Notes on converting player code to ROS


BUILD TREE
----------

ROS code is organized into stacks and packages.  Stacks are
subdirectories in the tree with package directories inside them.  Each
stack or package has a global name in the ROS package name space, so
their directory names need to be unique and descriptive.

A stack directory is identified by its <stack.xml> file.  The rosstack
command should be able to find and print information about it.

  http://www.ros.org/wiki/Stacks/CreateStack?highlight=(stack)|(creating)

A package directory is identified by a manifest.xml file describing
its name, authors, licences, exports and dependencies.  Once that file
exists, the rospack command should be able to find and print
information about it.

  http://www.ros.org/wiki/ROS/Tutorials/CreatingPackage?highlight=(BeginnerCategory)

Remove any old SConscript files, they are replaced by CMakeLists.txt
in the ROS build scheme.  You should be able to build any package
using the rosmake command.

  http://www.ros.org/wiki/ROS/BuildSystemUsage


DRIVERS
-------

Convert player drivers to ROS nodes.  The class inherited from the
player Driver class is no longer needed and just adds unnecessary
complexity.  

Make a simple C++ main program, something like this:

  int main(int argc, char** argv)
  {
    ros::init(argc, argv, NODE);
    ros::NodeHandle node;
  
    // topics to read and write
    brake_cmd = node.subscribe(NODE "/cmd", 10, ProcessCommand,
                               ros::TransportHints().tcpNoDelay(true));
    brake_state = node.advertise<art_brake::State>(NODE "/state", 10);
  
    if (GetParameters() != 0)             // from the player constructor
      return 1;
  
    ros::Rate cycle(HERTZ_BRAKE);         // set driver cycle rate
  
    if (Setup() != 0)                     // from the player Setup()
      return 2;
  
    // Main loop; grab messages off our queue and republish them via ROS
    while(ros::ok())
      {
        ...                               // activities from player Main()
        cycle.sleep();                    // sleep until next cycle
      }
  
    Shutdown();
  
    return 0;
  }



INTERFACES
----------

Most player interfaces have ROS equivalents, here are some examples.
The player code snippet is shown first, followed by an indented ROS
version, with comments (where appropriate).


ART_ERROR(msg);

  ROS_ERROR(msg) or ROS_FATAL(msg), depending on severity.

ART_MSG(level, msg);

  ROS_INFO(msg) if infrequent, or ROS_DEBUG(msg) if recurring

  The verbose configuration parameter is not needed.  Use
  rxloggerlevel command to turn debug output on or off dynamically at
  run time.  Much nicer.

ART_WARN(msg);

  ROS_WARN(msg);

DTOR(deg);

  angles::from_degees(deg);

  // This requires adding <depend package="angles"/> to your
  // manifest.xml, then adding #include <angles/angles.h> to the source
  // file.

extern PlayerTime* GlobalTime;
GlobalTime->GetTimeDouble(&time);

  double time = ros::Time::now().toSec();

// main loop
for(;;)
  {
    // see if we are supposed to exit
    pthread_testcancel();
    ...

  // main loop
  while(ros::ok())
    {
      ...

PLAYER_ERROR(msg);

  ROS_ERROR(msg) or ROS_FATAL(msg), depending on severity.

PLAYER_MSGn(level, msg);

  ROS_INFO(msg) if infrequent, or ROS_DEBUG(msg) if recurring

PLAYER_WARN(msg);

  ROS_WARN(msg);

const char *port;                       // tty port name
port = cf->ReadString(section, "port", "/dev/null");
PLAYER_MSG1(2, CLASS " constructor: brake port = %s", port);

  // use private node handle to get parameters
  ros::NodeHandle mynh("~");
  std::string port;                     // tty port name

  if (!mynh.getParam("port", port))
      port = "/dev/null";
  ROS_INFO("brake port = %s", port.c_str());


RTOD(rad);

  angles::to_degrees(rad);

  // See DTOR() for dependencies.