ardupilot/libraries/AP_DDS/README.md

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# Testing with DDS/micro-Ros
## Architecture
Ardupilot contains the DDS Client library, which can run as SITL. Then, the DDS application runs a ROS 2 node, an eProsima Integration Service, and the MicroXRCE Agent. The two systems communicate over serial or UDP.
```mermaid
---
title: UDP Loopback
---
graph LR
subgraph Linux Computer
subgraph Ardupilot SITL
veh[sim_vehicle.py] <--> xrceClient[EProsima Micro XRCE DDS Client]
xrceClient <--> port1[udp:2019]
end
subgraph DDS Application
ros[ROS 2 Node] <--> agent[Micro ROS Agent]
agent <-->port1[udp:2019]
end
loopback
end
```
```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[ROS 2 Node] <--> agent[Micro ROS Agent]
agent <--> port2[devUSB2]
end
port1 <--> port2
end
```
## 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 deterministic 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.
### Serial Only: Set up serial for SITL with DDS
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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
```
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## 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. If using UDP, the only parameter you need to set it `DDS_ENABLE`.
| Name | Description | Default |
| - | - | - |
| DDS_ENABLE | Set to 1 to enable DDS, or 0 to disable | 1 |
| SERIAL1_BAUD | The serial baud rate for DDS | 57 |
| SERIAL1_PROTOCOL | Set this to 45 to use DDS on the serial port | 0 |
```console
# Wipe params till you see "AP: ArduPilot Ready"
# Select your favorite vehicle type
sim_vehicle.py -w -v ArduPlane --console -DG --enable-dds
# Only set this for Serial, which means 115200 baud
param set SERIAL1_BAUD 115
# See libraries/AP_SerialManager/AP_SerialManager.h AP_SerialManager SerialProtocol_DDS_XRCE
param set SERIAL1_PROTOCOL 45
```
DDS is currently enabled by default, if it's part of the build. To disable it, run the following and reboot the simulator.
```
param set DDS_ENABLE 0
REBOOT
```
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## 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 geographic_msgs
```console
sudo apt install ros-humble-geographic-msgs
```
- Install and run the microROS agent (as described here). Make sure to use the `humble` branch.
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- Follow [the instructions](https://micro.ros.org/docs/tutorials/core/first_application_linux/) for the following:
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- 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 ROS 2 CLI to Read Ardupilot Data
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After your setups are complete, do the following:
- Source the ROS 2 installation
```console
source /opt/ros/humble/setup.bash
```
Next, follow the associated section for your chosen transport, and finally you can use the ROS 2 CLI.
### UDP (recommended for SITL)
- Run the microROS agent
```console
cd ardupilot/libraries/AP_DDS
ros2 run micro_ros_agent micro_ros_agent udp4 -p 2019 -r dds_xrce_profile.xml
```
- Run SITL (remember to kill any terminals running ardupilot SITL beforehand)
```console
sim_vehicle.py -v ArduPlane -DG --console --enable-dds
```
### Serial
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- Start a virtual serial port with socat. Take note of the two `/dev/pts/*` ports. If yours are different, substitute as needed.
```console
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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
```console
cd ardupilot/libraries/AP_DDS
# assuming we are using tty/pts/2 for DDS Application
ros2 run micro_ros_agent micro_ros_agent serial -b 115200 -r dds_xrce_profile.xml -D /dev/pts/2
```
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- Run SITL (remember to kill any terminals running ardupilot SITL beforehand)
```console
# assuming we are using /dev/pts/1 for Ardupilot SITL
sim_vehicle.py -v ArduPlane -DG --console --enable-dds -A "--uartC=uart:/dev/pts/1"
```
## Use ROS 2 CLI
You should be able to see the agent here and view the data output.
```bash
$ ros2 node list
/ardupilot_dds
```
```bash
$ ros2 topic list -v
Published topics:
* /ap/battery/battery0 [sensor_msgs/msg/BatteryState] 1 publisher
* /ap/clock [rosgraph_msgs/msg/Clock] 1 publisher
* /ap/geopose/filtered [geographic_msgs/msg/GeoPoseStamped] 1 publisher
* /ap/navsat/navsat0 [sensor_msgs/msg/NavSatFix] 1 publisher
* /ap/pose/filtered [geometry_msgs/msg/PoseStamped] 1 publisher
* /ap/tf_static [tf2_msgs/msg/TFMessage] 1 publisher
* /ap/time [builtin_interfaces/msg/Time] 1 publisher
* /ap/twist/filtered [geometry_msgs/msg/TwistStamped] 1 publisher
* /parameter_events [rcl_interfaces/msg/ParameterEvent] 1 publisher
* /rosout [rcl_interfaces/msg/Log] 1 publisher
Subscribed topics:
* /ap/cmd_vel [geometry_msgs/msg/TwistStamped] 1 subscriber
* /ap/joy [sensor_msgs/msg/Joy] 1 subscriber
* /tf [tf2_msgs/msg/TFMessage] 1 subscriber
```
```bash
$ ros2 topic hz /ap/time
average rate: 50.115
min: 0.012s max: 0.024s std dev: 0.00328s window: 52
```
```bash
$ ros2 topic echo /ap/time
sec: 1678668735
nanosec: 729410000
```
```bash
$ ros2 service list
/ap/arm_motors
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/ap/mode_switch
---
```
The static transforms for enabled sensors are also published, and can be received like so:
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```bash
ros2 topic echo /ap/tf_static --qos-depth 1 --qos-history keep_last --qos-reliability reliable --qos-durability transient_local --once
```
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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).
