08/2012Tanya Mishra1 EASYC for VEX Cortex Llano Estacado RoboRaiders FRC Team 1817.

08/2012 Tanya Mishra 1

EASYC for VEX CortexLlano Estacado RoboRaiders

FRC Team 1817


Humans and Machines Machines are built to perform useful tasks. The way a Machine works depends entirely on the way

the Human build it. Since Machines and Robots need a medium of

communication, a language called “Programming Language” is used.

EASYC, ROBOTC, C++, C all are programming languages.

The instructions in the language are called “Programs” and the human that writes the instructions is called the “Programmer”.


Task of Programmer: Understand Problem, Find a solution, Write a program to solve the problem in the required Programming language.

Task of Machine: Follow the program provided. A ROBOT is a Machine.


Planning and Behavior

Behavior: Action the Robot has to take. Big Behavior: Solving a maze Small Behavior: Turn Left, Move Forward, etc. Big Behavior is made up of Smaller Behaviors. Plan a Solution to the problem. Break down the plan into detailed smaller steps. Each step is a behavior the robot needs to follow. Sequence of these steps in English is called “pseudo-

code”.



“Flow charts” are a visual representation of the program flow.

Start and End: “Rounded Rectangles”. They contain the word “Start” or “End”, but can be more specific such as “Power Robot Off” or “Stop All Motors”.

Actions: “Rectangles”. They act as basic commands and process steps.

Decision blocks: “Diamonds”. These typically contain Yes/No questions. Based on the choice, the next step is determined.



Introduction to C Programming

EasyC is based on the the principles of C Programming.

We will cover the following concepts:

1. Basic Components of a C Program

2. Data Types and Variables

2. Conditional operators

3. Control Structures and Loops

4. Methods and Functions


A Basic C Program

#include<stdio.h> // Header File

void main(void) // Main function

{

// Body of the main function

}

Header file: Includes all the required words and instructions needed to write a program

Main function: Execution starts from here Body: stepwise Instructions to the Robot


Each Instruction to the robot is also called a “Statement”.

When the list of instruction is send to the VEX cortex, it read them from top to bottom and left to right.

Different Commands use different paired Punctuations such as “[]” “{}” “()”

“{..}” defines a body of one or more instructions. Also called a “Compound Statement”.

Every instruction in the body ends with a “;”. It shows the end of a instruction.


Comments are for the programmer to understand what a particular statement does.

Two kinds of comments:

1. // This is a one line comment

2. /* This is a more than one line

Comment.*/ C language is case sensitive: Upper and lower

cases are considered different.


Data types and Variables A “Variable” is a place to store a value. A variable has a “Type” and a “Name” “Type” deals with the type of Data the variable

will hold.

Type of Data:

Int: Whole Numbers. Positive, Negative, Zero

float(Floating Point): Decimal Point Numbers. Positive and Negative.

String: Text. Letters, Spaces and characters.


char(Characters): Single characters

bool(Boolean): True and False values

Declare a variable: int Age;

float Score;

string Name;

char Grade;

bool Pass;


Assign a variable: Age = 18;

Score = 90.5;

Name = “William”;

Grade = 'A';

Pass = True;

Declare and assign: int Age = 18;

float Score = 90.5;

string Name = “William”;

char Grade = 'A';

bool Pass = True;


Variable Naming Rules: A variable name can not have spaces in it. A variable name can not have symbols in it. A variable name can not start with a number. A variable name can not be the same as an

existing reserved word.

Scope of a Variable: Local variables: Within a certain block of code

or function. Cannot be accessed outside. Global variables: Can be accessed anywhere

in the code.


Using Variables in a print to screen function:

When printing a variable on the screen, the following syntax is used:

Print to screen function(“%type”,Variable);

Signed : + and - , unsigned: - , short: less range , long : more range


Conditional Operators Comparison operators

Relational Operator Example

> (Greater Than) 7 > 5

>= (Greater Than or Equal To) 7 >= 5 , 7 >= 7

< (Less Than) 5 < 7

<= (Less Than or Equal To) 5 < 7 , 7<=7

== (Equal To) 7 == 7

!= (Not Equal To) 7 != 5

= (Assignment Operator) number = 7


Logical operators:

Boolean Truth TableJoining two or more statements using “And” and “Or”

A: Its a Sunny Day

B: My Car is working

Can I go out?(A and B)

Can I go out?(A or B)

Yes Yes Yes Yes

Yes No No Yes

No Yes No Yes

No No No No


And : &&

Or : ||

Not : !

