a result that when I enable ISO related configuration, the maximum data length is set to 27. 

I still can request the data length request and can see that with the sniffer but it's limited to 27 bytes. This could be the reason you don't see that in your test because the length is already 27 (?).

When i enabled the following configuration: 

CONFIG_BT_CTLR_SDC_MAX_CONN_EVENT_LEN_DEFAULT_OVERRIDE=y

CONFIG_BT_CTLR_SDC_MAX_CONN_EVENT_LEN_DEFAULT=5000

I was able to request the data length as I want: 


You can see some dependency here between BT_ISO and event length (which affect data length) 
https://github.com/nrfconnect/sdk-nrf/blob/main/subsys/bluetooth/controller/Kconfig#L156C8-L156C46

I will check with the team internally to see why BT_ISO would cause that effect. I believe it must be something in the spec mandate this. 

I attached here the code I tested (I used hci_uart instead of hci_lpuart but that shouldn't change the behavior). 

The host is peripheral_uart . 

4073.hci_uart.zip

5140.peripheral_uart_hci.zip