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RobotC – A Tutorial II

RobotC – A Tutorial II . Learning from yesterday. The IDE Functions and usage of various panels Top Menubar Side Functions panel Code Window Error Window Compiling/Downloading the code Running the program C Programming Syntax Capitalization Whitespaces Comments Variables

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RobotC – A Tutorial II

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  1. RobotC – A Tutorial II

  2. Learning from yesterday • The IDE • Functions and usage of various panels • Top Menubar • Side Functions panel • Code Window • Error Window • Compiling/Downloading the code • Running the program • C Programming Syntax • Capitalization • Whitespaces • Comments • Variables • Boolean Algebra REVISION

  3. Learning from yesterday • Control Structures • Tasks • Functions • If-Else/Switch • While/For Today we are going to look at specific commands and options available in RobotC for controlling the NXT REVISION

  4. Section Overview • Reserved Words Motors Timers LCD Display • Sensor Configuration • Debugger Usage Tasks Functions If-Else/Switch While/For SECTION 3

  5. Overview • RobotC has a variety of commands, interfaces and options which deal specifically with robots. Some of these are • Reserved words like motor, timers (keywords) • Sensor interfaces • Live debugger ROBOTC FEATURES

  6. Keywords • RobotC has a variety of keywords which are used for issuing specific commands to the NXT controller • As it is not possible to cover all the commands in detail here, only the main ones will be discussed. • Explore the rest of the options by using the help available within the programming environment or online version (as explained earlier) ROBOTC FEATURES

  7. Motors Motor control – Turn on/off at a certain power level General Syntax motor[output] = power; Parameters Output – Determine the motor to affect. This can be motorA, motorB, motorC This command just gives power to the 3 output ports A, B, C in a certain fashion. This can also be fed to a circuit to control other devices Power – Determines the power at which the motor is to be run. This can take any integer value from -100 (full reverse) to 100 (full forward) Examples motor[motorA] = 60; //Run motor A at 60% power motor[motorB] = -50; //Run motor B in reverse at 50% motor[motorC] = 100; //Run motor C at full power forward ROBOTC FEATURES

  8. Motors – 5 minute activity Using the simple motor command, try to write a program that spins the RoboCar as fast as possible How fast does it rotate? (RPM) ROBOTC FEATURES

  9. Motors – 5 minute activity How did you do? Here is one solution: task main() { motor[motorA] = 100; motor[motorB] = -100; while(true); } …where you turn both motors at full power, opposite direction. At this point, just take a moment to think of all the other factors which may have affected your spin rate (battery power, weight imbalance, friction, etc) Robust code accounts for as many uncertainties as possible ROBOTC FEATURES

  10. Timers – Wait Timers The wait commands allow you to insert delays into your program. Its like starting a stop watch and pause the execution of your program. The pause in execution means that the next command will not be executed till after the timer expires. However, the actions due to the commands already issued will continue. There are two commands related to this wait1Msec(wait_time); wait10Msec(wait_time); Parameters wait_time – Refers to the time for which the program pauses before proceeding to the next step. The units are either milliseconds (1/1000 of sec) or 10s of milliseconds (1/100 of sec) ROBOTC FEATURES

  11. Timers – Examples The following examples uses the wait function to allow the motors to operate for 1 second at a time. ROBOTC FEATURES

  12. Motors – 5 minute activity Using the wait command, try to write a program that rolls the car forward a distance of approximately 2 feet ROBOTC FEATURES

  13. Motors – 5 minute activity How did you do? Does your code look something like this? task main() { motor[motorA] = 100; motor[motorB] = -100; wait1Msec(2000); // however long it takes to go 2ft } ROBOTC FEATURES

  14. LCD Display • The LCD display on the NXT is a 6 line display that can be controlled via functions in RobotC. • It can support a display of 16 characters per line • The display is an extremely useful resource during the debugging phase, for observing the values of various inputs and outputs. • If left unmodified, the LCD will display the readings of the input sensors and the output power level of the motors. ROBOTC FEATURES

  15. LCD Display - Functions Two functions that may be useful to access the LCD are nxtDisplayStringAt(xPos,yPos,text,var1,var2,var3) – print text eraseDisplay()– clear the NXT display Parameters xPos - Number of pixels away from the left of the display that you want your string to be printed at. yPos - This integer value is the number of pixels away from the bottom of the display that you want your string to be printed at. text - The text parameter is what shows up on the screen. This will be a string enclosed in quotes up to 16 characters. You may also display up to 3 variables in this string by adding %d, %f (conversion specifications) up to three times. var1, var2, var3 - These (optional) parameters define which variables will be displayed to the screen and each must correspond to a separate %d, %f within the text parameter. ROBOTC FEATURES

