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NetworkCommunication.md

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Network communication (using FLNL)

Purpose

libFLNL and the FLNLHelper class can be used to established a TCP/IP communication between CORC (server) and a client. It is intended to:

  • Publish the robot state, typically at the frequency of the controller
  • Send and receive short commands with double value parameters

Usage

To use it in a CORC state machine:

  • Declare an FLNLHelper in your state machine class: std::shared_ptr<FLNLHelper> UIserver = nullptr;
  • Instantiate and initialise it in the derived State Machine init method:
	UIserver = std::make_shared<FLNLHelper>("192.168.7.2");       //Instantiate object and open communication (waiting for client to connect). IP adress is server address to listen on.

	UIserver->registerState(myTime);                          //Reference to a time value (double)
	UIserver->registerState(robot->getEndEffPositionRef());   //Reference to an Eigen vector
	UIserver->registerState(myStdVector);                     //Reference to an std::vector<double>
  • Alternatively you can also initialise it with an helper constructor: UIserver = std::make_shared<FLNLHelper>(*robot(), "192.168.7.2"); which will automatically register the time and robot state (position, velocity and torque) to be sent at each update.
  • Call the update method to send the states over the network regularlry, typically in your hwStateUpdate method: UIserver->sendState();
  • Received command can be checked and process at any point. Example in M3DemoMachine:
bool goToTele(StateMachine & SM) {
    M3DemoMachine & sm = static_cast<M3DemoMachine &>(SM); //Cast to specific StateMachine type

    if ( sm.UIserver->isCmd("GOTL") ) {
        sm.UIserver->sendCmd(string("OKTL"));
        return true;
    }

    return false;
}
  • Similarly, commands can be sent to the client at any point: UIserver->sendCmd(string cmd, std:vector<double> param).

Examples

See M3DemoMachine for an example.

Examples of Unity-C# and Matlab clients are available here.

Important notes

Note 1: FLNL is design to accept only one client per server.

Note 2: FLNL is meant to be asynchronous and real-time: if the client and server are running at different frequencies, no buffering is performed. Only the last received command and the last received values will be available.

Note 3: Commands are currently restricted to 4 characters and only 30 values/parameters can be sent at once.

Note 4: By default the communication is established on Port 2048. This can be specified in the constructor.