Introduction

Dragonfly is a simple messaging system that helps programmers create modular distributed applications rapidly. It hides the complexities of socket programming and data translation, also provides a uniform high-level API in each of the supported programming languages (C++, C#, Python, Matlab) and operating systems (Windows, Linux). Therefore, programmers are able to write each part of their application in their programming language of choice and on their operating system of choice without having to worry about how the modules will communicate with each other.

Dragonfly consists of several components: a central message exchange daemon (MessageManager), a data logger daemon (Logger), and utilities to create message definitions in all supported programming languages.

Dragonfly uses a client-server architecture where MessageManager is the central server and software modules that would like to talk to each other are the clients. MessageManager keeps a listening socket for modules to connect to and start sending messages. All messages go through MessageManager which forwards them to the connected modules based on their subscriptions. Modules connect to MessageManager, subscribe to message types they care about, send messages that will be forwarded by MessageManager to all modules that have subscribed to those message types, and receive messages that they themselves have subscribed to. The modules remain independent of each other and do not have to know which modules will consume their messages or where the messages they consume originate.

History

Dragonfly was first developed, under the name Real-Time Messaging Architecture (RTMA), by Meel Velliste and Sagi Perel for use in the development of brain-computer interface development.

Publications whose experiments utilized Dragonfly Messaging include:

• Velliste, M., Perel, S., Spalding, M. C., Whitford, A. S., & Schwartz, A. B. (2008). Cortical control of a prosthetic arm for self-feeding. Nature, 453(7198), 1098-101. doi:10.1038/nature06996
• Clanton, S. T., McMorland, A. J. C., Zohny, Z., Jeffries, S. M., Rasmussen, R. G., Flesher, S. N., & Velliste, M. (2013). Seven Degree of Freedom Cortical Control of a Robotic Arm. In C. Guger, B. Z. Allison, & G. Edlinger (Eds.), Brain-Computer Interface Research (pp. 73-81). Berlin, Heidelberg: Springer Berlin Heidelberg. doi:10.1007/978-3-642-36083-1
• Collinger, J. L., Wodlinger, B., Downey, J. E., Wang, W., Tyler-Kabara, E. C., Weber, D. J., McMorland, A. J. C., Velliste, M., Boninger, M. L., Schwartz, A. B. (2012). High-performance neuroprosthetic control by an individual with tetraplegia. The Lancet. doi:10.1016/S0140-6736(12)61816-9

Prerequisites

Bare minimum requirement is that you have a C++ compiler installed. On linux, you also need to have qt4-qmake installed (in a future release, this requirement will be eliminated). If you’d like to have support for other languages, see below further requirements:

Python

• Version >= 2.6 (python3 is currently not supported)
• Install swig >= 2.0.3 (on windows, make sure swig.exe is in PATH)
• Install ctypeslib
  • Linux: sudo apt-get install python-ctypeslib
  • Windows: Download from http://code.google.com/p/ctypesgen

C#

• Windows only, Visual Studio 2005 or later

Matlab

• Version >= 2007b
• Configure Matlab to recognize the Visual Studio C++ compiler

Installation

Linux

Clone the repository and compile the source as follows:

1. In a terminal execute the following:

    cd Dragonfly/build
    make
   

2. Create DRAGONFLY environment variable and set it to where your Dragonfly folder is

3. Copy Dragonfly/lib/libDragonfly.so to /usr/lib or add Dragonfly/lib to LD_LIBRARY_PATH (See set_env_vars.sh in `tools' folder for reference)

4. If you plan to use the matlab interface, start matlab and execute the following:

    cd Dragonfly/lang/matlab
    make
    cd Dragonfly/src/utils/LogReader
    make
   

5. If you plan to use the python interface, append Dragonfly/lang/python to PYTHONPATH environment variable (See set_env_vars.sh in `tools' folder for reference)

Windows

We recommend that you use the installer provided in the binaries repo which contains ready-to-use executables and will also set the necessary environment variables automatically.

If you'd like to compile from source, clone the repository and follow these instructions:

1. Build Dragonfly/build/Dragonfly.sln with Visual Studio (2005 or later)

2. Create DRAGONFLY environment variable and set it to where your Dragonfly folder is

3. If you plan to use the python interface,

• Set PYTHON_LIB environment variable (ex: C:\Python27\libs)
• Set PYTHON_INCLUDE environment variable (ex: C:\Python27\include)
• Build Dragonfly/lang/python/PyDragonfly.sln with Visual Studio (2005 or later)
• Add %DRAGONFLY%\lang\python to PYTHONPATH environment variable

4. If you plan to use the Matlab interface, start matlab and execute the following:

    cd Dragonfly/lang/matlab
    make
    cd Dragonfly/src/utils/LogReader
    make
   

Directory Organization

• bin
  executable modules
• build
  source code build scripts
• examples
  example programs showing how to use Dragonfly
• include
  include files for the C++ API
• lang
  APIs for other languages
• lib
  library files for the C++ API
• src
  source code for C++ API and executable modules
• tools
  scripts for creating installers and generating message definition files

API Summary

• ConnectToMMM(ModuleID, ServerAddress)
• DisconnectFromMMM()
• Subscribe(MessageType)
• Unsubscribe(MessageType)
• ReadMessage(Timeout)
• SendMessage(MessageType, MessageData)
• SendSignal(MessageType)

Example Code

Dragonfly/examples folder contains ready to run modules in all supported languages. See the README.txt file in each example folder for further information.

Creating Message Definitions

Dragonfly uses standard C header files to describe message definitions.

Each message consists of a message type and an optional message body.

The message type is an integer that should be selected to uniquely identify each message. It is set with a #define statement and the name of the message needs to begin with MT_. Here is an example:

    #define MT_ROBOT_FEEDBACK               100

The message body is a struct composed of one or more data fields which can be standard C data types and other structs. The struct has to have the same message name as the message type, and it needs to begin with MDF_. Here is an example:

    typedef struct {
      double    position;
      double    velocity;
      double    force;
    } MDF_ROBOT_FEEDBACK;        

Here is a more complex example:

    typedef struct {
        int     SerialNo;
        int     Flags;
        double  dt;
    } SAMPLE_HEADER;

    #define MAX_ROBOT_FEEDBACK_DIMS     10
    typedef struct {
      SAMPLE_HEADER sample_header;
      double        position[MAX_ROBOT_FEEDBACK_DIMS];
      double        velocity[MAX_ROBOT_FEEDBACK_DIMS];
      double        force[MAX_ROBOT_FEEDBACK_DIMS];
    } MDF_ROBOT_FEEDBACK;

The message body fields need to be manually padded for data alignment as necessary. The following is an example of how to define the fields for 64-bit alignment:

    typedef struct {
      int source_index;    		
      int reserved;        		// for 64-bit alignment
      double source_timestamp;
    } MDF_RAW_SAMPLE_RESPONSE;

If you are not sure how to align message fields on your system, it is safe to use 64-bit alignment. Even if your system is not 64-bit, or if you have a mixture of systems with different alignment requirements, this practice will ensure proper alingment.

To translate the message definitions in C header files into constructs in your choice of language, you need to process them with the appropriate build script for your language. The build scripts are located in the Dragonfly\tools folder. Python build script is written in python. Matlab and C# build scripts require Matlab. (In a future release, dependency on Matlab will be eliminated)

Matlab

    build_matlab_message_defs(path_to_message_definition_header_file)

C#

    build_dotNet_message_defs(path_to_message_definition_header_file)

Python

    build_python_message_defs(path_to_message_definition_header_file)