# Testing with DDS/micro-Ros

## Architecture

Ardupilot contains the DDS Client library, which can run as SITL. Then, the DDS application runs a ROS2 node, an EProsima Integration Service, and the MicroXRCE Agent. The two systems communicate over serial, which is the only supported protocol in Ardupilot MicroXCE DDS at this time.

```mermaid
---
title: Hardware Serial Port Loopback
---
graph LR

  subgraph Linux Computer

    subgraph Ardupilot SITL
      veh[sim_vehicle.py] <--> xrceClient[EProsima Micro XRCE DDS Client]
      xrceClient <--> port1[devUSB1]
    end

    subgraph DDS Application
      ros[ROS2 Node] <--> agent[Micro ROS Agent]
      agent <--> port2[devUSB2]
    end

    port1 <--> port2

  end
```

Currently, serial is the only supported transport, but there are plans to add IP-based transport over ethernet. 

## Installing Build Dependencies

While DDS support in Ardupilot is mostly through git submodules, another tool needs to be available on your system: Micro XRCE DDS Gen.

- Go to a directory on your system to clone the repo (perhaps next to `ardupilot`)
- Install java
  ```console
  sudo apt install default-jre
  ````
- Follow instructions [here](https://micro-xrce-dds.docs.eprosima.com/en/latest/installation.html#installing-the-micro-xrce-dds-gen-tool) to install the latest version of the generator using Ardupilot's mirror
  ```console
  git clone --recurse-submodules https://github.com/ardupilot/Micro-XRCE-DDS-Gen.git
  cd Micro-XRCE-DDS-Gen
  ./gradlew assemble
  ```

- Add the generator directory to $PATH. 
  ```console
  # Add this to ~/.bashrc

  export PATH=$PATH:/your/path/to/Micro-XRCE-DDS-Gen/scripts
  ```
- Test it
  ```console
  cd /path/to/ardupilot
  microxrceddsgen -version
  # openjdk version "11.0.18" 2023-01-17
  # OpenJDK Runtime Environment (build 11.0.18+10-post-Ubuntu-0ubuntu122.04)
  # OpenJDK 64-Bit Server VM (build 11.0.18+10-post-Ubuntu-0ubuntu122.04, mixed mode, sharing)
  # microxrceddsgen version: 1.0.0beta2
  ```

> :warning: **If you have installed FastDDS or FastDDSGen globally on your system**:
eProsima's libraries and the packaging system in Ardupilot are not determistic in this scenario.
You may experience the wrong version of a library brought in, or runtime segfaults.
For now, avoid having simultaneous local and global installs.
If you followed the [global install](https://fast-dds.docs.eprosima.com/en/latest/installation/sources/sources_linux.html#global-installation)
section, you should remove it and switch to local install.

## Setup serial for SITL with DDS

On Linux, creating a virtual serial port will be necessary to use serial in SITL, because of that install socat.

```
sudo apt-get update
sudo apt-get install socat
```

## Setup ardupilot for SITL with DDS

Set up your [SITL](https://ardupilot.org/dev/docs/setting-up-sitl-on-linux.html).
Run the simulator with the following command. Take note how two parameters need adjusting from default to use DDS.
| Name | Description |
| - | - |
| SERIAL1_BAUD | The serial baud rate for DDS |
| SERIAL1_PROTOCOL | Set this to 45 to use DDS on the serial port |
```bash
# Wipe params till you see "AP: ArduPilot Ready"
# Select your favorite vehicle type
sim_vehicle.py -w -v ArduPlane

# Set params
param set SERIAL1_BAUD 115
# See libraries/AP_SerialManager/AP_SerialManager.h AP_SerialManager SerialProtocol_DDS_XRCE
param set SERIAL1_PROTOCOL 45
```
## Setup ROS 2 and micro-ROS

Follow the steps to use the microROS Agent

- Install ROS Humble (as described here)

  - https://docs.ros.org/en/humble/Installation/Ubuntu-Install-Debians.html

- Install and run the microROS agent (as descibed here). Make sure to use the `humble` branch.
  - Follow [the instructions](https://micro.ros.org/docs/tutorials/core/first_application_linux/) for the following:

    - Do "Installing ROS 2 and the micro-ROS build system"
      - Skip the docker run command, build it locally instead
    - Skip "Creating a new firmware workspace"
    - Skip "Building the firmware"
    - Do "Creating the micro-ROS agent"
    - Source your ROS workspace

Until this [PR](https://github.com/micro-ROS/micro-ROS.github.io/pull/401) is merged, ignore the notes about `foxy`. It works on `humble`.

