View Source Use on Nerves

rclex can be operated onto Nerves. In this case, you do not need to prepare the ROS 2 environment on the host computer to build Nerves project (so awesome!).

This doc shows the steps on how to use Rclex on Nerves from scratch.

We have also published the Nerves project that has been prepared and includes example code at b5g-ex/rclex_on_nerves. Please also refer to this repository.

Supported Targets

Currently, we have confirmed the following boards as the Nerves device that can operate Rclex (good luck to get one!).

The below is the supported ROS 2 distribution and architecture that can operate rclex_on_nerves. The "support" colomn refers to its status of official support as the ROS 2 distribution.

Preliminaries

During the procedure for Rclex on Nerves, the docker command is used to copy the necessary directory in mix rclex.prep.ros2. Please install Docker Desktop or Docker Engine, and start it first.
And also, Rclex on Nerves will deploy an docker container for arm64 arch. If you want to operate this project by Docker Engine on other platforms (x86_64), you need to install qemu as the follows: sudo apt-get install qemu binfmt-support qemu-user-static

It should be noted that do not perform the following steps inside a docker container.
Once again, they can be operated even if ROS 2 is not installed on the host machine!

Procedure

Target device

The following steps assume that rpi4 and arm64v8 will be used as the target Nerves device. You may change the values of MIX_TARGET and --arch to match the "tag" and "arch" columns on the supported target list according to the board you want to use.

Create Nerves Project

mix nerves.new rclex_usage_on_nerves --target rpi4
cd rclex_usage_on_nerves
export MIX_TARGET=rpi4
mix deps.get

Note

If mix deps.get failed, you may need to create SSH key and configure config/target.exs.

Install rclex

rclex is available in Hex.

You can install this package into your project by adding rclex to your list of dependencies in mix.exs:

  defp deps do
    [
      ...
      {:rclex, "~> 0.10.0"},
      ...
    ]
  end

After that, execute mix deps.get into the project repository.

mix deps.get

Prepare ROS 2 resources

Note

In the following steps, Humble Hawksbill (humble) is assumed to be used as ROS_DISTRO (strongly recommend to use). If you want to use foxy or galactic, you need to replace it appropriately in the subsequent steps. Note that these have already reached EOL.

The following command extracts the ROS 2 Docker image and copies resources required for Rclex to the Nerves file system. You may change the value of --arch according to the architecture of your target board (see the "arch" column on the supported target list)

export ROS_DISTRO=humble
mix rclex.prep.ros2 --arch arm64v8

Note

The following warning messages will occur at several times when the host and target architectures are different. These can be ignored.

WARNING: The requested image's platform (linux/arm/v7) does not match the detected host platform (linux/amd64) and no specific platform was requested

Configure ROS 2 message types you want to use

Rclex provides pub/sub based topic communication using the message type defined in ROS 2. Please refer here for more details about message types in ROS 2.

The message types you want to use in your project can be specified in ros2_message_types in config/config.exs. Multiple message types can be specified separated by comma ,.

The following config/config.exs example wants to use String type.

config :rclex, ros2_message_types: ["std_msgs/msg/String"]

Then, execute the following Mix task to generate required definitions and files for message types.

mix rclex.gen.msgs

If you want to change the message types in config, do mix rclex.gen.msgs again.

Copy erlinit.config to rootfs_overlay/etc and add LD_LIBRARY_PATH

Copy erlinit.config from nerves_system_***.

cp deps/nerves_system_rpi4/rootfs_overlay/etc/erlinit.config rootfs_overlay/etc

Add LD_LIBRARY_PATH line like following.
ROS_DISTRO should be written directly such as humble, as the below.

# Enable UTF-8 filename handling in Erlang and custom inet configuration
-e LANG=en_US.UTF-8;LANGUAGE=en;ERL_INETRC=/etc/erl_inetrc

# Enable crash dumps (set ERL_CRASH_DUMP_SECONDS=0 to disable)
-e ERL_CRASH_DUMP=/root/erl_crash.dump;ERL_CRASH_DUMP_SECONDS=5

# add for ROS 2 (rclex_on_nerves)
-e LD_LIBRARY_PATH=/opt/ros/humble/lib

Why add LD_LIBRARY_PATH explicitly

ROS 2 needs the path. If you want to know the details, please read following

• https://github.com/ros-tooling/cross_compile/issues/363
• https://github.com/ros2/rcpputils/pull/122

Note

If you want to use galactic, adding line should be as the below.

## only galactic needs /opt/ros/galactic/lib/aarch64-linux-gnu also, for libddsc
# -e LD_LIBRARY_PATH=/opt/ros/galactic/lib/aarch64-linux-gnu:/opt/ros/galactic/lib

Write Rclex code

Now, you can acquire the environment for Rclex API! Of course, you can execute APIs on IEx directly.

Here is the simplest implementation example lib/rclex_usage_on_nerves.ex that will publish the string to /chatter topic.

defmodule RclexUsageOnNerves do
  alias Rclex.Pkgs.StdMsgs

  def publish_message do
    Rclex.start_node("talker")
    Rclex.start_publisher(StdMsgs.Msg.String, "/chatter", "talker")

    data = "Hello World from Rclex!"
    msg = struct(StdMsgs.Msg.String, %{data: data})

    IO.puts("Rclex: Publishing: #{data}")
    Rclex.publish(msg, "/chatter", "talker")
  end
end

Please also check the examples for Rclex.

• rclex/rclex_examples
• b5g-ex/rclex_on_nerves

Create fw, and burn (or, upload)

mix firmware
mix burn # or, mix upload

Execute

Connect the Nerves device via ssh.

ssh nerves.local

Operate the following command on IEx.

iex()> RclexUsageOnNerves.publish_message
Rclex: Publishing: Hello World from Rclex!
:ok

You can confirm the above operation by subscribing with ros2 topic echo on the machine where ROS 2 env has been installed.

$ source /opt/ros/humble/setup.bash
$ ros2 topic echo /chatter std_msgs/msg/String
data: Hello World from Rclex!
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