A B !A A && B A || B

True True False True True

True False False False True

False True True False True

False False True False False


Control Structures and LoopsControl Structure

IF statements:if(condition)

{

Instructions, if “condition” is True

}


IF-ELSE Statements:if(condition)

{

// Instructions, if “condition” is true

}

else

{

// Instructions, if “condition” is false

}


ELSE-IF Statements:if(condition1)

{

// Instructions, if “condition 1” is true

}

else if(condition 2)

{

// Instructions, if “condition 2” is true

}

else

{

// Instructions, if “condition 1” and “condition 2” are false

}


Switch Statements:switch(expression) //expression can only be an “int” or “char”

{

case Value-1:

// Instructions, if expression = Value-1

break;

case Value-2:

// Instructions, if expression = Value-2

break;

default:

// Instructions, if expression does not match any Value

}


Example:

char Grade = 'A';

switch(Grade)

{

case A:

Your Grade is A;

break;

case B:

Your Grade is B;

break;

default:

This is the default choice

}


Loops While loops:

while(condition)

{

// Instructions, if “condition” is true

}Note: Control Structures execute only once. On the other hand, while

loops execute continuously until the condition is false.

If the condition in the loop is always true, the loop never ends. Such a loop is called an “Infinite Loop”.

A loop will end only when the condition is false or there is a “break” statement.


Example:int count = 0; //Initialization

while(count <= 2) //Condition

{

PrintToScreen(“ I have %d apple \n”, count);

count = count + 1; //Increment

}

Output: I have 0 apple

I have 1 apple

I have 2 apple


For Loop:

for(initialization; condition; increment)

{

// Instructions, If “condition” is true

}

Similar to a while loop except that the initialization and increment are all together.

Note: Initialization is done only when the loop first starts. After that it is skipped.


Example:int count;

for(count =0; count <= 2; count = count +1)

{

PrintToScreen(“ I have %d apple \n”, count);

}

Output: I have 0 apple

I have 1 apple

I have 2 apple

Note: \n is called new lines. It prints the next sentence in a new line.


Methods and function

Functions are named sections of code that can be called from other sections of code.

Also called subroutines. Every executable statement in C must live in a

function. Functions have a Data type, name and input

values. Input values are called Parameters. They are

the values you want the function to work with.


The function definition specifies the “return value” and the “parameters” of the function:

<data type> FunctionName(<param1>, <param2>, ...)

{

<function body>

<return type>

}

Return type and Data type should be of the same kind.

Return type is “void” if nothing is to be returned.

Parameters is “void” if nothing is to be passed in.


Example:

int addition(int x, int y)

{

int z;

z = x+ y;

return z;

}

void main(void)

{

addition(2, 3);

}


Some Useful termsCompiler: Turns C program into the machine

language for the controller.

Loader: Loads the machine language output of the compiler (along with other stuff) into the robot controller.

Machine Language: What the robot controller actually understands. Found in .HEX files.

10110100

11100101

00001011


Download EASYC

Download Link: EASYC V2.0 for VEX

http://www.intelitekdownloads.com/easyCV4/


Updating EASYC

If the website says you need to update EasyC, you can do that by going to:

Help->Check for updates


Updating the Firmware on the Cortex Controller and Remote

Controller “Firmware” is a piece of sofware that access the

operating system on the processor and allows it to perform its task.

Step 1: Connect the Cortex/Remote Controller and your computer using the A-A USB cable. The LED should start flashing


Step 2: On your computer's taskbar, goto:

Start -> All Programs -> easyC v4 For Cortex -> IFI VEXNet Firmware Utility


Step 3: Select “SEARCH” if the response is (Upgrade required) then “BOOTLOAD” and YES


Step 4: Then click “DOWNLOAD”


Step 5: Afterward you should see the following:


Connecting the Cortex Controller and Remote Controller

Connect the two devices together and then turn

on the Remote Controller or micro controller. Wait until the VEXNet LED turns solid green.


