Data forwarder

This sample streams real sensor measurements from a development kit to a host computer. It uses a CBOR-based framing protocol for Data Forwarder Host tool, with an optional ASCII mode for Edge Impulse’s data forwarder CLI compatibility.

Requirements

The sample supports the following development kits:

Hardware platforms

PCA

Board name

Board target

nRF54L15TAG

PCA20072

nrf54l15tag

nrf54l15tag/nrf54l15/cpuapp

When using Bluetooth LE transport, your host must be able to connect to the peripheral directly. If it cannot connect, you need a second development kit running the Nordic central UART sample as a USB serial bridge.

The default configuration on the nRF54L15 TAG reads a 6-axis BMI270 IMU and appends environmental data from an on-board BME688 sensor.

Overview

The sample periodically reads data from an on-board sensor and forwards it to a host over Nordic UART Service (NUS) (default) or UART. By default, the sample uses CBOR messages wrapped in COBS framing, as defined in cddl/data_forwarder.cddl. Session metadata is sent periodically so a host can join an active stream.

The sample performs the following operations:

  • Initializes the selected sensor driver and starts sampling at a fixed rate.

  • Encodes each sample and sends it through the configured transport.

Transport

The sample can send protocol frames to the host over Bluetooth LE or UART. Select the transport using the DATA_FWD_TRANSPORT Kconfig option.

Bluetooth LE NUS

Sample uses Nordic UART Service (NUS) for sending the protocol frames.

UART transport

Sample uses UART for sending the protocol frames.

Note

UART transport is not available on the nRF54L15 TAG device without any external UART-to-USB converter.

Increasing throughput

If you need higher streaming bandwidth, apply the following adjustments:

Bluetooth LE with direct host connection

When using Data Forwarder Host tool over Bluetooth LE on the host:

  1. Disconnect or move other Bluetooth devices off the same adapter. A single controller shares radio airtime across all active links, which reduces stream bandwidth.

  2. Follow the Bluetooth LE throughput tuning procedure in tools/data_forwarder_host/docs/ble_throughput_tuning.md.

Bluetooth LE with Central UART on a second DK

On the development kit running the Nordic central UART sample sample, set the following options in prj.conf to increase the NUS notification payload size:

CONFIG_BT_L2CAP_TX_MTU=247
CONFIG_BT_BUF_ACL_RX_SIZE=251

The Data forwarder sample sets matching MTU values on the peripheral side. You may also increase the Central UART baud rate in its board overlay (for example, current-speed = <921600>; on the relay UART node).

UART

Increase the baud rate of the data UART by setting the current-speed property in the board overlay. For example, to use 921600 baud:

&uart20 {
   current-speed = <921600>;
};

Protocol

The sample encodes sensor readings into protocol frames before sending them to the host. Zephyr sensor drivers return values stored in struct sensor_value. These are typically physical values converted by driver from raw sensor readings.

Data forwarder protocol supports float and integer sample formats. Sensor wrappers provided by the sample return physical value as a float, or as an integer in micro units, depending on the CONFIG_DATA_FWD_PROTO_INT32_VALUES Kconfig option.

Configuration

See Configuring and building for information about how to permanently or temporarily change the configuration.

The following sample-specific Kconfig options are used in this sample:

CONFIG_DATA_FWD_PROTO

(bool) Data Forwarder protocol

CONFIG_DATA_FWD_PROTO_RING_BUF_SIZE

(int) Ring buffer size in bytes

Size of protocol producer queue in bytes.

CONFIG_DATA_FWD_PROTO_ASCII_MODE

(bool) ASCII output mode

Replaces CBOR binary framing with CSV output limited to just sensor values.

CONFIG_DATA_FWD_PROTO_CRC

(bool) Append CRC-16 to every frame

Enabled for integrity checking on host side.

CONFIG_DATA_FWD_PROTO_META_RESEND_S

(int) Session info resend period (s)

Periodic resend of session-info for late joining hosts.

CONFIG_DATA_FWD_PROTO_MAX_CHANNELS

(int) Max number of sensor channels

Derived maximum count for zcbor generated arrays.

