Real-Time Java: LAB #2 RealTime Threads: Scheduling & Release Models

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1 Real-Time Java: LAB #2 RealTime Threads: Scheduling & Release Models The goal of this lab is to learn how to use the two types of RTSJ schedulable entities: RealtimeThread and AsyncEventHandler and to understand their release(activation) and scheduling models. Exercise 1. The creation of a real-time thread. In this exercise you will create a single oneshot real-time thread using the RTSJ RealtimeThread class. The cost of the task corresponds to the duration of the execution of the run() method. You will affect a priority value of 15 to the thread T1 (using the PriorityParameters class). The just executes 3 loops. It is important to observe and note the real duration of this execution. Question: Could such a thread be qualified as a real-time thread? public class OneRTT { public static final int NB_IT = ; RealtimeThread t1 = new RealtimeThread(new PriorityParameters(15)) { RConsole.println("Enter in thread1!"); RConsole.println(«Context Switch Delay: "+ Long.toString(start1-deb) ); ; RConsole.println(«Starting T1 at: " + Long.toString(start1-deb)); RConsole.println(«Duration of T1 : " + Long.toString(end1-start1)); RConsole.println(" end of T1 *"); RConsole.println(«Starting»); t1.start(); Page 1

2 try { t1.join(7000); catch (InterruptedException ie) {; RConsole.close(); Exercise 2. Creation of a Periodic realtime thread. You will modify the creation of the real-time thread T1 to add a PeriodicParameters object. This object is used to set: Offset, Period, Cost, Deadline of the new thread. Run the program and observe its real duration and its real period. do { Bla bla bla while (waitfornextperiod()); Question: Do the observed values match the set values? Question: Do the observed values match the set values? Question: What is the LejosRT behavior associated to a CostOverrun fault and to a DeadlineMISS failure? public class OneRTTPeriodic { public static final int NB_IT = ; RealtimeThread t1 = new RealtimeThread(new PriorityParameters(15),new PeriodicParameters( new RelativeTime(0,0), /* OFFSET */ new RelativeTime(5000,0), /* PERIOD */ new RelativeTime(2000,0), /* COST */ new RelativeTime(5000,0), /* DEADLINE */ null, null)) { int i=0; do{ RConsole.println("Entering 1!!!!!!!"); RConsole.println("Delai de preemption : "+ Long.toString(start1-(deb+i*5000)) ); RConsole.println("Starting 1 : " + Long.toString(start1-deb)); RConsole.println(«Duration of 1 : " + Long.toString(end1-start1)); i++; RConsole.println(«Ending 1 *******"); while(waitfornextperiod() && i<3); ; RConsole.println("Debut"); Page 2

3 t1.start(); try { t1.join(20000); catch (InterruptedException ie) {; RConsole.close(); Exercise 3. The scheduling of two periodic realtime threads 1. The two threads are executed at the same priority level. You will create 2 periodic real-time threads with the same Priority (15), Cost (5000 ms), Period (5000ms) and relative Deadline (50000 ms). What is the Scheduling Policy in this case? 1. The two threads are started at different times and executed at different priority levels. See the task values in the following table. What is the Scheduling Policy in this case? Do you observe the preemption phenomenon? Task Priority Activation Time Cost Period Deadline Tau Tau Exercise 4. Driving a Motor and a Wheel This exercice is a a concrete approach for a periodic real-time task. Take a motor and a wheel. Imagine the wheel is used to move a Robot. The movement is periodic, the Robot move forward for 2 meters each 10seconds. To implement that behavior you need a periodic real-time thread. You need to use the MotorPort class. Page 3

4 The Tachometer is an instrument measuring the rotation of a wheel. The gettachocount() method returns the number of degrees of rotation of the wheel. You must reset the Tachometer before you use it. MotorPort.A.resetTachoCount(); The controlmotor() method is used to start the motor. Two parameters: POWER (0-100) and FUNCTION (1=Forward; 2=Backward; 3=Stop). In the following exemple the motor starts and run until the wheel achieves 10 rotations. MotorPort.A.controlMotor(100, 1); while (MotorPort.A.getTachoCount() <= 3600) { MotorPort.A.controlMotor(0, 3); Question: what is the cost of the thread? Question: what s happen if you reduce the power of the motor? Exercise 5. Creation of an Event Driven Entity (AsyncEventHandler). In this exercise you will create a periodic real-time thread. You create an asynchronous event (ASYNCEVENT) Dans cet exercice, vous allez créer une tâche périodique et une tâche apériodique de priorité plus élevée. La tâche apériodique sera activée par la tâche périodique (au milieu de l exécution de cette dernière). Vous allez observer la préemption de la tâche périodique par la tâche apériodique. L activation de la tâche apériodique se fait via un appel a la méthode fire() sur un objet Event. Le ou les handlers associés (addhandler()) est ou sont activés. Les handlers seront exécutés en respect de leur priorité. To use an AsyncEventHandler: 1. Create an AsyncEvent 2. Create an AsyncEventHandler 3. Associate the Handler with the Event 4. Fire the Event (the Handler will be activated). import lejos.nxt.comm.*; import lejos.realtime.*; import lejos.nxt.*; public class ThrAperiod { public static final int NB_IT = ; public static long start2; public static long end2; public static AsyncEventHandler a; public static AsyncEvent aeh; Page 4

5 a = new AsyncEventHandler(){ public void handleasyncevent(){ RConsole.println("Entering the handler!»); start2=system.currenttimemillis(); RConsole.println(«Handler execution starts at : "+(start2-deb) +" du debut. "); ; end2=system.currenttimemillis(); RConsole.println(«Handler Duration : " + Long.toString(end2-start2)); RConsole.println(«End of the Handler "); a.setschedulingparameters(new PriorityParameters(25)); ae= new AsyncEvent(); ae.addhandler(a); RealtimeThread t1 = new RealtimeThread(new PriorityParameters(15),new PeriodicParameters( new RelativeTime(0,0), new RelativeTime(6000,0), new RelativeTime(2000,0), new RelativeTime(6000,0), null, null)) { ; int i=0; do{ RConsole.println(«Entering thread 1!"); ae.fire(); RConsole.println("Starting 1 : " + Long.toString(start1-deb)); RConsole.println(«Duration of 1 : " + Long.toString(end1-start1)); i++; RConsole.println(«End of 1 *******"); while(waitfornextperiod() && i<3); RConsole.println(«Starting Main"); t1.start(); try { Thread.sleep(1000); catch (InterruptedException ex) {; t1.join(10000); Question: Could such a Handler be qualified as a real-time Handler? Question: You modify the priority of the Handler from 25 to 12. What s happen? Exercise 6. Creation of a CostOverrunHander Apply the preceeding technic to create a CostOverrunHandler and associate it to the MotorThread. The CostOverrun handler will stop the wheel when a costoverrun event occurs. To generate the costoverrun event slow down the wheel (or block it). Page 5