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Hello world publisher on TM4C123GXL

Introduction

This tutorial will take you step-by-step on how to set up your TivaC project on a catkin package using rosserial_client and rosserial_tivac.

All these tutorials are available on the repository.

Create your project

On your catkin workspace we'll create a new package.

catkin_create_pkg rosserial_tivac_tutorials rosserial_tivac rosserial_client std_msgs

Since you're completely familiar with ROS, you know this command will create a new package on your workspace with the name rosserial_tivac_tutorials. We're establishing a dependency on rosserial_tivac for the required libraries and rosserial_client for the client build macros. std_msgs is also required since we use these messages on our examples.

package.xml

Your package.xml should look like:

   1 <?xml version="1.0"?>
   2 <package>
   3   <name>rosserial_tivac_tutorials</name>
   4   <version>0.0.0</version>
   5   <description>The rosserial_tivac_tutorials package</description>
   6   <maintainer email="todo@todo.todo">todo</maintainer>
   7   <license>TODO</license>
   8 
   9   <buildtool_depend>catkin</buildtool_depend>
  10   
  11   <build_depend>rosserial_client</build_depend>
  12   <build_depend>rosserial_tivac</build_depend>  
  13   <build_depend>std_msgs</build_depend>
  14   
  15   <run_depend>rosserial_client</run_depend>
  16   <run_depend>rosserial_tivac</run_depend>
  17   <run_depend>std_msgs</run_depend>
  18 </package>

CMakeLists.txt

And your CMakeLists.txt file ought to contain the minimal dependency definitions by now.

   1 cmake_minimum_required(VERSION 2.8.3)
   2 project(rosserial_tivac_tutorials)
   3 
   4 find_package(catkin REQUIRED COMPONENTS
   5   message_generation
   6   rosserial_client
   7   rosserial_tivac
   8   std_msgs
   9 )

Write your code

Create a new directory 'chatter' and a new file inside called chatter.cpp with the following code:

   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 }
   9 // ROS includes
  10 #include <ros.h>
  11 #include <std_msgs/String.h>
  12 
  13 // ROS nodehandle
  14 ros::NodeHandle nh;
  15 
  16 std_msgs::String str_msg;
  17 ros::Publisher chatter("chatter", &str_msg);
  18 char hello[13] = "Hello world!";
  19 
  20 int main(void)
  21 {
  22   // TivaC application specific code
  23   MAP_FPUEnable();
  24   MAP_FPULazyStackingEnable();
  25   // TivaC system clock configuration. Set to 80MHz.
  26   MAP_SysCtlClockSet(SYSCTL_SYSDIV_2_5 | SYSCTL_USE_PLL | SYSCTL_XTAL_16MHZ | SYSCTL_OSC_MAIN);
  27 
  28   // ROS nodehandle initialization and topic registration
  29   nh.initNode();
  30   nh.advertise(chatter);
  31 
  32   while (1)
  33   {
  34     // Publish message to be transmitted.
  35     str_msg.data = hello;
  36     chatter.publish(&str_msg);
  37 
  38     // Handle all communications and callbacks.
  39     nh.spinOnce();
  40 
  41     // Delay for a bit.
  42     nh.getHardware()->delay(100);
  43   }
  44 }

Code explained

You should be familiar with developing C applications for these evaluation boards by now. Very little changes from your typical Tiva C application using Tivaware libraries.

   4 extern "C"
   5 {
   6   #include <driverlib/sysctl.h>
   7   #include <driverlib/gpio.h>
   8 }

But we are now compiling a C++ application with use Tivaware C libraries.

   9 // ROS includes
  10 #include <ros.h>
  11 #include <std_msgs/String.h>
  12 

Like a typical ROS application, we include the required headers.

  13 // ROS nodehandle
  14 ros::NodeHandle nh;
  15 
  16 std_msgs::String str_msg;
  17 ros::Publisher chatter("chatter", &str_msg);
  18 char hello[13] = "Hello world!";

We then declare:

1. Our one and only node handle.
2. The message to be published.

3. The publisher with topic name chatter.

4. The string we're publishing.

  23   MAP_FPUEnable();
  24   MAP_FPULazyStackingEnable();
  25   // TivaC system clock configuration. Set to 80MHz.
  26   MAP_SysCtlClockSet(SYSCTL_SYSDIV_2_5 | SYSCTL_USE_PLL | SYSCTL_XTAL_16MHZ | SYSCTL_OSC_MAIN);

These are MCU specific instructions to set up and configure the system.

  29   nh.initNode();
  30   nh.advertise(chatter);

Then the node is initialized, and any publisher, subscriber and service should be added to the callback queue.

  32   while (1)
  33   {
  34     // Publish message to be transmitted.
  35     str_msg.data = hello;
  36     chatter.publish(&str_msg);
  37 
  38     // Handle all communications and callbacks.
  39     nh.spinOnce();
  40 
  41     // Delay for a bit.
  42     nh.getHardware()->delay(100);
  43   }

Finally we trap the execution on a infinite loop, with the node publishing the string "Hello world!" when ros::spinOnce() is called, and all ROS communication callbacks are handled.