EASYC First LookStep 1: File -> New Standalone Project->Joystick

Project(Wifi)



1. Function Block(Left): You can all the available functions and your project file information.

2. Main (Middle): Drag and Drop the functions here to see how they connect and get a visual look for the code. All You need to work with is the area between “Variables” and “End”.

3. Project Pane (Right) : See your project files and other files.

4. Build information (Bottom) : See any code building information here.


When running the Robot, the real time values in each port can be seen in the “Online Window”

Step 1: EASYC-> Build & Download -> Online Window


When running the Robot, any “print to screen” values can be seen in the “Terminal Window”

Step 1: EASYC-> Build & Download -> Terminal Window


You can open the controller configuration (Marked with a Red Arrow) and write down what you are going to plug in each port.


VEX Cortex Controller

The VEX Cortex Micro controller has the following ports:

8 Analog ports 12 Digital ports 6 Interrupt ports 8 Motor ports


VEX Remote Controller

Vex Remote control provides you with two joysticks (each having a x- axis and y-axis), eight buttons on the front and four additional buttons on the top.


Each set of buttons or a pair of joystick has an assigned channel number written next to it as shown in the figure. Each of these controls are accessed using the channel number they belong to.


Incorporating C Programming baics in EASYC

We start by placing the needed module between the “Variables” and “End” modules.

Creating a “While” loop:

Step 1: Click the “+” sign next to the Program Flow on your Function Panel (Left)

Step 2: Click and drag the “While loop” on to the Main panel (Middle) and place it between the two modules you need it to.


Step 3: In the “While loop” Window, enter the condition and click OK.

NOTE: For an infinite loop, we use condition = 1 .i.e. while(1), because 1 will always be 1 and so this condition will always be true.

Similarly, we can do for a if statement, else-if statements, switch statements and For Loops.


Creating Variables:

Step 1: Click on the “Variables” module in the Main panel.

Step 2: Enter the details of the Variable in the next Local variables Window and click OK.


Step 3: The variable is now stored in the “Variables” module. If you click on it again, you can see your variable.

Now, whenever trying to use the variable weather to set its value or get its value, it will appear in the drop down list of the inputs and outputs for the other control modules like sensors.


Creating User Functions: Creating a new Function:

Step 1: Project -> Add New Function

Step 2: Enter the Return type, name,

Arguments/Parameter list (if any)


Adding an existing Function:

Step 1: Project -> Add Existing Function

Step 2: Enter the Details and location

And a Search will be done.


Building and Downloading a Program

After writing your program, you need to build it and download it on to the robot.

Step 1: Connect your robot and your computer using the A-A USB Cable. Make sure your cortex is turned off right now as a safety precaution.

Step 2: Build and Download → Build and Download


Step 3: Click “Yes” on the Hex file build successful message window and your code will be downloaded.


Drives

Simple Tank Drive Tank Drive involves the use of both joysticks.

Step 1: Click the “+” next to the Joystick Module in the Left Pane and drop Tank- 2 Motor in the Middle Pane.


Step 2: Enter the Joystick Number(Joystick 1 is your primary remote Controller, Joystick 2 is used if you are using another remote controller to control your robot), the left and right joystick channels, the left and right motor port numbers and if you need to invert a motor, change the value to 1.


Simple Arcade Drive Arcade Drive uses one joystick to drive the

robot.

Step 1: Click the “+” next to the Joystick Module in the Left Pane and drop Arcade – 2 Motor in the Middle Pane.


Step 2: Enter the Joystick Number(Joystick 1 is your primary remote Controller, Joystick 2 is used if you are using another remote controller to control your robot), the joystick channel (Set the Rotate Channel to 1), the left and right motor port numbers and if you need to invert a motor, change the value to 1.


Motor Control

The buttons on you remote controller can be used to control motors on your robot.

Step 1: Click the “+” next to the Joystick Module and drag and drop the Joystick Digital to motor in the middle pane.


Step 2: Enter the joystick number, Channel number for the button group, the button number and the motor value -127(Backward) to 127(Forward). 0 makes the value stop. Finally, enter the motor port number.


Assigning Positive power Values(127) on both motors makes the robot go forward.

