AP_UROS: add micro-ROS client

[srmainwaring]

A draft PR to investigate using the micro-ROS client library directly as an alternative to AP_DDS.

See: #23424 and the comment on the micro-ROS PoC.

Dependencies

The PR adds a module containing pre-built instances of the micro-ROS client library for various target platforms.

• https://github.com/srmainwaring/ardupilot_uros

This is to separate out the fairly complex process of configuring and building the client libraries. Including this step directly in the waf build would add a dependency on colcon and ROS.

Features

The AP_UROS library is feature compatible with AP_DDS. This means it can be used as a drop in replacement for AP_DDS for external control.

• publish all topics supported by AP_DDS
• arm motors and mode switch services enabled
• external control and odometry enabled

In addition there is a prototype parameter server. This is not yet integrated with ArduPilot's parameter system.

micro-ROS links

The following micro-ROS tutorials describe the process of creating the client libraries:

• Creating custom static micro-ROS library
• How to include a custom ROS message in micro-ROS
• Creating custom micro-ROS transports
• Middleware Configuration

Tasks

• Fully document process for building the client libraries for each platform (Ubuntu, macOS, stm32, esp32, ).
• Remove hardcoded platform target in AP_UROS wscript.
• Factor out common code with AP_DDS.
• Remove hardcoded flags from ardupilot_sitl CMakeLists.txt.

Notes

• The file and type names of the generated bindings and headers for DDS and UROS are not compatible, so only one of --enable-dds or --enable-uros may be selected at a time (you would not want to use them concurrently in any case).
• The accessors to the message and service interfaces for DDS and UROS are almost compatible, except for the treatment of strings and arrays. This means it should be possible to factor out common code for responding to services requests and publishing and subscribing to topics.

Testing

See the library README for build instructions.

The off-board navigation example described in ArduPilot/ardupilot_ros#11 may be run using AP_UROS instead of AP_DDS.

Figure: MAVProxy console output from SITL running with --enable-uros.

Flash

Flash usage for MatekH743 in different configurations (expand for details)

$ ./waf configure --board MatekH743
$ ./waf copter 

BUILD SUMMARY
Build directory: /Users/rhys/Code/ardupilot/ardupilot/build/MatekH743
Target          Text (B)  Data (B)  BSS (B)  Total Flash Used (B)  Free Flash (B)  External Flash Used (B)
----------------------------------------------------------------------------------------------------------
bin/arducopter   1593784      3628   258648               1597412          106516  Not Applicable      

$ ./waf configure --board MatekH743 --enable-uros
$ ./waf copter 

BUILD SUMMARY
Build directory: /Users/rhys/Code/ardupilot/ardupilot/build/MatekH743
Target          Text (B)  Data (B)  BSS (B)  Total Flash Used (B)  Free Flash (B)  External Flash Used (B)
----------------------------------------------------------------------------------------------------------
bin/arducopter   1686908      9500   252828               1696408            7512  Not Applicable 

$ ./waf configure --board MatekH743 --enable-dds
$ ./waf copter 

BUILD SUMMARY
Build directory: /Users/rhys/Code/ardupilot/ardupilot/build/MatekH743
Target          Text (B)  Data (B)  BSS (B)  Total Flash Used (B)  Free Flash (B)  External Flash Used (B)
----------------------------------------------------------------------------------------------------------
bin/arducopter   1622680      3628   258648               1626308           77620  Not Applicable   

Scripting disabled:

$ ./waf configure --board MatekH743 --disable-scripting
$ ./waf copter 

BUILD SUMMARY
Build directory: /Users/rhys/Code/ardupilot/ardupilot/build/MatekH743
Target          Text (B)  Data (B)  BSS (B)  Total Flash Used (B)  Free Flash (B)  External Flash Used (B)
----------------------------------------------------------------------------------------------------------
bin/arducopter   1449856      3508   258768               1453364          250560  Not Applicable   

$ ./waf configure --board MatekH743 --disable-scripting --enable-uros
$ ./waf copter 

BUILD SUMMARY
Build directory: /Users/rhys/Code/ardupilot/ardupilot/build/MatekH743
Target          Text (B)  Data (B)  BSS (B)  Total Flash Used (B)  Free Flash (B)  External Flash Used (B)
----------------------------------------------------------------------------------------------------------
bin/arducopter   1543492      9384   252940               1552876          151056  Not Applicable  

$ ./waf configure --board MatekH743 --disable-scripting --enable-dds
$ ./waf copter 

BUILD SUMMARY
Build directory: /Users/rhys/Code/ardupilot/ardupilot/build/MatekH743
Target          Text (B)  Data (B)  BSS (B)  Total Flash Used (B)  Free Flash (B)  External Flash Used (B)
----------------------------------------------------------------------------------------------------------
bin/arducopter   1478736      3508   258768               1482244          221680  Not Applicable

[srmainwaring]

Factor out common code

AP_UROS and AP_DDS have common code for publishing topics, handling subscriptions and services, and managing external odometry and control. This can be factored out into a common library AP_ROS which uses templated accessors to handle the different conventions in DDS and micro-ROS for strings and sequences. The AP_DDS and AP_UROS libraries provide template specialisations for the templated accessors and then use the templated versions of the common code to implement functions that would otherwise be duplicated.

This PR demonstrates the approach.

• AP_UROS: factor out common ROS client code #25179

The templates for type access are in AP_ROS_TypeConversions:

// string accessor templates
template <typename S>
const char* string_data(const S* str);

template <typename S>
const char* string_data(const S& str);

// sequence accessor templates
// see: https://stackoverflow.com/questions/15911890/overriding-return-type-in-function-template-specialization

template <typename T>
uint32_t transforms_size(const T& msg);

template <typename T>
struct transforms_type{ typedef T* type; };

template <typename T>
typename transforms_type<T>::type transforms_data(const T& msg);

With example usage in AP_ROS_ExternalOdometry, for seqeunces:

    for (size_t i = 0; i < transforms_size<TFMessage>(msg); i++) {
        const auto& ros_transform_stamped = transforms_data<TFMessage>(msg)[i];
        if (!is_odometry_frame(ros_transform_stamped)) {
            continue;
        }

and for strings:

template <typename TransformStamped>
bool AP_ROS_External_Odom::is_odometry_frame(const TransformStamped& msg)
{
    char odom_parent[] = "odom";
    char odom_child[] = "base_link";
    // Assume the frame ID's are null terminated.
    return (strcmp(string_data(msg.header.frame_id), odom_parent) == 0) &&
           (strcmp(string_data(msg.child_frame_id), odom_child) == 0);
}