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Petri-Nets - Real Time Systems - Exam, Exams of Computer Science

Jaypee University of Engineering & TechnologyComputer Science

Main points of this past exam are: Petri-Nets, Conflict, Inhibitor Arc, Self-Loop, Concurrency, Join, Real-Time System, Human Operators, Operator Errors, Real-Time System

Typology: Exams

2012/2013

Uploaded on 03/28/2013

bholaa
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Cork Institute of Technology
Bachelor of Science (Honours) in Software Development and Computer
Networking - Award
(NFQ – Level 8)
January 2007
Real-Time Systems
(Time: 2 Hours)
Instructions
Answer any THREE questions.
Note: Question 1 = 34 marks.
All other questions = 33 marks.
Real-Time Systems Reference Booklet
Available
Examiners: Dr. J. Creagh
Dr. J. Buckley
Dr. A. Kinsella
Q1. (a) (i) Describe the different types of Petri-Nets giving clear examples. (6 Marks)
(ii) With examples, clearly explain each of the following Petri-Net concepts:
- conflict
- inhibitor arc
- self-loop
- concurrency
- join
- split. (7 Marks)
(iii) “Petri-Nets are important for real-time system design”. Discuss, make points and
justify your points. (6 Marks)
(b) (i) HCI encourages design so that human operators find it difficult to make errors.
Referring to real-time systems, give examples of operator errors. What are the
HCI design principles that should be adhered to, to reduce the frequency of such
operator errors? Justify. (7 Marks)
(ii) Simulation may provide many advantages to real-time system testing. Give two
clear examples of where simulation would be required? What are the advantages
and disadvantages of simulation for real-time systems? (8 Marks)
pf3

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Cork Institute of Technology

Bachelor of Science (Honours) in Software Development and Computer

Networking - Award

(NFQ – Level 8)

January 2007

Real-Time Systems

(Time: 2 Hours)

Instructions Answer any THREE questions. Note: Question 1 = 34 marks. All other questions = 33 marks. Real-Time Systems Reference Booklet Available

Examiners: Dr. J. Creagh Dr. J. Buckley Dr. A. Kinsella

Q1. (a) (i) Describe the different types of Petri-Nets giving clear examples. (6 Marks) (ii) With examples, clearly explain each of the following Petri-Net concepts:

  • conflict
  • inhibitor arc
  • self-loop
  • concurrency
  • join
  • split. (7 Marks) (iii) “Petri-Nets are important for real-time system design”. Discuss, make points and justify your points. (6 Marks) (b) (i) HCI encourages design so that human operators find it difficult to make errors. Referring to real-time systems, give examples of operator errors. What are the HCI design principles that should be adhered to, to reduce the frequency of such operator errors? Justify. (7 Marks) (ii) Simulation may provide many advantages to real-time system testing. Give two clear examples of where simulation would be required? What are the advantages and disadvantages of simulation for real-time systems? (8 Marks)

Q2. (a) An automatic train system has the following safety sub-system. A distance sensor can detect accurately the distance of another train in front of our train. If the distance is greater than 500, then no action is taken by the safety sub-system. If the distance is less than 500, then the accelerator is disengaged. If the distance is less than 300, then the brakes are applied and the accelerator is disengaged. If the distance is less than 200, then the brakes are applied and the accelerator is disengaged. Also, the alarm is turned on. Sensor : Distance sensor Actuator : Brake, Accelerator, Alarm Write an ADA program to solve this problem. The distance sensor indicates a reading between 0..1000 and must be monitored every 0.5 seconds, with a deadline of 100 ms. For actuators, 1 = ON, 0 = OFF. Note: A register called ‘CSR’ controls hardware. Refer to the reference booklet. A second register ‘READING’ is provided for reading a value from a sensor. A third register ‘WRITING’ is provided for writing a value to an actuator. (22 Marks)

(b) Define the HRT-HOOD protected object. Also, with an outline example, show how the ADA language facilitates protected object implementation. (11 Marks)

Q3. (a) Referring to real-time systems, briefly define the following:

  • Reliability
  • Failure modes (giving examples of the different failure modes)
  • Assumptions about how a system may fail (giving examples of the different ways a system may fail) (7 Marks) (b) What are the 4 major sources of fault in a real-time system? Give an example of each. (6 Marks) (c) (i) Detail the function of the driver process with N-version programming. Example required. (6 Marks) (ii) Threshold values can cause problems for N-version programs. Explain with an example, and indicate a possible solution. (8 Marks) (d) Testing is a vital area for real-time system development. Most real-time systems must provide different types of fault tolerance. How does this impact on the testing process? Discuss. (6 Marks)