Getting Familiar with Programming in WindRiver

This is my second topic on the WindRiver IDE platform. Hopefully though, this topic will be able to be more broad on understanding the specifics of code.

Anyway… I’ve been trying to understand the sample code and trying to make sense of the Sample Code for a few days now (I’ve finally installed WindRiver) and I still can’t get the gist of it. There’s a number of issues surrounding this problem, most of it having to do with getting used to OOP but more importantly, learning what all the new function names, keywords and operators do (for example: what the heck is ‘->’?).

If someone can upload the sample code (if not I’ll do it a bit later…) and kinda explain some of the things in the code (like what certain functions do and what certain keywords mean), I think it’ll immensely help not only me, but other people trying to understand what’s in the sample code.

Thanks,

  • Daniel

Here’s the sample source code…

#include "WPILib.h"

/**
 * This is a demo program showing the use of the RobotBase class.
 * The SimpleRobot class is the base of a robot application that will automatically call your
 * Autonomous and OperatorControl methods at the right time as controlled by the switches on
 * the driver station or the field controls.
 */
class RobotDemo : public SimpleRobot
{
	RobotDrive *myRobot; // robot drive system
	Joystick *stick; // only joystick
	DriverStation *ds; // driver station

public:
	RobotDemo(void)
	{
		ds = DriverStation::GetInstance();
		myRobot = new RobotDrive(1, 2); // create robot drive base
		stick = new Joystick(1); // create the joysticks
		GetWatchdog().SetExpiration(100);
	}

	/**
	 * Drive left & right motors for 2 seconds then stop
	 */
	void Autonomous(void)
	{
		GetWatchdog().SetEnabled(false);
		myRobot->Drive(0.5, 0.0); 	// drive forwards half speed
		Wait(2000); 				//    for 2 seconds
		myRobot->Drive(0.0, 0.0); 	// stop robot
	}

	/**
	 * Runs the motors with arcade steering. 
	 */
	void OperatorControl(void)
	{
		GetWatchdog().SetEnabled(true);
		while (IsOperatorControl())
		{
			GetWatchdog().Feed();
			myRobot->ArcadeDrive(stick); // drive with arcade style (use right stick)
		}
	}
};

START_ROBOT_CLASS(RobotDemo);


I’m pretty sure you’ll know most of it already, but just in case for someone else who is trying to get used to c/c++ itself, i’ll explain from the very beginning

#include "WPILib.h"

/**
 * This is a demo program showing the use of the RobotBase class.
 * The SimpleRobot class is the base of a robot application that will automatically call your
 * Autonomous and OperatorControl methods at the right time as controlled by the switches on
 * the driver station or the field controls.
 */
class RobotDemo : public SimpleRobot
{
	RobotDrive *myRobot; // robot drive system
	Joystick *stick; // only joystick
	DriverStation *ds; // driver station

public:
	RobotDemo(void)
	{
		ds = DriverStation::GetInstance();
		myRobot = new RobotDrive(1, 2); // create robot drive base
		stick = new Joystick(1); // create the joysticks
		GetWatchdog().SetExpiration(100);
	}

	/**
	 * Drive left & right motors for 2 seconds then stop
	 */
	void Autonomous(void)
	{
		GetWatchdog().SetEnabled(false);
		myRobot->Drive(0.5, 0.0); 	// drive forwards half speed
		Wait(2000); 				//    for 2 seconds
		myRobot->Drive(0.0, 0.0); 	// stop robot
	}

	/**
	 * Runs the motors with arcade steering. 
	 */
	void OperatorControl(void)
	{
		GetWatchdog().SetEnabled(true);
		while (IsOperatorControl())
		{
			GetWatchdog().Feed();
			myRobot->ArcadeDrive(stick); // drive with arcade style (use right stick)
		}
	}
};

START_ROBOT_CLASS(RobotDemo);

