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tutorials:beginner:process_modules_2 [2017/07/13 15:02] – created cpotutorials:beginner:process_modules_2 [2020/09/03 10:34] (current) – [Writing a process module for the turtlesim] gkazhoya
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 **Description:** in this tutorial you will learn about CRAM process modules and write a simple one to move the turtlesim. **Description:** in this tutorial you will learn about CRAM process modules and write a simple one to move the turtlesim.
  
-**Previous Tutorial:** [[tutorials:beginner:designators|Creating action designators for the turtlesim]]\\ +**Previous Tutorial:** [[tutorials:beginner:motion_designators|Creating motion designators for the turtlesim]]\\ 
-**Next Tutorial:** [[tutorials:beginner:location_designators|Using location designators with the turtlesim]]+**Next Tutorial:** [[tutorials:beginner:assigning_actions_2|Automatically choosing a process module for a motion]]
  
 ===== Process modules: an overview ===== ===== Process modules: an overview =====
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 Once again, some new dependencies must be declared in the tutorial files you've been working on.  Once again, some new dependencies must be declared in the tutorial files you've been working on. 
  
-In your ''package.xml'' file you need to add build and runtime dependencies on ''cram_process_modules'':+In your ''package.xml'' file you need to add a dependency on ''cram_process_modules'':
  
 <code> <code>
-  <build_depend>cram_process_modules</build_depend> +  <depend>cram_process_modules</depend>
- +
-  <run_depend>cram_process_modules</run_depend>+
 </code> </code>
  
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 <code lisp> <code lisp>
-(defsystem cram-beginner-tutorial +(defsystem cram-my-beginner-tutorial 
-  :depends-on (cram-language roslisp turtlesim-msg geometry_msgs-msg cl-transforms+  :depends-on (cram-language roslisp turtlesim-msg turtlesim-srv geometry_msgs-msg cl-transforms
                              cram-designators cram-prolog                              cram-designators cram-prolog
                              cram-process-modules cram-language-designator-support)                              cram-process-modules cram-language-designator-support)
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              (:file "control-turtlesim" :depends-on ("package"))              (:file "control-turtlesim" :depends-on ("package"))
              (:file "simple-plans" :depends-on ("package" "control-turtlesim"))              (:file "simple-plans" :depends-on ("package" "control-turtlesim"))
-             (:file "action-designators" :depends-on ("package"))+             (:file "motion-designators" :depends-on ("package"))
              (:file "process-modules" :depends-on ("package"              (:file "process-modules" :depends-on ("package"
                                                    "control-turtlesim"                                                    "control-turtlesim"
                                                    "simple-plans"                                                    "simple-plans"
-                                                   "action-designators"))))))+                                                   "motion-designators"))))))
 </code> </code>
  
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 </code> </code>
  
-First, we use the ''cram-process-modules:def-process-module'' macro to define ''turtlesim-navigation'' as a process module taking one parameter (''motion-designator''). The process module then chooses which action to perform depending on the command specified in the designator: ''destructuring-bind'' maps the results from ''(reference motion-designator)'' to the variables ''command'' and ''motion'' respectively. Note that the inference rules we defined previously provide a name for the kind of motion we have (currently, all are ''drive''), and a ''turtle-motion'' object. We run an ''ecase'' on the kind of goal (currently, we only have the drive case) and use ''send-vel-cmd'' to tell the lower level to move the turtle around, given these parameters we infer from designator resolution.+First, we use the ''cram-process-modules:def-process-module'' macro to define ''turtlesim-navigation'' as a process module taking one parameter (''motion-designator''). The process module then chooses which motion to perform depending on the command specified in the designator: ''destructuring-bind'' maps the results from ''(reference motion-designator)'' to the variables ''command'' and ''motion'' respectively. Note that the inference rules we defined previously provide a name for the kind of motion we have (currently, all are ''drive''), and a ''turtle-motion'' object. We run an ''ecase'' on the kind of goal (currently, we only have the drive case) and use ''send-vel-cmd'' to tell the lower level to move the turtle around, given these parameters we infer from designator resolution.
  