  16. Motors - Encoder Each standard Lego motor has an inbuilt encoder that can be used to measure the amount the motor has turned by, or turn the motor by a specific number of degrees General Syntax (to obtain the reading) myVar =nMotorEncoder[output] General Syntax (set the turning amount) nMotorEncoderTarget[output] = numCounts Parameters output – Determine the motor to affect. numCounts – The number of encoder counts that the motor must turn before stopping myVar – a variable that gets assigned the current value of the encoder ROBOTC FEATURES

  17. Motors - Encoder Encoder Example (To turn to desired value by setting) // Set degrees that motor A must turn to 1000 nMotorEncoderTarget[motorA] = 1000; // Turn on Motor A. It will automatically stop // after turning for the desired amount motor[motorA] = 75; ROBOTC FEATURES Encoder Example (To turn to desired value by observation) // Turn on motorA until it has turned 1000 degrees motor[motorA] = 75; while(nMotorEncoder[motorA] <= 1000) ; // do nothing motor[motorA] = 0; // requires explicit stop

  18. Motors – 10 minute activity Write a creative programming solution to navigate the following course – without using any sensors. Based on what you have already learned ROBOTC FEATURES 1 ft 1 ft 1 ft 1 ft 1 ft 2 ft ( note: 1 ft = 0.3048 m)

  19. Motors – 10 minute activity Here are a couple of suggestions Go straight for a fixed time (calculated by trial and error) Then turn right and go further straight for some more time (again calculated by trial and error) Then turn left and go straight OR Measure the circumference of the wheel to get how much the car will travel in one revolution. Use this number and the distances mentioned on the track to get the desired number of revolutions before turning Set the encoder accordingly and GO! OR Mix the above 2 methods ROBOTC FEATURES

  20. Sensor Interface • RobotC has an extremely powerful sensor interface which may be used to communicate with Lego and other third party sensors. • Ideally, RobotC sensor interface provides an enormous degree of freedom to the programmer. • It provides several options for configuring the sensor ports to • Read the raw value – Mainly used for self designed sensors • Communicate via the I2C interface – Mainly used by third party providers • Work using standard protocols and thresholds with the standard Lego sensors ROBOTC FEATURES

  21. Sensor Interface - Accessing The sensor interface in RobotC may be accessed through the Robot Menu on top of the IDE. The steps for accessing the sensor menu are as follows ROBOTC FEATURES Click on the Robot Button on the top menubar and select the Motors and Sensors Setup box

  22. Sensor Interface - Accessing Click on the management tab. This brings up the options to select the kind of sensors that are displayed ROBOTC FEATURES Tick the bottom 3 boxes. Unless you want to use old RCX Sensors

  23. Sensor Interface - Accessing A popup will occur as depicted. Choose the A/D sensor tab. A/D stands for Analog to Digital ROBOTC FEATURES Type of sensors You can configure up to 4 sensors Fields for specifying the names of the sensors

  24. Sensor Interface - Accessing Give a name to the sensors you intend to use and configure it to a certain type from the drop box ROBOTC FEATURES Type of sensors This one is being configured as SONAR names given to the three sensors

  25. Sensor Interface - Accessing Click on OK. This will create some auto-generated lines of code at the top of the program. This means that the sensors have been configured for use in the program. ROBOTC FEATURES Observe, No line numbers Auto-generated code. DO NOT EDIT THIS Given sensor names

  26. Sensor Interface - Accessing After configuration, using the sensor values in the program is a trivial task — two methods of obtaining the sensor values: myVar = SensorValue(sensor_name) myVar = SensorRaw(sensor_name) The first method returns the configured sensor value. Second one returns the raw value. Parameters sensor_name – This denotes the name assigned to the sensor in the configuration step Both may be used to obtain sensor readings (either raw or calibrated) The choice of method depends upon intended use ROBOTC FEATURES

  27. Sensor Interface Each sensor after configuration has two types of values Raw value – This is the raw value that the NXT observes based on the voltage across the input port. Every sensor has a raw value reading. Varies between 0-1023 (10 bits) Sensor Value – Obtained after application of thresholds to the raw value based on the configuration. Range depends on the configuration. More apt as per application Example: For a sensor configured as a touch sensor ROBOTC FEATURES

  28. Sensors – 10 min activity Configure the sensor on port 1 to be a light sensor. Write a snippet of code that looks at the sensor reading and displays a “Light!” or “Dark!” message on the NXT screen when the light sensor is over a light or dark surface. ROBOTC FEATURES

  29. Sensors – 10 min activity Did your program look like this?? #pragma config(Sensor,S1,LightSensor,sensorLightActive) //*!!Code automatically generated by 'ROBOTC' configuration wizard !!*// int lightvalue; task main() { while(true){ lightvalue =SensorValue(LightSensor); if(lightvalue >45) { nxtDisplayStringAt(1,20,"Light!"); }else{ nxtDisplayStringAt(1,20,"Dark!"); } } } ROBOTC FEATURES

