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## note.0=[[rosserial_tivac/Tutorials/TivaWare Setup|Tivaware and toolchain setup]]
## descriptive title for the tutorial
## title = RGB subscriber
## multi-line description to be displayed in search
## description = EK-TM4C123GXL board over CDC USB device subscribes to ColorRGB msg type and change LED color.
## the next tutorial description (optional)
## next =
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## next.0.link= [[rosserial_tivac/Tutorials/RGB srv|RGB service]]
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<<IncludeCSTemplate(TutorialCSHeaderTemplate)>>

<<TableOfContents(4)>>

##startpage
== Introduction ==

Having created several publishers on the previous tutorials, its about time we implement a subscriber.

Our application will subscribe to the topic `/led` and change the color accordingly to the data on the ColorRGBA message.

== Source code explained ==

{{{
#!cplusplus block=srccode
#include <stdbool.h>
#include <stdint.h>
// TivaC specific includes
extern "C"
{
  #include <driverlib/sysctl.h>
  #include <driverlib/gpio.h>
  #include <rgb.h>
}
// ROS includes
#include <ros.h>
#include <std_msgs/ColorRGBA.h>

uint32_t current_color[3] = {0xFFFE, 0xFFFE, 0xFFFE};
float current_intensity = 1.f;
void color_cb(const std_msgs::ColorRGBA& msg)
{
  current_color[0] = msg.r * 0xFFFE;
  current_color[1] = msg.g * 0xFFFE;
  current_color[2] = msg.b * 0xFFFE;
  current_intensity = msg.a;
  RGBSet(current_color, current_intensity);
}

// ROS nodehandle and subscriber
ros::NodeHandle nh;
ros::Subscriber<std_msgs::ColorRGBA> rgb_sub("led", &color_cb);

int main(void)
{
  // TivaC application specific code
  MAP_FPUEnable();
  MAP_FPULazyStackingEnable();
  // TivaC system clock configuration. Set to 80MHz.
  MAP_SysCtlClockSet(SYSCTL_SYSDIV_2_5 | SYSCTL_USE_PLL | SYSCTL_XTAL_16MHZ | SYSCTL_OSC_MAIN);

  // Setup RGB driver
  RGBInit(0);
  RGBSet(current_color, current_intensity);

  // ROS nodehandle initialization and topic registration
  nh.initNode();
  nh.subscribe(rgb_sub);
  bool nh_prev_state = false;

  while (1)
  {
    // If subscribed, enable RGB driver
    if (nh.connected() && !nh_prev_state)
    {
      RGBEnable();
      nh_prev_state = true;
    }
    if (!nh.connected() && nh_prev_state)
    {
      RGBDisable();
      nh_prev_state = false;
    }

    // Handle all communications and callbacks.
    nh.spinOnce();

    // Delay for a bit.
    nh.getHardware()->delay(1000);
  }
}
}}}

Again, use the project `rgb_led` from `rosserial_tivac_tutorials package as reference to follow the tutorial.

<<CodeRef(srccode,42,43)>>
As always, the node is initiated and all the publishers and subscribers must be registered.


<<CodeRef(srccode,25,27)>>
Here we instantiate a new subscriber on the topic `/led` of message type `ColorRGBA`, handled by `color_cb` function.

<<CodeRef(srccode,14,23)>>
The callback function will be executed for each new received message.
It takes color and intensity values in the range [0 1] and applies the color to the board LED using the board specific library.

<<CodeRef(srccode,46,65)>>
Then execution is trapped inside a loop, continuously waiting for new messages on the topic.

However the LED will only be enabled when a valid node connection is present.

== Build and flash ==

By now you're an expert at this.
Build and flash the binary file into your board.

{{{
catkin_make
catkin_make rosserial_tivac_tutorials_rgb_led_flash
}}}

== Test it! ==
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, publish a new color.
{{{
rostopic pub /led std_msgs/ColorRGBA "r: 0.0
g: 1.0
b: 0.0
a: 1.0"
}}}

It should change to the brightest green.

##endpage
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## TutorialCategory
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