 Let's try this out. Make sure you have ''roscore'' and ''turtlesim_node'' running. In a terminal tab for each, Let's try this out. Make sure you have ''roscore'' and ''turtlesim_node'' running. In a terminal tab for each,
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 <code lisp> <code lisp>
 TUT> (drive 5 2) TUT> (drive 5 2)
-[(TURTLE-PROCESS-MODULES) INFO] 1499958119.336: TurtleSim navigation invoked with motion designator `#<MOTION-DESIGNATOR ((TYPE+[(TURTLE-PROCESS-MODULES) INFO] 1562698751.679: TurtleSim navigation invoked with motion designator `#<A MOTION 
 +    (TYPE DRIVING) 
 +    (SPEED 5) 
 +    (ANGLE 2)>'
 +
 +</code> 
 + 
 +You should also see the turtle move in the TurtleSim window and trace the required trajectory. 
 + 
 + 
 +==== Adding more process modules for the TurtleSim ==== 
 + 
 +When adding new motions for a robot, we can either add them to a existing process module or write a new one. A process module only ever executes one designator at a time. This is to prevent unwanted behaviour when executing multiple designators in parallel or quick succession. But when a process module is called while still executing, the incoming call will be queued and executed as soon as the current execution is finished. 
 +For example, if we wanted the robot to grasp something and then stack it onto something else. If these motions were executed in parallel the arm would do neither because the commands would interfere with each other. Through the use of process modules, we don't have to worry about this. 
 +So to make this decision, we need to think about resources on the robot (eg. arms or the base of the robot). 
 + 
 +Our ''turtlesim-navigation'' is for the (abstract) resource 'driving' of the turtle. We now want to add the motions for moving and for setting the pen. Former uses the same resource as the navigation process module, so we should add it to the existing process module. The latter however doesn't, so we should add it as a new process module. 
 + 
 +To add the move motion to the existing process module, we add a new case to the ''ecase''. It should look like this: 
 + 
 +<code lisp> 
 +(def-process-module turtlesim-navigation (motion-designator) 
 +  (roslisp:ros-info (turtle-process-modules) 
 +                    "TurtleSim navigation invoked with motion designator `~a'." 
 +                    motion-designator) 
 +  (destructuring-bind (command motion) (reference motion-designator) 
 +    (ecase command 
 +      (drive 
 +         (send-vel-cmd 
 +          (turtle-motion-speed motion) 
 +          (turtle-motion-angle motion))) 
 +      (move 
 +       (move-to motion))))) 
 +</code> 
 + 
 +Since ''move-to'' takes a 3d-vector as a parameter we only have to pass ''motion'' to it. 
 + 
 + 
 +To add the new process module, append this to your ''process-modules.lisp'' file. 
 + 
 +<code lisp> 
 +(def-process-module turtlesim-pen-control (motion-designator) 
 +  (roslisp:ros-info (turtle-process-modules) 
 +                    "TurtleSim pen control invoked with motion designator `~a'." 
 +                    motion-designator) 
 +  (destructuring-bind (command motion) (reference motion-designator) 
 +    (ecase command 
 +      (set-pen 
 +       (call-set-pen 
 +        (pen-motion-r motion) 
 +        (pen-motion-g motion) 
 +        (pen-motion-b motion) 
 +        (pen-motion-width motion) 
 +        (pen-motion-off motion)))))) 
 +</code> 
 + 
 +The code should look very familiar, because it's pretty close to our other process modul 
 + 
 + 
 +==== Executing process modules in parallel ==== 
 + 
 +To demonstrate how process modules work when called in parallel, we will call the same process module twice. You can execute the following in the REPL: 
 + 
 +<code lisp> 
 +TUT> (top-level 
 +    (with-process-modules-running (turtlesim-navigation turtlesim-pen-control) 
 +      (let ((goal (desig:a motion (type moving) (goal (9 1 0)))) 
 +            (trajectory (desig:a motion (type driving) (speed 3) (angle 8)))) 
 +        (cpl:par 
 +          (pm-execute 'turtlesim-navigation goal) 
 +          (pm-execute 'turtlesim-navigation trajectory))))) 
 +[(TURTLE-PROCESS-MODULES) INFO] 1500997686.711: TurtleSim navigation invoked with motion designator `#<MOTION-DESIGNATOR ((TYPE 
 +                                                                           MOVING) 
 +                                                                          (GOAL 
 +                                                                           (9 1 
 +                                                                            0))) {1006DBC893}>'
 +WARNING: 
 +   Process module #<TURTLESIM-NAVIGATION 
 +                    {10074C0293}> already processing input. Waiting for it to become free. 
 +[(TURTLE-PROCESS-MODULES) INFO] 1500997690.065: TurtleSim navigation invoked with motion designator `#<MOTION-DESIGNATOR ((TYPE
                                                                            DRIVING)                                                                            DRIVING)
                                                                           (SPEED                                                                           (SPEED
-                                                                           5)+                                                                           3)
                                                                           (ANGLE                                                                           (ANGLE
-                                                                           2)) {1006979703}>'+                                                                           8)) {1006DBCC73}>'
-1+T
 </code> </code>
  
