Data Length Update on nRF7002-DK

[Ted Jones]

I am using the nRF7002-DK to implement a BLE interface.  I need to send packets > 23 bytes through a notification characteristic.  I am currently using nRF Connect on an android device to connect to it

In my prj.conf file I have the following:

CONFIG_BT_BUF_CMD_TX_SIZE=255

CONFIG_BT_BUF_EVT_RX_SIZE=255

CONFIG_BT_BUF_ACL_TX_SIZE=251

CONFIG_BT_BUF_ACL_RX_SIZE=251

CONFIG_BT_L2CAP_TX_MTU=247

I am calling bt_conn_le_data_len_update with 247 as the tx_max_len and 3750 as tx_max_time.  I have a data length update callback which is called after this but the data len info struct always has tx_max_len set to 27 and tx_max_time set to 2120.  I don't care much about the time but I don't understand why I can't get the tx_max_len set to more than 27.

One thought that I had is that I am only flashing the app cpu.  Do I need to re-flash the net cpu in order to change the max MTU?  If so, is there a sample application for it?  The documentation isn't clear on this.

Thanks!

[Vidar Berg]

Hello,

The radio packet length should be set to the maximum, which is 251 bytes. This allows the entire 247 byte ATT packet to fit into a single on-air packet. Support for the max. radio packet length (default:27) must be enabled in the ipc_radio FW running on the network core like how it's done in our BLE throughput sample here:  https://github.com/nrfconnect/sdk-nrf/blob/main/samples/bluetooth/throughput/sysbuild/ipc_radio/prj.conf#L21-L23. CONFIG_BT_AUTO_DATA_LEN_UPDATE is also enabled by default, which means you to not have to initiate the update yourself.

Best regards,

Vidar

[Ted Jones]

Thanks Vidar.  I appreciate your quick response but I am still a little confused.  In the case of the throughput example is the entire code base being built for the network core?  I am building my application for the application core, I am not sure what needs to be built/flashed to the network core.  I will need to support both BLE and WiFi.

Thanks.

[Vidar Berg]

The RADIO peripheral is only available to the network core, so any application that relies on the RADIO must have firmware running on the network core. In the case of Bluetooth, the bluetooth host typically runs on the application core, while the bluetooth controller resides on the network core (https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/app_dev/device_guides/nrf53/features_nrf53.html#bluetooth_low_energy)

The throughput sample is for for the application core, but uses sysbuild (see https://academy.nordicsemi.com/courses/nrf-connect-sdk-intermediate/lessons/lesson-8-sysbuild/) to also include ipc_radio in the build. Both the app and network core will be programmed when you click "flash".

If you’re using our VS Code extension to build your project, you can see which projects are included in the build from the APPLICATIONS view.