#include “WPILib.h” <— You’re including header file called “WPILib.h” to your source to use various variables, functions, etc

class RobotDemo : public SimpleRobot <—You’re declaring(and defining below) the class called “RobotDemo” which is derived from class called “SimpleRobot”, and you’ll access to public members of “SimpleRobot” class.
{ <— you’re now defining the class
RobotDrive *myRobot; <—you’re declaring RobotDrive type pointer variable called “myRobot”
Joystick *stick; <— you’re declaring Joystick type pointer variable called “stick”
DriverStation *ds; <— you’re declaring DriverStation type pointer variable called “ds”

public: <—you’re adding public members
RobotDemo(void) <—you’re declaring and defining constructor
{ <— you’re now defining the constructor
ds = DriverStation::GetInstance(); <— variable “ds” equals whatever value “GetInstance()” function under class called “DriverStation” returns
myRobot = new RobotDrive(1, 2); <— you’ll assign memory for pointer variable called “myRobot”, and the size of that memory will be “RobotDrive(1,2)”
stick = new Joystick(1); <— you’ll assign memory for pointer variable called “stick”, and the size of that memory will be “Joystick(1)”
GetWatchdog().SetExpiration(100); <— you’ll set the watchdog timer expiration to 100ms
} <— you’re done defining the constructor

void Autonomous(void)  &lt;--- you're declaring void type function called "Autonomous" taking no parameters
{    &lt;--- you'll now define the function
	GetWatchdog().SetEnabled(false);   &lt;--- you'll disable the watchdog timer
	myRobot-&gt;Drive(0.5, 0.0); 	&lt;--- execute "Drive(0.5,0.0)" using arrow operator(-&gt;) to access its(myRobot pointer's) member function
	Wait(2000);   &lt;--- execute function called "Wait", taking one parameter, which value you put is 2000
	myRobot-&gt;Drive(0.0, 0.0); 	&lt;---- execute "Drive(0.0,0.0)" using arrow operator(-&gt;) to access its(myRobot pointer's) member function
}   &lt;--- you're done defining function


void OperatorControl(void)  &lt;--- you're declaring void type function called "OperatorControl" taking no parameters
{    &lt;--- you're defining the function
	GetWatchdog().SetEnabled(true);   &lt;--- you're setting watchdog timer
	while (IsOperatorControl())   &lt;---repeat while loop until "IsOperatorControl()" equals 0
	{     &lt;--- define while loop
		GetWatchdog().Feed();    &lt;--- feed the watchdog timer
		myRobot-&gt;ArcadeDrive(stick);  &lt;---execute "ArcadeDrive" function(and parameter it takes is stick variable) using arrow operator(-&gt;) to access its(myRobot pointer's) member function
	}     &lt;--- you're done defining while loop
}  &lt;--- you're done defining function

}; <— you’re done defining class

START_ROBOT_CLASS(RobotDemo); <— you’re calling function called “START_ROBOT_CLASS” with parameter “RobotDemo”

I was wondering if windriver has something similar to MS’s intellisense. I love using it in VS and was hoping to use it with WR

Eclipse, the platform Workbench is built on, has intellisense for C/C++ development. It isn’t nearly as good as Visual Studio in my opinion but still there.

this is a little off topic, but where/ what version of wind river should i download?

A version of WindRiver is included with the control system and it is tailored to FIRST and WPILib.

To koreabell:
Thanks for taking the time to actually go down the code step by step. I’ve been a bit busy over the holidays and I’ve only gotten to read what you wrote now.

To everyone:
One thing I noticed so far in the code, is the use of an “Arcade Joystick”. Is that referring to “tank-drive” type steering or to single joystick control of the robot? Also, is it possible to use a different type of steering mechanism, for example a steering wheel, to control the robot? If so, what other resources would I need and how will I be able to implement it in the source code?

Thanks for your time. I look forward to reading your replies.