CONFIG_DATA_FWD_PROTO_INT32_VALUES

(bool) 32-bit integers for channel values

Use 32-bit integers instead of floats in the protocol.

CONFIG_DATA_FWD_TRANSPORT_BLE_NUS

(bool) BLE NUS

CONFIG_DATA_FWD_TRANSPORT_UART

(bool) UART

CONFIG_DATA_FWD_SENSOR_BMI270

(bool) BMI270 (6-axis IMU)

CONFIG_DATA_FWD_SENSOR_ADXL367

(bool) ADXL367 (3-axis accelerometer)

CONFIG_DATA_FWD_SENSOR_BME688

(bool) BME688 (environmental)

CONFIG_DATA_FWD_EXTRA_SENSOR_BME688

(bool) Append BME688 (duplication as upsampling)

Extend streamed samples with temperature, humidity, and pressure from BME688 at its native rate by upsampling (repeating the latest reading between fetches).

Adapting the sample for other boards

To run the sample on a board that is not listed in sample.yaml, add a devicetree overlay for that board target. See the following guides for the general workflow:

For this sample, you typically need to:

  1. Add a board overlay under boards/<board>_<soc>_<variant>.overlay.

  2. Configure or enable the required sensor device tree nodes (bmi270, adxl367, bme688, or your own sensor).

  3. When using UART transport, set the ncs,data-forwarder-uart chosen node to the UART used for data forwarding and assign a separate console output (for example, RTT or another UART).

  4. Update sample.yaml with the new board target when adding official support.

Adapting the sample for other sensors

To forward data from a sensor that is not supported out of the box, implement the sensor wrapper API:

Sensor wrapper

Use src/sensor/bmi270.c, src/sensor/adxl367.c, or src/sensor/bme688.c as references. Then:

  1. Add a new config DATA_FWD_SENSOR_* entry to the DATA_FWD_SENSOR option in Kconfig.

  2. Add the source file to CMakeLists.txt under the corresponding CONFIG_DATA_FWD_SENSOR_* block.

  3. Set a CONFIG_DATA_FWD_PROTO_MAX_CHANNELS default for the new channel count in Kconfig.

Host-side setup

Complete the host-side setup for your chosen data collection workflow before building and running the sample.

The Data Forwarder Host tool decodes CBOR/COBS frames from the default sample build and is intended for use with Nordic Edge AI Lab data collection workflows.

Before running the sample, get the Data Forwarder Host tool.

Building and running

This sample can be found under samples/data_forwarder in the Edge AI Add-on folder structure.

To build the sample, follow the instructions in Building an application for your preferred building environment. See also Programming for programming steps and Testing and optimization for general information about testing and debugging in the nRF Connect SDK.

Testing

After programming the sample to your development kit, complete the following steps to test it:

  1. Connect the kit to the computer using a USB cable. The kit is assigned a serial port. Serial ports are referred to as COM ports on Windows, /dev/ttyACM devices on Linux, and /dev/tty devices on macOS. To list Nordic Semiconductor devices connected to your computer together with their serial ports, open a terminal and run the nrfutil device list command. Alternatively, check your operating system’s device manager or its equivalent.

  2. Open an RTT viewer (for example, in nRF Connect for VS Code extension) to view console output. After programming, you should see output similar to the following:

    transport: BLE NUS transport ready
data_forwarder: Data forwarder started (sid 8779774)
transport: BLE connected

Collecting data on the host

Use one of the following workflows to capture sensor data on your host computer:

The Data Forwarder Host tool decodes CBOR/COBS frames from the default sample build and is intended for use with Nordic Edge AI Lab data collection workflows.

To collect data with the default configuration:

  1. Run Data Forwarder Host tool on the host computer and connect to the device over Bluetooth LE.

    Alternatively, if the host has no suitable Bluetooth LE adapter, use a second development kit running the Nordic central UART sample as a serial bridge. Flash Central UART on the second kit, wait for it to connect to the peripheral, then connect the host tool to the Central UART USB serial port.

  2. Enter a label and start a sampling session. For details refer to the Data Forwarder Host tool documentation.

Dependencies

This sample uses the following nRF Connect SDK libraries:

This sample uses the following Zephyr libraries:

The data forwarder protocol uses the following Zephyr libraries: