added documentation and update release_note.rst

controller_manager/doc/userdoc.rst

@@ -87,6 +87,18 @@ update_rate (mandatory; integer)
   Name of a plugin exported using ``pluginlib`` for a controller.
   This is a class from which controller's instance with name "``controller_name``" is created.
 
+<controller_name>.params_file
+  The absolute path to the YAML file with parameters for the controller.
+  The file should contain the parameters for the controller in the standard ROS 2 YAML format.
+
+<controller_name>.fallback_controllers
+  List of controllers that are activated as a fallback strategy, when the spawned controllers fail by returning ``return_type::ERROR`` during the ``update`` cycle.
+  It is recommended to add all the controllers needed for the fallback strategy to the list, including the chainable controllers whose interfaces are used by the main fallback controllers.
+
+.. warning::
+  The fallback controllers activation is subject to the availability of the state and command interfaces at the time of activation.
+  It is recommended to test the fallback strategy in simulation before deploying it on the real robot.
+
 Handling Multiple Controller Managers
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

doc/release_notes.rst

@@ -26,6 +26,7 @@ For details see the controller_manager section.
 * With (`#1683 <https://github.com/ros-controls/ros2_control/pull/1683>`_) the ``rclcpp_lifecycle::State & get_state()`` and ``void set_state(const rclcpp_lifecycle::State & new_state)`` are replaced by ``rclcpp_lifecycle::State & get_lifecycle_state()`` and ``void set_lifecycle_state(const rclcpp_lifecycle::State & new_state)``. This change affects controllers and hardware. This is related to (`#1240 <https://github.com/ros-controls/ros2_control/pull/1240>`_) as variant support introduces ``get_state`` and ``set_state`` methods for setting/getting state of handles.
 * The ``assign_interfaces`` and ``release_interfaces`` methods are now virtual, so that the user can override them to store the interfaces into custom variable types, so that the user can have the flexibility to take the ownership of the loaned interfaces to the controller (`#1743 <https://github.com/ros-controls/ros2_control/pull/1743>`_)
 * The new ``PoseSensor`` semantic component provides a standard interface for hardware providing cartesian poses (`#1775 <https://github.com/ros-controls/ros2_control/pull/1775>`_)
+* The controllers now support the fallback controllers (a list of controllers that will be activated, when the spawned controllers fails by throwing an exception or returning ``return_type::ERROR`` during the ``update`` cycle) (`#1789 <https://github.com/ros-controls/ros2_control/pull/1789>`_)
 
 controller_manager
 ******************