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

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

Adrian Eggenberger — Thu, 09 Jan 2025 13:03:53 GMT

Hi Hung

Thanks for the feedback. With that info I think I can set the best configuration for my project.
Issue can be closed here.

Regards Adrian

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

Hung Bui — Thu, 09 Jan 2025 11:43:43 GMT

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.

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

Adrian Eggenberger — Wed, 08 Jan 2025 16:25:26 GMT

Hi Hung
I can reproduce your findings. If I add the configuration you mention it works as expected. Anyhow it would be great to know why the limitation was set in first place to know if the override has some downsides. Looking forward to hear the input from your team.
Regards Adrian

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

Hung Bui — Wed, 08 Jan 2025 13:30:29 GMT

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 .

devzone.nordicsemi.com/.../4073.hci_5F00_uart.zip

devzone.nordicsemi.com/.../5140.peripheral_5F00_uart_5F00_hci.zip

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

Adrian Eggenberger — Sat, 04 Jan 2025 08:57:35 GMT

Hi Hung

I've created a sample to reproduce the issue. It is basically the hci_lpuart example with configuration for the softdevice controller. The project is attached with built files for a nrf52840DK. There are two builds included. One build without ISO features and one with the ISO features. The HCI is configured to the VCOM of the nRF52840DK and uses 115200Baud.

devzone.nordicsemi.com/.../hci_5F00_lpuart.zip

To build the example the following command lines have been used with NCS 2.9.0:

DLE WORKS (without ISO support)
west build -b nrf52840dk/nrf52840 --pristine --build-dir "build_nrf52840dk_dle-works_cli" -- -DCONF_FILE=prj.conf -DEXTRA_CONF_FILE="dle-works.conf" -DCMAKE_BUILD_TYPE=Release -DBOARD_ROOT="."

DLE DOESN'T WORK (with ISO support)
west build -b nrf52840dk/nrf52840 --pristine --build-dir "build_nrf52840dk_dle-not-working_cli" -- -DCONF_FILE=prj.conf -DEXTRA_CONF_FILE="dle-not-working.conf" -DCMAKE_BUILD_TYPE=Release -DBOARD_ROOT="."

Hope that helps to reproduce the issue.

Regards Adrian

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

Adrian Eggenberger — Thu, 02 Jan 2025 17:29:39 GMT

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

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

Hung Bui — Thu, 02 Jan 2025 16:33:33 GMT

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.

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

Adrian Eggenberger — Mon, 30 Dec 2024 22:36:32 GMT

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

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

Hung Bui — Mon, 30 Dec 2024 14:30:49 GMT

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.

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

Adrian Eggenberger — Sat, 28 Dec 2024 10:25:20 GMT

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:

devzone.nordicsemi.com/.../dle_2D00_works.conf devzone.nordicsemi.com/.../dle_2D00_not_2D00_working.conf