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Buttons publisher

Introduction

This particular tutorial follows the same general steps as the previous two.

However on this project we will use a custom message to publish the user button state on the EK-TM4C123GXL.

Another change from the previous projects, is the use of the device USB port. When connected to the computer, the board will enumerate as a CDC usb device.

For this tutorial you must get the reference files which can be found on rosserial_tivac_tutorials.

Custom message generation

Let's create a new file message on the new directory msgs/Buttons.msg.

std_msgs/Bool sw1
std_msgs/Bool sw2

package.xml & CMakeLists.txt

On the package's package.xml and top level CMakeLists.txt we will add new dependencies and rules to generate our new message.

package.xml

Add new dependencies on package.xml:

  <build_depend>message_generation</build_depend>  
  <run_depend>message_runtime</run_depend>

CMakeLists.xml

Add the new package message_generation dependency to find_package:

(...)
find_package(catkin REQUIRED COMPONENTS
  message_generation
  rosserial_client
  rosserial_tivac
  std_msgs
)
add_message_files(
  FILES Buttons.msg
)
generate_messages(
  DEPENDENCIES std_msgs
)
catkin_package(
  CATKIN_DEPENDS message_runtime std_msgs
)
(...)

As well as instructions to generate the new message files.

Also add the new subproject.

(...)
# Custom message - Button publisher
rosserial_configure_client(
  DIRECTORY buttons
  TOOLCHAIN_FILE ${ROSSERIAL_TIVAC_TOOLCHAIN}
)
rosserial_add_client_target(buttons buttons.axf ALL)
rosserial_add_client_target(buttons flash)
rosserial_add_client_target(buttons size)
(...)

Source code

Similarly to the previous tutorials, we'll create a publisher for the new Buttons message.

   1 #include <stdbool.h>
   2 #include <stdint.h>
   3 // TivaC specific includes
   4 extern "C"
   5 {
   6   #include <driverlib/sysctl.h>
   7   #include <driverlib/gpio.h>
   8   #include "buttons.h"
   9 }
  10 // ROS includes
  11 #include <ros.h>
  12 // Custom ROS message
  13 #include "rosserial_tivac_tutorials/Buttons.h"
  14 
  15 // ROS nodehandle
  16 ros::NodeHandle nh;
  17 
  18 rosserial_tivac_tutorials::Buttons button_msg;
  19 ros::Publisher button_publisher("button_state", &button_msg);
  20 
  21 int main(void)
  22 {
  23   // TivaC application specific code
  24   MAP_FPUEnable();
  25   MAP_FPULazyStackingEnable();
  26   // TivaC system clock configuration. Set to 80MHz.
  27   MAP_SysCtlClockSet(SYSCTL_SYSDIV_2_5 | SYSCTL_USE_PLL | SYSCTL_XTAL_16MHZ | SYSCTL_OSC_MAIN);
  28 
  29   uint8_t button_debounced_delta;
  30   uint8_t button_raw_state;
  31   ButtonsInit();
  32 
  33   // ROS nodehandle initialization and topic registration
  34   nh.initNode();
  35   nh.advertise(button_publisher);
  36 
  37   while (1)
  38   {
  39     uint8_t button_debounced_state = ButtonsPoll(&button_debounced_delta, &button_raw_state);
  40     // Publish message to be transmitted.
  41     button_msg.sw1.data = button_debounced_state & LEFT_BUTTON;
  42     button_msg.sw2.data = button_debounced_state & RIGHT_BUTTON;
  43     button_publisher.publish(&button_msg);
  44 
  45     // Handle all communications and callbacks.
  46     nh.spinOnce();
  47 
  48     // Delay for a bit.
  49     nh.getHardware()->delay(100);
  50   }
  51 }

Very few changes comparing to the "hello world" publisher.

  13 #include "rosserial_tivac_tutorials/Buttons.h"
  14 

  18 rosserial_tivac_tutorials::Buttons button_msg;
  19 ros::Publisher button_publisher("button_state", &button_msg);

We now include the header files corresponding to the Buttons message, and also instantiate the message and publisher for the topic with name /button_state.

  29   uint8_t button_debounced_delta;
  30   uint8_t button_raw_state;
  31   ButtonsInit();

MCU specific code to set up the buttons' pins.

  37   while (1)
  38   {
  39     uint8_t button_debounced_state = ButtonsPoll(&button_debounced_delta, &button_raw_state);
  40     // Publish message to be transmitted.
  41     button_msg.sw1.data = button_debounced_state & LEFT_BUTTON;
  42     button_msg.sw2.data = button_debounced_state & RIGHT_BUTTON;
  43     button_publisher.publish(&button_msg);
  44 
  45     // Handle all communications and callbacks.
  46     nh.spinOnce();
  47 
  48     // Delay for a bit.
  49     nh.getHardware()->delay(100);
  50   }

On the main loop, we read the button state using the function ButtonsPoll, and with the result we fill up the message before publishing.

The message is then queued when .publish is executed and transmitted when .spinOnce() is called.

Build & flash

catkin_make rosserial_tivac_tutorials_buttons_buttons.axf
catkin_make rosserial_tivac_tutorials_buttons_flash

Test it up

Hold on! Don't forget to connect the device USB port to your computer!

You should be able to see the device under the name /dev/ttyACM#, depending on how many devices you have connected.

Run roscore and run serial_node.py from rosserial_python on the correct port /dev/ttyACM#.

roscore

rosrun rosserial_python serial_node.py _port:=/dev/ttyACM0

rostopic echo /button_state

Press any of the two buttons, and watch the output of the topic change.