| Note: This tutorial assumes that you have completed the previous tutorials: Tivaware and toolchain setup. |
 Please ask about problems and questions regarding this tutorial on answers.ros.org. Don't forget to include in your question the link to this page, the versions of your OS & ROS, and also add appropriate tags. |
RGB service
Description: EK-TM4C123GXL board over CDC USB device provides a custom message service for changing LED color.Tutorial Level: INTERMEDIATE
Contents
Introduction
The last tutorial of this series will show you how to create a custom service message and service server over rosserial.
The code relative to this tutorial can be found in the directory rgb_srv.
ColoRGBA service message
Let's analyze the message file found in srv/ColorRGBA.srv.
std_msgs/ColorRGBA color --- bool result
As a request we have a color field, of type std_msgs/ColorRGBA and as response we get a bool result.
package.xml & CMakeLists.txt
On the package's package.xml and top level CMakeLists.txt we need dependencies and rules to generate the new service message.
package.xml
Dependencies on package.xml:
<build_depend>message_generation</build_depend> <run_depend>message_runtime</run_depend>
CMakeLists.xml
(...) find_package(catkin REQUIRED COMPONENTS message_generation rosserial_client rosserial_tivac std_msgs ) add_service_files( FILES ColorRGBA.srv ) generate_messages( DEPENDENCIES std_msgs ) catkin_package( CATKIN_DEPENDS message_runtime std_msgs ) (...)
The required dependencies and instructions to generate the service message files.
Code
Similarly to the subscriber tutorial, we need to register a service server and assign to it a callback to handle the incoming requests and produce responses.
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 <rgb.h>
9 }
10 // ROS includes
11 #include <ros.h>
12 // Our custom service message
13 #include "rosserial_tivac_tutorials/ColorRGBA.h"
14
15 uint32_t current_color[3] = {0xFFFE, 0xFFFE, 0xFFFE};
16 float current_intensity = 1.f;
17 void color_cb(const rosserial_tivac_tutorials::ColorRGBARequest& req,
18 rosserial_tivac_tutorials::ColorRGBAResponse& resp)
19 {
20 current_color[0] = req.color.r * 0xFFFE;
21 current_color[1] = req.color.g * 0xFFFE;
22 current_color[2] = req.color.b * 0xFFFE;
23 current_intensity = req.color.a;
24 RGBSet(current_color, current_intensity);
25
26 resp.result = true;
27 }
28
29 // ROS nodehandle and subscriber
30 ros::NodeHandle nh;
31 ros::ServiceServer<rosserial_tivac_tutorials::ColorRGBARequest,
32 rosserial_tivac_tutorials::ColorRGBAResponse> rgb_service("led", &color_cb);
33
34 int main(void)
35 {
36 // TivaC application specific code
37 MAP_FPUEnable();
38 MAP_FPULazyStackingEnable();
39 // TivaC system clock configuration. Set to 80MHz.
40 MAP_SysCtlClockSet(SYSCTL_SYSDIV_2_5 | SYSCTL_USE_PLL | SYSCTL_XTAL_16MHZ | SYSCTL_OSC_MAIN);
41
42 // Setup RGB driver
43 RGBInit(0);
44 RGBSet(current_color, current_intensity);
45
46 // ROS nodehandle initialization and topic registration
47 nh.initNode();
48 nh.advertiseService<rosserial_tivac_tutorials::ColorRGBARequest,
49 rosserial_tivac_tutorials::ColorRGBAResponse>(rgb_service);
50 bool nh_prev_state = false;
51
52 while (1)
53 {
54 // If subscribed, enable RGB driver
55 if (nh.connected() && !nh_prev_state)
56 {
57 RGBEnable();
58 nh_prev_state = true;
59 }
60 if (!nh.connected() && nh_prev_state)
61 {
62 RGBDisable();
63 nh_prev_state = false;
64 }
65
66 // Handle all communications and callbacks.
67 nh.spinOnce();
68
69 // Delay for a bit.
70 nh.getHardware()->delay(1000);
71 }
72 }
The relevant parts for this tutorial are herein explained.
Node handle instantiation and service server definition. The service is available over the service topic /led, of type rosserial_tivac_tutorials::ColorRGBA, handled by the color_cb callback.
After initializing the node, register the service server to the callback queue.
17 void color_cb(const rosserial_tivac_tutorials::ColorRGBARequest& req,
18 rosserial_tivac_tutorials::ColorRGBAResponse& resp)
19 {
20 current_color[0] = req.color.r * 0xFFFE;
21 current_color[1] = req.color.g * 0xFFFE;
22 current_color[2] = req.color.b * 0xFFFE;
23 current_intensity = req.color.a;
24 RGBSet(current_color, current_intensity);
25
26 resp.result = true;
27 }
The service callback receives the request, converting the values from the message to the LED driver. It then always returns a true result.
Build, flash and test
catkin_make catkin_make rosserial_tivac_tutorials_rgb_led_flash
Don't forget to connect the device USB port to your computer!
Run roscore and run serial_node.py from rosserial_python on the correct port /dev/ttyACM#.
roscore
When you successfully connect using `serial_node the LED will light up.
rosrun rosserial_python serial_node.py _port:=/dev/ttyACM0
On a new terminal window, call the service with a new color.
rosservice call /led std_msgs/ColorRGBA "r: 0.0 g: 0.0 b: 1.0 a: 1.0"
It should change to the brightest blue.