-You should also see the turtle move in the TurtleSim window and trace the required trajectory.+Here we use the ''par'' macro to call the same process module twice in parallel. When looking at the turtle we see, that it first moves to the bottom-right corner and then drives in a circle for a second. So the two designators were not executed in parallel because they were executed with the same process module. Also a warning gets printed stating, that the program waits for the process module to be free before executing the next designator.
  
-== Next ==+If we use two different process modules, they can in fact be called in parallel:
  
-Let's have look at location designators and other ways to move the turtle, as well as have some more practice with designator resolution and process modules ...+<code lisp> 
 +TUT> (top-level 
 +    (with-process-modules-running (turtlesim-navigation turtlesim-pen-control) 
 +      (let ((goal (desig:a motion (type moving) (goal (9 9 0))))) 
 +        (cpl:par 
 +          (pm-execute 'turtlesim-navigation goal) 
 +          (dotimes (i 10) 
 +            (pm-execute 'turtlesim-pen-control 
 +                      (let ((?r (random 255)) 
 +                            (?g (random 255)) 
 +                            (?b (random 255)) 
 +                            (?width (+ 3 (random 5)))) 
 +                      (desig:motion (type setting-pen) (r ?r) (g ?g) (b ?b) (width ?width)))) 
 +            (sleep 0.5)))))) 
 +[(TURTLE-PROCESS-MODULES) INFO] 1500997786.329: TurtleSim navigation invoked with motion designator `#<MOTION-DESIGNATOR ((TYPE 
 +                                                                           MOVING) 
 +                                                                          (GOAL 
 +                                                                           (9 9 
 +                                                                            0))) {1005164AC3}>'
 +[(TURTLE-PROCESS-MODULES) INFO] 1500997786.347: TurtleSim pen control invoked with motion designator `#<MOTION-DESIGNATOR ((TYPE 
 +                                                                            SETTING-PEN) 
 +                                                                           (R 
 +                                                                            220) 
 +                                                                           (G 
 +                                                                            115) 
 +                                                                           (B 
 +                                                                            14) 
 +                                                                           (WIDTH 
 +                                                                            7)) {10072183E3}>'
 +                                                                             
 +[ ... ] 
 +                                                                             
 +[(TURTLE-PROCESS-MODULES) INFO] 1500997791.126: TurtleSim pen control invoked with motion designator `#<MOTION-DESIGNATOR ((TYPE 
 +                                                                            SETTING-PEN) 
 +                                                                           (R 
 +                                                                            225) 
 +                                                                           (G 
 +                                                                            228) 
 +                                                                           (B 
 +                                                                            156) 
 +                                                                           (WIDTH 
 +                                                                            3)) {1002B903C3}>'
 +
 +</code> 
 + 
 +Here we call the navigation process module to move the turtle to the upper right corner and our other process module to change the pen color and width twice every second. When looking at the turtle we can see it moving to the upper right corner while randomly changing its pen. 
 + 
 +As stated above this behaviour is to ensure that a single resource on a robot isn't used by multiple functions at oncewhile not hindering the parallel execution of independent resources. But keep in mind, that this is only true for the low-level motions. If a robots arms should grasp something and its base is moved, the grasping might fail, although these motions are not necessarily controlled by the same process module. 
 + 
 + 
 +== Next == 
 +So far we called process modules directlySometimes it's better to let the system decide on its own … 
  
-[[tutorials:beginner:location_designators|Using location designators with the turtlesim]]+[[tutorials:beginner:assigning_actions_2|Automatically choosing a process module for a motion]]