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## Using ROS 2 services
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The `AP_DDS` libraary exposes services which are automatically mapped to ROS 2
services using appropriate naming conventions for topics and message and service
types. An earlier version of `AP_DDS` required the use of the eProsima
[Integration Service](https://github.com/eProsima/Integration-Service) to map
the request / reply topics from DDS to ROS 2, but this is no longer required.
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List the available services:
```bash
$ ros2 service list -t
/ap/arm_motors [ardupilot_msgs/srv/ArmMotors]
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/ap/mode_switch [ardupilot_msgs/srv/ModeSwitch]
```
Call the arm motors service:
```bash
$ ros2 service call /ap/arm_motors ardupilot_msgs/srv/ArmMotors "{arm: True}"
requester: making request: ardupilot_msgs.srv.ArmMotors_Request(arm=True)
response:
ardupilot_msgs.srv.ArmMotors_Response(result=True)
```
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Call the mode switch service:
```bash
$ ros2 service call /ap/mode_switch ardupilot_msgs/srv/ModeSwitch "{mode: 4}"
requester: making request: ardupilot_msgs.srv.ModeSwitch_Request(mode=4)
response:
ardupilot_msgs.srv.ModeSwitch_Response(status=True, curr_mode=4)
```
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## Contributing to `AP_DDS` library
### 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 ROS 2, follow this process:
```bash
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
```
### Rules for adding topics and services to `dds_xrce_profile.xml`
Topics and services available from `AP_DDS` are automatically mapped into ROS 2
provided a few rules are followed when defining the entries in
`dds_xrce_profile.xml`.
#### ROS 2 message and service interface types
ROS 2 message and interface definitions are mangled by the `rosidl_adapter` when
mapping from ROS 2 to DDS to avoid naming conflicts in the C/C++ libraries.
The ROS 2 object `namespace::Struct` is mangled to `namespace::dds_::Struct_`
for DDS. The table below provides some example mappings:
| ROS 2 | DDS |
| --- | --- |
| `rosgraph_msgs::msg::Clock` | `rosgraph_msgs::msg::dds_::Clock_` |
| `sensor_msgs::msg::NavSatFix` | `sensor_msgs::msg::dds_::NavSatFix_` |
| `ardupilot_msgs::srv::ArmMotors_Request` | `ardupilot_msgs::srv::dds_::ArmMotors_Request_` |
| `ardupilot_msgs::srv::ArmMotors_Response` | `ardupilot_msgs::srv::dds_::ArmMotors_Response_` |
Note that a service interface always requires a Request / Response pair.
#### ROS 2 topic and service names
The ROS 2 design article: [Topic and Service name mapping to DDS](https://design.ros2.org/articles/topic_and_service_names.html) describes the mapping of ROS 2 topic and service
names to DDS. Each ROS 2 subsytem is provided a prefix when mapped to DDS.
The request / response pair for services require an additional suffix.
| ROS 2 subsystem | DDS Prefix | DDS Suffix |
| --- | --- | --- |
| topics | rt/ | |
| service request | rq/ | Request |
| service response | rr/ | Reply |
| service | rs/ | |
| parameter | rp/ | |
| action | ra/ | |
The table below provides example mappings for topics and services
| ROS 2 | DDS |
| --- | --- |
| ap/clock | rt/ap/clock |
| ap/navsat/navsat0 | rt/ap/navsat/navsat0 |
| ap/arm_motors | rq/ap/arm_motorsRequest, rr/ap/arm_motorsReply |
Refer to existing mappings in [`dds_xrce_profile.xml`](https://github.com/ArduPilot/ardupilot/blob/master/libraries/AP_DDS/dds_xrce_profile.xml) for additional details.
### Development Requirements
Astyle is used to format the C++ code in AP_DDS. This is required for CI to pass the build.
See [Tools/CodeStyle/ardupilot-astyle.sh](../../Tools/CodeStyle/ardupilot-astyle.sh).
```bash
./Tools/CodeStyle/ardupilot-astyle.sh libraries/AP_DDS/*.h libraries/AP_DDS/*.cpp
```
Pre-commit is used for other things like formatting python and XML code.
This will run the tools automatically when you commit. If there are changes, just add them back your staging index and commit again.
1. Install [pre-commit](https://pre-commit.com/#installation) python package.
1. Install ArduPilot's hooks in the root of the repo, then commit like normal
```bash
cd ardupilot
pre-commit install
git commit
```