  • Dan

If you read the WPI Robotics Library doxygen document (C Programming Reference),

under class “RobotDrive”, there’s definition for every function related to driving mechanism

Here’s description for “ArcadeDrive” function

if you want to make your robot to be controlled with tank drive system, there’s a function called “TankDrive”

Description for “TankDrive” function

there are more functions having same name -TankDrive- but taking different parameters so you should check it before you use it.

in the code you should call function by doing something like this


RobotDrive::TankDrive(Left,Right); //basic tank drive function under RobotDrive Class

or if you have RobotDrive type variable, you can do this also


variable->TankDrive(Left,Right);

and you can use steering wheel for controlling robot but, programming will be same since throttle stick or pedal will have/return y-axis value and the steering wheel will have/return x-axis value

Hey thanks again for the help. I really appreciate it.

I’m looking through the WPI C Programming Reference and things are slowly getting processed so that’s a good thing.

I think I have an idea on how I’ll implement control by steering wheel. But I have a more technical question ask you. I’ve noticed that the new Driver Station Unit has 4 USB ports available for use. It’s it okay to plug in any USB Human Interface Device into the DSU and program or do I have to configure it? Also, is there a way to directly obtain values from the joysticks for programming use?

Thanks again for everything.

When you’re initializing joystick, you have to put which port the joystick is plugged in to as parameter

on the sample code you’ll see this


stick = new Joystick(1); // create the joysticks

that “Joystick(1)” (which is constructor) means that it’ll have control over Joystick that is plugged into port 1 on Driver Station

if for some reason it doesn’t work, then it can be joystick driver software problem, which can be solved by copying driver file to USB Memory Stick(Mass Storage Device) and then plugging into driverstation.
I do not know the procedure of installing driver software since we didn’t get new controller yet, but I heard that it can be done on both on-line and off-line workshops

also as I searched through some beta testing teams’ codes, I found out that they were using Header & Source file for the joystick so I think it can be done via programming manually instead of installing device drivers. (I didn’t analyze that files so i might be wrong but it looked like those files are in charge of joysticks teams are using)

and to obtain values from joystick, if you read Joystick class under C programming reference, there are a lot of functions like GetX, GetY, GetZ, etc

you can use that to get values of joystick axis, buttons, and stuff like that

All this is very helpful information.

So, is this saying that there is a possibility of say, I plug in a random USB steering wheel into USB port 1 on the DSU, upload the driver files from a USB thumb drive (found off of the manufacturer’s website) and then program using the various functions and classes using the WindRiver IDE?

Hopefully someone releases some precompiled header files so that we have steering control instead of joysticks.

Yes, although you might not need to install device driver since steering wheel “joysticks” basically have same interface as that of normal joysticks(meaning that driverstation won’t actually notice the difference between normal joysticks and steering wheel joysticks)

last year we tried to make steering wheel to drive our robot, and i remember it returning x-axis value of 127 on idle position, 0 when turning wheel all the way to left, 255 when turning wheel all the way to right or vice versa (can’t remember exactly)

now, if you plug in mouse or something like that other than joystick-type HID, it’ll be a different story and I’m not even sure whether it’ll work or not, but as long as you plug in joystick-type HID, then you’ll do fine programming

That’s not exactly true. Right now, the only joysticks/steering wheels/etc. that the DS supports are standard HID joystick devices that don’t require drivers. There’s no (published, anyway) way to get any special drivers onto the DS. (see section 3.1.8 of the control system manual or look around the beta forums)

Also, keep in mind that the Driver’s Station is Linux based so if there were a way to use drivers, then they’d have to be for that platform.

maybe i got confused with upgrading firmware. sorry about that

Thanks both for the replies.