## Using the ROS2 CLI to Read Ardupilot Data

After your setups are complete, do the following:

- Source the ros2 installation
  ```bash
  source /opt/ros/humble/setup.bash
  ```
- Start a virtual serial port with socat. Take note of the two `/dev/pts/*` ports. If yours are different, substitute as needed.
  ```bash
  socat -d -d pty,raw,echo=0 pty,raw,echo=0
  >>> 2023/02/21 05:26:06 socat[334] N PTY is /dev/pts/1
  >>> 2023/02/21 05:26:06 socat[334] N PTY is /dev/pts/2
  >>> 2023/02/21 05:26:06 socat[334] N starting data transfer loop with FDs [5,5] and [7,7]
  ```
- Run the microROS agent
  ```bash
  cd ardupilot/libraries/AP_DDS
  ros2 run micro_ros_agent micro_ros_agent serial -b 115200 -D /dev/pts/2  -r dds_xrce_profile.xml # (assuming we are using tty/pts/2 for DDS Application)
  ```
- Run SITL (remember to kill any terminals running ardupilot SITL beforehand)
  ```bash
  sim_vehicle.py -v ArduPlane -D --console --enable-dds -A "--uartC=uart:/dev/pts/1" # (assuming we are using /dev/pts/1 for Ardupilot SITL)
  ```
- You should be able to see the agent here and view the data output.
  ```bash
  $ ros2 node list
  /Ardupilot_DDS_XRCE_Client

  $ ros2 topic list  -v
  Published topics:
   * /ROS2_NavSatFix0 [sensor_msgs/msg/NavSatFix] 1 publisher
   * /ROS2_Time [builtin_interfaces/msg/Time] 1 publisher
   * /parameter_events [rcl_interfaces/msg/ParameterEvent] 1 publisher
   * /rosout [rcl_interfaces/msg/Log] 1 publisher
   * /tf [tf2_msgs/msg/TFMessage] 1 publisher

  Subscribed topics:

  $ ros2 topic hz /ROS2_Time
  average rate: 50.115
          min: 0.012s max: 0.024s std dev: 0.00328s window: 52

  $ ros2 topic echo /ROS2_Time 
  sec: 1678668735
  nanosec: 729410000
  ---
  ```

  The static transforms for enabled sensors are also published, and can be recieved like so:
  ```console
  ros2 topic echo /tf --qos-depth 1 --qos-history keep_last --qos-reliability reliable --qos-durability transient_local --once
  ```
  In order to consume the transforms, it's highly recommended to [create and run a transform broadcaster in ROS 2](https://docs.ros.org/en/humble/Concepts/About-Tf2.html#tutorials). 

## Adding DDS messages to Ardupilot

Unlike the use of ROS 2 `.msg` files, since Ardupilot supports native DDS, the message files follow [OMG IDL DDS v4.2](https://www.omg.org/spec/IDL/4.2/PDF).
This package is intended to work with any `.idl` file complying with those extensions.

Over time, these restrictions will ideally go away. 

To get a new IDL file from ROS2, follow this process:
```console
cd ardupilot
source /opt/ros/humble/setup.bash
# Find the IDL file
find /opt/ros/$ROS_DISTRO -type f -wholename \*builtin_interfaces/msg/Time.idl
# Create the directory in the source tree if it doesn't exist similar to the one found in the ros directory
mkdir -p libraries/AP_DDS/Idl/builtin_interfaces/msg/
# Copy the IDL
cp /opt/ros/humble/share/builtin_interfaces/msg/Time.idl libraries/AP_DDS/Idl/builtin_interfaces/msg/
# Build the code again with the `--enable-dds` flag as described above 
```