Revisiting CMakeLists.txt

Now it's time to include in our package's CMakeLists.txt file the rosserial_client macros to generate ROS libraries for our target and generate our catkin sub-project.

   1 cmake_minimum_required(VERSION 2.8.3)
   2 project(rosserial_tivac_tutorials)
   3 
   4 find_package(catkin REQUIRED COMPONENTS
   5   message_generation
   6   rosserial_client
   7   rosserial_tivac
   8   std_msgs
   9 )
  10 
  11 rosserial_generate_ros_lib(
  12   PACKAGE rosserial_tivac
  13   SCRIPT make_libraries_tiva
  14 )
  15 
  16 # Chatter tutorial
  17 rosserial_configure_client(
  18   DIRECTORY chatter
  19   TOOLCHAIN_FILE ${ROSSERIAL_TIVAC_TOOLCHAIN}
  20 )
  21 rosserial_add_client_target(chatter chatter.axf ALL)
  22 rosserial_add_client_target(chatter flash)
  23 rosserial_add_client_target(chatter size)
  24 rosserial_add_client_target(chatter dump)

  11 rosserial_generate_ros_lib(
  12   PACKAGE rosserial_tivac
  13   SCRIPT make_libraries_tiva

The rosserial_generate_ros_lib function creates a target called which will generate the rosserial client library, including messages headers. Called rosserial_tivac_tutorials_ros_lib.

  16 # Chatter tutorial
  17 rosserial_configure_client(
  18   DIRECTORY chatter
  19   TOOLCHAIN_FILE ${ROSSERIAL_TIVAC_TOOLCHAIN}

rosserial_configure_client will configure a new client subproject chatter with the specified toolchain file, provided by the package rosserial_tivac.

  20 )
  21 rosserial_add_client_target(chatter chatter.axf ALL)
  22 rosserial_add_client_target(chatter flash)
  23 rosserial_add_client_target(chatter size)

Each rosserial_add_client_target will create a specific target for the subproject chatter.

• rosserial_tivac_tutorials_chatter_chatter.axf: Build the project object file.

• rosserial_tivac_tutorials_chatter_flash: Creates the binary file and flashes it to the board.

• rosserial_tivac_tutorials_chatter_size: Prints the binary file size.

• rosserial_tivac_tutorials_chatter_dumps: Dumps the built object symbol table.

Subproject's CMakeLists.txt

Let's continue developing our application by adding the subproject's CMakeLists.txt.

Create a file chatter/CMakeLists.txt with the content:

   1 cmake_minimum_required(VERSION 2.8.3)
   2 project(chatter)
   3 
   4 # Include rosserial libraries for TivaC
   5 include_directories(${ROS_LIB_DIR})
   6 
   7 # Per project based definitions and options
   8 add_definitions(-DLED_HEARTBEAT)
   9 add_definitions(-DLED_COMM)
  10 add_definitions(-DROSSERIAL_BAUDRATE=57600)
  11 add_definitions(-DTX_BUFFER_SIZE=256)
  12 add_definitions(-DRX_BUFFER_SIZE=256)
  13 
  14 # Generate target for TivaC
  15 generate_tivac_firmware(
  16   SRCS chatter.cpp
  17   BOARD tm4c123gxl
  18 )

CMakeLists.txt explained

   2 project(chatter)

Defines the target's name.

   5 include_directories(${ROS_LIB_DIR})

Includes the generated ros_lib libraries, which are specific for TivaC.

   8 add_definitions(-DLED_HEARTBEAT)
   9 add_definitions(-DLED_COMM)

Optional defines. If you wish to claim the use of the heartbeat LED and communications LED, you can delete these defines.

  10 add_definitions(-DROSSERIAL_BAUDRATE=57600)

Baudrate definition when using communication through the UART over debug USB port. If undefined, 57600 is assumed.

  11 add_definitions(-DTX_BUFFER_SIZE=256)
  12 add_definitions(-DRX_BUFFER_SIZE=256)

Size of UART buffers.

  15 generate_tivac_firmware(
  16   SRCS chatter.cpp
  17   BOARD tm4c123gxl
  18 )

The generate_tivac_firmware function provided by rosserial_tivac package sets all the variables, libraries and build rules for our application.

You need to specify:

• SRCS: The source files to be compiled on your application.

• BOARD: tm4c123gxl or tm4c1294xl

Build & upload

Using catkin_make

Now we can build our application when we run catkin.

catkin_make rosserial_tivac_tutorials_chatter_chatter.axf

And also use the catkin target to flash the application.

catkin_make rosserial_tivac_tutorials_chatter_flash

Using catkin tools

Now we can build our application when we run catkin.

catkin build rosserial_tivac_tutorials

And also use the catkin target to flash the application.

catkin build --no-deps rosserial_tivac_tutorials --make-args rosserial_tivac_tutorials_chatter_flash

Test

Let's listen to our newly created topic from TivaC.

Run roscore.

roscore

Run serial_node.py from rosserial_python.

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

Watch the messages from the topic.

rostopic echo /chatter

Addendum

If there's a breakage you don't understand, a good first step is to clean your workspace (delete build and devel trees), and then re-run in verbose mode:

catkin_make VERBOSE=1