lejos NXJ Problem Solving with Robots [PRSOCO601]

Transcription

1 lejos NXJ Problem Solving with Robots [PRSOCO601] Thomas Devine February 20,

2 Contents 1 lejos NXJ Introducing the Java Development The Java Platform Introducing lejos NXJ Platform Installing NXJ Uploading the Firmware Compiling and Uploading Java Code using Command Prompt Eclipse Development Environment Installing a Development Environment Using Eclipse with lejos NXJ Loading a Project and Entering Code Compiling and Downloading Code Running the Program Creating a New Java Program Class

3 List of Figures 1 Java Development Process Java Virtual Machine Java Development Environment lejos NXJ Development Environment lejos Logo Eclipse Workspace lejos Toolbar New Java Class

4 1 lejos NXJ LEGO's own NXT-G programming language is great, especially for those just learning to program. However, we need to use Java to program the NXT to do things. This module uses the lejos NXJ, a software platform that allows you to program the NXT brick using Java. In this section we will briey discuss how to set up lejos NXJ on your computer, and introduce a time saving Integrated Development Environment (IDE). But rstly, some basics that must be understood. 1.1 Introducing the Java Development In the Java programming language, all source code is rst written in plain text les ending with the.java extension (e.g. MyProgram.java). Those source les are then compiled into.class les by the Java compiler (javac). A.class le contains bytecodes the machine language of the Java Virtual Machine (Java VM). The Java launcher tool (java) then runs your application using the Java Virtual Machine. Figure 1 shows this process. Figure 1: Java Development Process 1.2 The Java Platform A platform is the hardware or software environment in which a program runs. Some of the most popular platforms are Micro$oft Windows, Linux, Mac OS and even cell phones. Most platforms can be described as a combination of the operating system and underlying hardware. The Java platform diers from most other platforms in that it's a software-only platform that runs on top of other hardware-based platforms. The Java platform has two components:- the Java Virtual Machine (JVM), the Java Application Programming Interface (API) The Java VM (Figure 2) is available for many dierent operating systems { Micro$oft Windows, Linux, Macintosh and various cell phones. This means that any Java. class les are capable of running on either Micro$oft Windows, Linux, Mac OS or a compatible cell phone. The Java API is a large collection of ready-made software classes (3,777) that provide many useful capabilities (e.g. System, String, Scanner classes). It is organised into libraries of related classes known as packages. 4

5 Figure 2: Java Virtual Machine Figure 3 shows the relationship between a standard Java program MyProgram.class, the Java API, Java Virtual Machine, and Hardware-Based Platform. Notice how the API and Java Virtual Machine hide the program from the underlying hardware. Figure 3: Java Development Environment 1.3 Introducing lejos NXJ Platform lejos is pronounced like the Spanish word "lejos" (lay haws). lejos is Spanish for "far". The letters JOS are capitalised because those letters are an acronym for Java Operating System. Like the Java platform, the lejos NXJ platform is also a software-only platform that runs on top of other hardware-based platforms, but primarily the Lego NXT brick. The lejos NXJ platform has two components:- The lejos JVM, the NXJ Application Programming Interface (API) The lejos JVM is a tiny Java Virtual Machine written for the Lego NXT brick in The lejos JVM (Java Virtual Machine) is written in C code in a platform independent style, which means it is easily ported to other machines. So far it has appeared on the Lego RCX brick, the Nintendo's Gameboy Advance, and now the Lego NXT brick. 5

6 The NXJ API is a small collection of classes (365) that provide many useful capabilities such as input/output support, core Java classes, navigation, access to NXT sensors, motors, etc. It is also organised into libraries of related classes known as packages. Figure 4 shows the relationship between the Java NXT program GoForward.class, NXJ API, lejos Java Virtual Machine, and Lego NXT Brick. Figure 4: lejos NXJ Development Environment 1.4 Installing NXJ You receive the following when you download the Java SDK from Sun Microsystems: classes that allow you to interact with your computer, tools to compile code, a Java Virtual Machine to run your code. You get the same things when you download IeJOS NXJ, except that the class selection is tailored to the capacity and needs of the NXT brick. You do not need to install this software, it has been done for you. The NXJ software can be downloaded from the lejos website. 1.5 Uploading the Firmware At the moment the Lego NXT brick is using a Lego operating system (aka rmware) that handles the NXT-G programs you have been writing using the Lego NXT Software. However, we must replace this operating system (rmware) with lejos. To do this follow these steps (once only):- 1. First we need to place the NXT brick in rmware upload mode. The reset button is cleverly hidden in a LEGO pin hole so you don't accidentally press it. Turn on the NXT. Using a bent paperclip, insert it into the hole in the upper-right corner of the underside of the NXT brick. Hold the button for at least four seconds to erase the current rmware and put it into rmware upload mode. 2. Your NXT brick should be making a soft pulsing sound. Now we need to upload the rmware. Plug in your USB cable. Windows users can enter the command line by selecting Start> Run and then typing cmd (and click OK). At the DOS prompt type:- 6

