Propose generic messages for commanding and getting states from controllers. (backport #69)

control_msgs/CMakeLists.txt

@@ -30,7 +30,11 @@ set(msg_files
   msg/JointTolerance.msg
   msg/JointTrajectoryControllerState.msg
   msg/MecanumDriveControllerState.msg
+  msg/MultiDOFCommand.msg
+  msg/MultiDOFStateStamped.msg
   msg/PidState.msg
+  msg/SingleDOFState.msg
+  msg/SingleDOFStateStamped.msg
   msg/SteeringControllerStatus.msg
 )
 

control_msgs/msg/JointControllerState.msg

@@ -1,5 +1,7 @@
 # This message presents current controller state of one joint.
 
+# It is deprecated as of Humble in favor of SingleDOFStateStamped.msg
+
 # Header timestamp should be update time of controller state
 std_msgs/Header header
 

control_msgs/msg/MultiDOFCommand.msg

@@ -0,0 +1,13 @@
+# The message defines command for multiple degrees of freedom (DoF) typically used by many controllers.
+# The message intentionally avoids 'joint' nomenclature because it can be generally use for command with
+# different semantic meanings, e.g., joints, Cartesian axes, or have abstract meaning like GPIO interface.
+
+# names of degrees of freedom
+string[] dof_names
+
+# values used by most of the controller
+float64[] values
+
+# First derivation of the values, e.g., velocity if values are positions.
+# This is useful for PID and similar controllers.
+float64[] values_dot

control_msgs/msg/MultiDOFStateStamped.msg

@@ -0,0 +1,6 @@
+# This message presents current controller state of multiple degrees of freedom.
+
+# Header timestamp should be update time of controller state
+std_msgs/Header header
+
+SingleDOFState[] dof_states

control_msgs/msg/SingleDOFState.msg

@@ -0,0 +1,25 @@
+# This message presents current controller state of one degree of freedom.
+
+# DoF name, e.g., joint or Cartesian axis name
+string name
+
+# The set point, that is, desired state.
+float64 reference
+
+# Current value of the process (ie: latest sensor measurement on the controlled value).
+float64 feedback
+
+# First time-derivative of the process value. E.g., velocity.
+float64 feedback_dot
+
+# The error of the controlled value, essentially process_value - set_point (for a regular PID implementation).
+float64 error
+
+# First time-derivative of the error of the controlled value.
+float64 error_dot
+
+# Time between two consecutive updates/execution of the control law.
+float64 time_step
+
+# Current output of the controller.
+float64 output

control_msgs/msg/SingleDOFStateStamped.msg

@@ -0,0 +1,6 @@
+# This message presents current controller state of one degree of freedom.
+
+# Header timestamp should be update time of controller state
+std_msgs/Header header
+
+SingleDOFState dof_state