  30. Debugging Debugging is one of the most difficult parts of writing code Fortunately, RobotC has an extremely powerful debugger, much better than other languages for similar functions ROBOTC FEATURES

  31. Debugger – Not Compiler Debugging generally refers to solving logical fallacies in the code. The compiler will give ERROR messages ONLY for syntax errors. You cannot run a code with syntax errors The compiler does highlight potential logical flaws in the form of WARNINGS and INFO messages. But these MAY or MAY NOT be the source of the logical problems. It is a good practice to make sure you have fixed all warning and info messages as well. ROBOTC FEATURES

  32. The Debugger Window Start/Stop Program Suspend (pause) or Resume Update debugger display windows (once) ROBOTC FEATURES Update display windows (continuously) Warning: Can slow program execution! Line-by-line code execution (see extra slides for more details)

  33. Debugging - Options Compiling and loading the program on the brick will enable several new debug options which were previously disabled or inactive Each of these windows is significant for a particular kind of error tracking The most important ones are 1. Global Variables 2. NXT Devices 3. Task Status ROBOTC FEATURES

  34. Debugging Windows } Global Variable Values ROBOTC FEATURES Sensor Values

  35. Debugging – 5 minute activity Using the program that you wrote in the last activity, use the debugger to observe the changing sensor values and the changing “lightvalue” variable as you move the NXT to different lighting conditions. ROBOTC FEATURES

  36. Summary • In the final section, you learned • RobotC specific keywords and usage • Sensor configuration and usage • Basic use of the debugger • This completes the basic tutorial on RobotC. • You should now be familiar enough with the basic concepts to build sufficiently complex systems SECTION SUMMARY

  37. Help • In case you need help • Have a look at http://www.robotc.net/teachingmindstorms/ • Use the in-built help in the IDE • Ask Google • If you are still stuck, ask your TF/TA!!! • …and like mentioned initially, always remember - your design and needs should guide the language and not the other way around!! SECTION SUMMARY

  38. Questions??? • QUESTIONS

  39. Debugging - Example Consider the example on the next slide for the purpose of debugging There are intentionally created errors in that program Lets see if they can be identified using the debugger ROBOTC FEATURES

  40. ROBOTC FEATURES

  41. Debugging What errors can be identified from here?? This variable is not being updated, so mustn’t be assigned ROBOTC FEATURES These variables have identical values assigned, but according to sensors; they should be different More clues …

  42. Lets see how accurate we were variable light_sensor is not assigned ROBOTC FEATURES variable dist_sensor is getting light_sensor reading Thus we were correctly able to identify all errors

  43. Debugging Lets see how the debugger looks with the corrected programs ROBOTC FEATURES All seem good and in correspondence PERFECT!!!

  44. Lets correct the program Observe the color of these X’s. Recall from yesterday. These are simple information messages. Why do you think they are reported? The compiler is trying to tell you that though you have declared and assigned these variables, you have not used them anywhere in the program. So it is trying to save your memory and flag potential errors. Sometimes, you tend to declare a variable with the intention of using it but end up using the wrong variable with a similar name. This can lead to really unpredictable results. One of the most difficult logical errors to catch ROBOTC FEATURES

  45. Debugging One of the major sources of problems is disconnection of an input sensor from the port, either due to a loose connection, or inadvertent connection to the wrong port In this example, the light sensor from port A is connected mistakenly to port C Observe how the raw value of port A is saturated at 1023 while there is an undesired value on port C ROBOTC FEATURES

  46. Debugging One common problem with many codes is missing timing delays. Such mistakes cause a lot of confusion and undesirable results These are difficult to catch by using the debugging techniques discussed They can be better examined by using the step by step debugger of RobotC ROBOTC FEATURES These commands allow step by step execution, hence giving more control for analysis

  47. Debugging - Example Consider a program that moves the car forward till the light sensor reading is above a threshold (i.e. it is bright). If it sees a shadow, or darkness, i.e. the value of the light sensor drops, it backs up for some distance and then tries again ROBOTC FEATURES This program has the error that as soon as the car sees the black line or black shadow, it stops rather than going back.

  48. Debugging - Example Lets try to use the debugger stepping to solve the problem. We can see that if we select continuous update of the values, then the green line moves extremely fast and we are unable to understand anything. ROBOTC FEATURES

  49. Debugging - Example The way around this is to suspend the program by clicking the suspend button. This pauses the execution of the program leaving all the variables and sensors intact The sensor readings and motor tachometer readings keep getting updated even in the suspend mode ROBOTC FEATURES Then click the step into button. This will cause the green line to be replaced by a yellow one which will stay on a specific statement You are now using the stepping mode of the debugger

  50. Debugging - Example Each successive pressing of the Step Into button will advance the program step by step ROBOTC FEATURES

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