Update rtde client documentation

Author: urfeex

doc/architecture.rst

@@ -17,6 +17,7 @@ fully functioning robot interface. For details on how to use it, please see the
    :maxdepth: 1
 
    architecture/script_sender
+   architecture/rtde_client
 
 The ``UrDriver``'s modules will be explained in the following.
 

doc/architecture/rtde_client.rst

@@ -0,0 +1,63 @@
+RTDEClient
+==========
+
+The ``RTDEClient`` class serves as a standalone
+`RTDE <https://www.universal-robots.com/articles/ur-articles/real-time-data-exchange-rtde-guide/>`_
+client. To use the RTDE-Client, you'll have to initialize and start it separately:
+
+.. code-block:: c++
+
+   rtde_interface::RTDEClient my_client(ROBOT_IP, notifier, OUTPUT_RECIPE, INPUT_RECIPE);
+   my_client.init();
+   my_client.start();
+   while (true)
+   {
+     std::unique_ptr<rtde_interface::DataPackage> data_pkg = my_client.getDataPackage(READ_TIMEOUT);
+     if (data_pkg)
+     {
+       std::cout << data_pkg->toString() << std::endl;
+     }
+   }
+
+Upon construction, two recipe files have to be given, one for the RTDE inputs, one for the RTDE
+outputs. Please refer to the `RTDE
+guide <https://www.universal-robots.com/articles/ur-articles/real-time-data-exchange-rtde-guide/>`_
+on which elements are available.
+
+Inside the ``RTDEclient`` data is received in a separate thread, parsed by the ``RTDEParser`` and
+added to a pipeline queue.
+
+Right after calling ``my_client.start()``, it should be made sure to read the buffer from the
+``RTDEClient`` by calling ``getDataPackage()`` frequently. The Client's queue can only contain a
+restricted number of items at a time, so a ``Pipeline producer overflowed!`` error will be raised if the buffer isn't read frequently enough.
+
+For writing data to the RTDE interface, use the ``RTDEWriter`` member of the ``RTDEClient``. It can be
+retrieved by calling ``getWriter()`` method. The ``RTDEWriter`` provides convenience methods to write
+all data available at the RTDE interface. Make sure that the required keys are configured inside the
+input recipe, as otherwise the send-methods will return ``false`` if the data field is not setup in
+the recipe.
+
+An example of a standalone RTDE-client can be found in the ``examples`` subfolder. To run it make
+sure to
+
+* have an instance of a robot controller / URSim running at the configured IP address (or adapt the
+  address to your needs)
+* run it from the package's main folder, as for simplicity reasons it doesn't use any sophisticated
+  method to locate the required files.
+
+.. note::
+   The ``URDriver`` class creates a ``RTDEClient`` during initialization using the provided
+   recipes and utilizing the robot model's maximum frequency. If you would like to use a different
+   frequency, please use the ``resetRTDEClient()`` method after the ``UrDriver`` object has been
+   created.
+
+RTDEWriter
+----------
+
+The ``RTDEWriter`` class provides an interface to write data to the RTDE interface. Data fields that
+should be written have to be defined inside the ``INPUT_RECIPE`` as noted above.
+
+The class offers specific methods for every RTDE input possible to write.
+
+Data is sent asynchronously to the RTDE interface.
+