7 X:\> nxjflash 3. After a very brief moment you will see the lejos NXJ logo (Figure 5) and a menu system will appear. Your NXT brick is now ready to accept Java code. Figure 5: lejos Logo 1.6 Compiling and Uploading Java Code using Command Prompt In this section you can try compiling and uploading some sample code from the command line. Windows users can enter the command line by selecting Start> Run and then typing cmd (and click OK). 1. From a command line prompt, change to the samples tune directory where you installed lejos:- X:\> C: C:\> cd \java\lejos_nxj\samples\tune 2. Compile the sample Java le:- C:\java\lejos_nxj\samples\tune> nxjc Tune.java 3. This creates a le called Tune.nxj, lejos bytecode. Now it is time to upload the this le. Plug in your USB cable. Turn on the NXT by pressing the orange button and type:- C:\java\lejos_nxj\samples\tune> nxj -r Tune 4. After a moment your should hear a tune play from your NXT brick. You have just compiled, uploaded and run your rst Java program onto the Lego NXT! 7

8 2 Eclipse Development Environment 2.1 Installing a Development Environment As we have seen, Java programming is possible with a text editor and a command line. However, it's easier to click on buttons to make things happen rather than typing commands and optional parameters. Also, most text editors don't have many features to help you enter code. It won't tell you when you've misspelled the name of a class or forgotten a bracket. (But in the author's opinion this isn't always a good thing). An IDE, or Integrated Development Environment, is a tool that allows you to enter, compile, and upload code to your NXT using simple buttons. You're probably using a IDE called jgrasp already. It also monitors code syntax, coloring your code so you can more easily identify the parts. This section suggests using a free, open source IDE for your lejos NXJ needs. One of the best open source IDE's is Eclipse by IBM. It's free, powerful, and easy to use. It can make sense to use a more advanced IDE when your code grows quite large. However, it may be a number of years until this can be justied for you. Again, you do not need to install Eclipse, it has been done for you. Eclipse software can be downloaded from the Eclipse website. 2.2 Using Eclipse with lejos NXJ To launch the Eclipse IDE Windows users can select Start> Programs> Programming> Eclipse. Eclipse stores data about your work in a workspace. For this module, you will create/use a workspace that is always stored on your X drive. When prompted tell Eclipse where to store your workspace. Figure 6 shows what you must type for your workspace and click the checkbox to get Eclipse to use this folder as the default workspace location. Figure 6: Eclipse Workspace 8

9 2.2.1 Loading a Project and Entering Code For now, we will load an existing Eclipse project called lejos HelloWorld. The project is stored in a ZIP le called lejos HelloWorld.ZIP on the Problem Solving with Robots webpage. Follow the steps outlined here to retrieve and load this project:- 1. Go to the Problem Solving with Robots webpage; 2. Right click on the le lejos HelloWorld.ZIP and Save As to the directory x:/workspace; 3. Unzip the le lejos HelloWorld.ZIP. You should now have a directory called lejos HelloWorld in the x:/workspace directory; 4. Now Import the project into Eclipse. From the Eclipse menu choose File> Import...; 5. From the Import Dialog choose General> Existing Projects into Workspace and click the Next button; 6. For the "Select root directory" textbox, click the Browse button and select the X:/workspace directory; 7. From the "Projects" list select the lejos HelloWorld project and click the Finish button; 8. You should now see a project called lejos HelloWorld in the left hand Navigation pane. You will be required to follow the steps above for every new project given to you. To enter code follow these steps:- 1. In the Eclipse navigation pane to the left single click on the lejos HelloWorld folder icon and from the menus select Project> Open Project. The lejos HelloWorld project is now open; 2. From the project folder icon select src> HelloWorld.java; 3. In the Code pane you should see some Java code. Change the string "message" in the LCD.drawString() method to "hello,world!" Compiling and Downloading Code We are now ready to compile the code. From the NXJ tools button in the Eclipse toolbar shown in Figure 7, select the item NXJ Compile. Next, turn on the NXT brick, plug in the USB cable, and select the item NXJ Download from the NXJ tools button. The code should download to the NXT brick followed by a few beeps from the NXT brick. 9

10 Figure 7: lejos Toolbar Running the Program Using the buttons on the NXT brick select Files> HelloWorld.nxj> Execute Program. You should see the text "hello, world" appear briey Creating a New Java Program Class Follow these instructions each time you are asked to write a new Java program in a Eclipse Project. 1. Select the project folder icon in the left hand pane; 2. Choose File> New> Class; 3. See Figure 8. In the New Java Class window type the program name in the Name: eld (e.g. BatteryProgram); 4. Click the checkbox labelled public static void main(string[] args); 5. Click the Finish button. 10

11 Figure 8: New Java Class References 11