So in order to pull information from the HID joysticks, it has to be pure P&P that doesn’t require any drivers whatsoever? So, if we find such as device, everything else should be preconfigured? For example, for a steering wheel, the wheel provides x-values, and the pedals provide the y-values? Or is there anyway to preset specific functions to specific buttons or features of the joystick?

most of joysticks come with drivers when you buy, but that doesn’t mean you necessarily need that driver.

if you plug the joystick into the driver station, it’ll most likely recognize the device without driver(unless the joystick really need driver).

you’ll need WPILib to get information of joystick status, which can be interpreted as it is preconfigured.

you can assign specific functions to corresponding buttons by making if or switch case statements.

for example



	int button[13]; // find which button is pushed
	int a = 0; //how many buttons are pushed?
	
	for(int i = 0; i < 12; i++){  //Get what button(s) is/are pushed and save it in array variable
		if(Joystick::GetRawButton((i+1)) == TRUE){
			button[a] = i;
			a++;
		}
	}

	for(int i = 0; i < a; i++){
		switch(button*){
			case 0:  //if nothing is pushed
				break;
			case 1:  //if button1 is pushed
				DoThis();
				break;
			case 2:  //if button2 is pushed
				DoThat();
				break;
			case 3:  //if button3 is pushed
				DoThese();
				break;
			case 4:  //if button4 is pushed
				DoThose();
				break;
			case 5:  //if button5 is pushed
				DoIt();
				break;
			case 6:  //if button6 is pushed
				GoThere();
				break;
			case 7:  //if button7 is pushed
				ComeHere();
				break;
			case 8:  //if button 8 is pushed
				Shoot();
				break;
			case 9:  //if button 9 is pushed
				RunAway();
				break;
			case 10:  //if button 10 is pushed
				Stop();
				break;
			case 11:  //if button 11 is pushed
				DisableYourself();
				break;
			case 12:  //if button 12 is pushed
				AbortAndCatchOnFire();
				break;
		}
	}
	a = 0;
	for(int i = 0; i < 12; i++){  //reset
		button* = 0;
	}

i think you can have up to 12 buttons and i doubt you’ll assign all 12 buttons to its corresponding functions but that’s one way to do it.

the other way is having a lot(depends on how many buttons you’ll be assigning specific functions to) of if and else if statements

there might be other ways but I can’t think of it at the moment**

I see… Since there are 12 programmable buttons, I’m guessing that either the standard joystick is labeled or there’s a diagram showing what button corresponds to what… But what if we use a different joystick? Do we have to test which buttons match which input source?

most of the joysticks have number on each button, maybe except for trigger button and, if you’re using logitech joystick and cannot figure out which button is which, install logitech gaming software that came with the joystick(to computer), execute it with joystick plugged in to one of the computer’s usb ports, and start pressing buttons. the program will tell you what button you’re pressing.

i don’t know if other companies support those kind of software or not, but if you have logitech joystick, you can figure out that way

if you’re making your own usb joystick, then you’ll have to label it as you make it, but if you’re buying joystick, then i wouldn’t worry too much about not knowing which button is which

btw, if you want to test without robot or drivestation, run joystick-playable game and go to key configuration(or something like that), and try changing joystick key. it’ll show you which button you pushed after you assign a key (for most games)

Thanks for the reply. You’ve been really helpful ever since I posted this thread.

After much thinking (upon watching the game), I think we’ve made the decision to go with the USB joysticks that we’re given standard to our team (Logitech ATK3).

Right now though… I have another problem that has been giving me major problems. Aside from not being able to get our camera correctly connected and configured when it’s plugged into the cRIO… I’m not quite sure how I’m supposed to program it to track colors or shapes in WindRiver. Do I do so with pure code or is there another utility that helps monitor that? And of course… How am I supposed to implement that into the code.

Secondly… Right now, the only way I’ve gotten the motors to move is through the RobotBase class. Is there any other way to control a specific motor (whether it be Jaguars or Victors) a specific speed? The functions in WPIlib.h only tells you what speed you want to set it to… but there are no parameters that reference the PWM port the motor is plugged into…