Creating controllers

To program the MCU Robot, a custom controller needs to be created and compiled, and then, the robot needs to point to the newly created controller executable.

To create a your robot controller, use the WeBots menu: Wizards -> New Robot Controller. Use C as the controller language. Name the controller, however you want. In this example, the name will be my_controller.

WeBots creates a new folder within the controllers folder of the project and two files:

• my_controller.c: The source code for the controller, to be modified.
• Makefile: The instructions for compiling the controller, to be edited once.

Modify the Makefile

Find the Makefile in the my_controller folder and modify the section before the "do not mofify" tag to include C_SOURCES and INCLUDE path definition. Make sure that you rename my_controller.c to the name you chose for your controller.

###-----------------------------------------------------------------------------

C_SOURCES = my_controller.c ../../libraries/renesas/renesas_api.c ../../libraries/renesas/renesas_api_webots.c
INCLUDE = -I"include" -I"../../libraries/renesas/include"

### Do not modify: this includes Webots global Makefile.include
null :=
space := $(null) $(null)
WEBOTS_HOME_PATH=$(subst $(space),\ ,$(strip $(subst \,/,$(WEBOTS_HOME))))
include $(WEBOTS_HOME_PATH)/resources/Makefile.include

Default program

To start programming the MCU car, replace the code in my_controller.c with the following.

#include "renesas_api.h"

int main(int argc, char **argv)
{
  wb_robot_init();
  init();
  while (wb_robot_step(TIME_STEP) != -1)
  {
    update();
  };
  wb_robot_cleanup();
  return 0;
}

Before compiling and running the program, let us examine the function call of the default program.

#include "renesas_api.h": The Renesas MCU Rally application programming interface (API) is included. The API defines the functions that you can call to control your sensors and actuators.

wb_robot_init();: The main program initializes the WeBots API (required by WeBots).

init();: Initializes the Renesas API.

update();: Updates the sensor data of the robot (line sensors, encoders). Needs to be called every simulation time step.

wb_robot_cleanup();: Frees the resources (required by WeBots).

Notice that the update function runs repeatedly inside a while loop. The code in the while loop is executed every controller step which is defined to be 5 ms and is the same as the simulation step. The majority of your code will need to be executed repeatedly and will therefore need to be placed after the update function inside the while loop.

Compiling and running

Before writing a controller that actually moves the robot, try to compile the controller and link it to the robot.

• With my_controller.c opened in the WeBots code editor, click the gear icon to compile.
• Modify the controller field in the MCUCar asset to point to my_controller.
• Expand the MCUCar asset in the scene tree view (left side of WeBots).
• Click on the controller field, Select..., my_controller.

The robot should now stay in place once the simulation is run.