Lower speed of robot by assigning values less than full power(127).

Assigning negative power values(-127) on both motors makes the robot go reverse.

Assigning zero power values(0) on both motors makes the robot stay in place.

Turning of Motors


Point Turn: Turn in place (-63 and 63)

Swing Turn: Making one motor on and the other off makes the robot swing around the stationary wheels. (0 and 63)


Shaft Encoders/Rotation Sensor

Manual adjustments of power are not same for all robots and as the battery power drains, the robot is move shorter distances.

Shaft Encoders are used to control how far the Robot Moves.

Number of counts per Revolution on a axle mounted through the encoder center.

Max 360 up for forward movements and 360 down for reverse movements.


Encoders need to be set to zero before you use them. Clear the encoders for better consistency and precision on your robots movements.

Step 1: You can find the Quadrature encoder modules by clicking the “+” next to the inputs modules in the left panel.


The corresponding text functions for the Quadrature modules are as follows:

Start the Encoder:StartQuadEncoder(port number)

It is good practice to preset the value of encoder to 0 before use.

PresetQuadEncoder(port number, 0)

Get the number of ticks passed:ticks = GetQuadEncoder(port number)


Limit Switch Limit Switch is a Digital Sensor(0 and 1) When pressed, it provides a sensor value 1,

when released, it provides a sensor value 0.

Step 1: The limit switch module is in the Inputs modules in the left panel.

?? = GetDigitalInput(port number)


Potentiometers: A potentiometer is a Analog Sensor. It measures rotation between 0 to 250 (not 360

due to internal mechanical stops) degrees and return value ranging from 0 to approximately 4095.

?? = GetAnalogInput(port number)


Ultrasonic Range Finder Ultrasonic Range Finder allows us to sense

obstacles in the path of the robot and avoid bumping into them.


It measures distance to the obstacle using sound waves. It calculates the Distance depending on how long it takes for the sound wave to bounce back.

Distance = Speed * Time / 2

Step 1: Click the “+” next to the inputs and drag and drop the Ultrasonic sensor in the middle panel.


Step 2: Choose if you want to start or stop the sensor or get its value. Enter the interrupt port and the digital output port.


The corressponding text functions will be as follows:

StartUltrasonic(interrupt port numer, digital port number)

?? = GetUltrasonic((interrupt port numer, digital port number)


Timers

Timers are like “Stopwatches”. Used in competition to know how long the robot

has been working. You have access to 6 software Timers. The

time is in Microseconds (1 sec = 1000 ms)

Step 1: Click the “+” next to the Program Flow module and drag and drop the Timer module.


Step 2: Choose if you want to start, preset, get a value or stop the Timer. It is a good practice to Clear the Timer before use.


Wait

When Wait is used, the program execution is sidle for that period of time.

Step 1: Click the “+” next to the Program flow and Drag and drop the wait module. The wait module takes time in Microseconds.


Line Tracking Sensors

Below is shown a set of three Line tracking Sensors. Line tracking sensors work on the bases of Infrared Light. Each sensor has an Infrared LED and an Infrared Light sensor.


The LED emits light and the sensor detects the amount the light reflected back.

Light Surfaces = Low Sensor Reading Dark Surfaces = High Sensor Reading


The cortex gives a Sensor reading from 0 to 4095. The value does not correspond to any unit of measurement.

Thus it is important to take care of lighting conditions around the robot and the height at which the sensors are placed in order to determine the threshold of reading.


Using all three sensors allows us to detect the line as well as border of the line, corners and intersections, which is not possible if you use just one line tracking sensor.


Step 1: The Line tracking Module is present in the Input modules in the Left panel. Set the Analog Input and retrieve the value returned by the Line follower.


Create Competition Code

Step 1: File->New Competition Project->Timed Competition Project


The Autonomous Time and operator controlled time are in seconds. Each define the number of seconds the Autonomous code and the Operator control will run for.

Put down your autonomous and operator controlled code in the corresponding file modules. You can also change the running times for the autonomous and operator control mode by clicking on the modules.



That's all for EasyC for Cortex programming.

Thank you!

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08/2012Tanya Mishra1 EASYC for VEX Cortex Llano Estacado RoboRaiders FRC Team 1817.

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