Concepts of Real time Systems (RTS)
- 1. Real Time System (RTS) The Islamic University Department of Computer Technical Engineering Third Class Lecturer Asst. Lec. Karrar Shakir Muttair ALNomani المحاضرهاالولى (النظري) 2019-2020
- 2. Contents Concepts of Real time Systems (RTS) Characteristics of RTS Types of RTS Comparison between Types of RTS Applications of RTS Challenges of RTS 2
- 3. Concepts of Real time Systems(RTS) 3 Real-time is a quantitative notion of time measured using a physical clock. Example: After a certain event occurs (temperature exceeds 50 degrees) the corresponding action (coolant shower) must complete within 100 mSec. System: As system is a mapping of a set of inputs into a set of outputs. When the internal details of the system are not of interest, the mapping function can be considered as a black box with one or more inputs entering and one or more outputs existing the system Figure 1.1. Figure 1.1: A system with (n) inputs and (m) outputs.
- 4. 4 Terms Associated with RTS The response-time is the time between the presentation of a set of inputs to a system and the realization of the required behavior, including the availability of all associated outputs, is called the response time of the system. A real-time system must satisfy response-time constraints or risk severe consequences. A failed system is a system that cannot satisfy one or more of the requirements stipulated in the formal system specification. Real time system means that the system is subjected to real time, i.e., response should be guaranteed within a specified timing constraint or system should meet the specified deadline. For example: flight control system, real time monitors etc. Concepts of Real time Systems(RTS)
- 5. 5 Job : A job is a small piece of work that can be assigned to a processor and may or may not require resources. Tasks: A set of related jobs that jointly provide some system functionality. Release time of a job: It is the time at which job becomes ready for execution. Execution time of a job: It is the time taken by job to finish its execution. Deadline of a job: It is the time by which a job should finish its execution. Deadline is of two types: 1. Relative deadline: Deadline - Release time. 2. Absolute deadline is equal to its relative deadline plus its release time. Absolute deadline= release time + relative deadline Response time of a job: It is the length of time from release time of a job to the instant when it finishes (Completion time). Response time of a job= Completion time - Release time Terms Associated with RTS
- 6. 6 Terms Associated with RTS Released time = 3 Relative deadline = Deadline - Release time = 10 – 3 = 7 Absolute deadline = release time + relative deadline = 3 + 7 = 10 Response time = Completion time - Release time = 9 – 3 = 6 Figure 1. 2: Descriptive example for some terms of RTS.
- 7. A Basic Model of RTS 7 Figure 1. 3: A Physical Model of a Real-Time System. Figure 1. 4: A Model of a Real-Time System.
- 8. A Basic Model of RTS 8 Sensor: A sensor converts some physical characteristic of its environment into electrical signals. An example of a sensor is a photo-voltaic cell which converts light energy into electrical energy. Actuator: An actuator is any device that takes its inputs from the output interface of a computer and converts these electrical signals into some physical actions on its environment. The physical actions may be in the form of motion, change thermal, electrical. A popular actuator is a motors, heaters or pneumatic. Signal Condition Units: The electrical signals produced by a computer can rarely be used to directly drive an actuator. The computer signals usually need conditioning before the can be used the actuator. This is termed output conditioning. Similarly, input conditioning is required to be carried out on sensor signal before they can be accepted by the computer this is termed input conditioning. Interface Unit: The interface takes care of buffering and the handshake control aspects. Analog to digital conversion are used in input interface and digital to analog conversion are used in an output interface.
- 9. Overall Structure of RTS 9 AS shown on the Figure 1.5 the overall structure of RTS consists of: Hardware: (CPU, I/O devices, memory… etc.) A real time Operating System: function as standard OS, with predictable behavior and well-defined functionality. A collection of RT tasks/processes: (share resources, communicate/ synchronize with each other and the environment). Figure 1.5: Overall structure of RTS.
- 10. Characteristics of RTS 10 1. Time constraints. 2. New Correctness Criterion. 3. Embedded. 4. Safety-Reliability. 5. Concurrency. 6. Distributed and Feedback Structure. 7. Task Criticality. 8. Custom Hardware. 9. Reactive. 10. Stability. 11. Exception Handling.
- 11. Important Characteristics 11 1.Safety 2.Reliability Safety and reliability are related but distinct. 1. Safety is concerned with ensuring system cannot cause damage irrespective of whether or not it conforms to its specification. 2. Reliability is concerned with conformance to a given specification and delivery of service. A safe system: • Does not cause damage even when it fails. A reliable system: • Operates for long time without any failure.
- 12. Types of Real-Time Systems 12 Real-time systems are different from other systems: Tasks have deadlines associated with them. A real-time task can be classified into either hard, soft, or firm real- time task depending on the consequences of a task missing its deadline. 1. Hard real-time systems 2. Soft real-time systems 3. Firm real-time systems
- 13. 13 Hard Real-Time Systems Time is very important and achieving the desired result is also important. But if the target is achieved without time commitment, it means system failure. Many of these systems are considered to be safety critical. An exceeds in response time leads to potential loss of life and/or big financial damage. Sometimes they are “only” mission critical, with the mission being very expensive. In general there is a cost function associated with the system. Hard Real-Time System Examples Car airbag. Anti lock breaking system (ABS). Air craft control system.
- 14. Soft Real-Time Systems 14 There are time limits, but they can be tolerated. The mistakes here do not lead to the damage of the system. And do not cause a disaster. There is a cost associated to overrunning, but this cost may be abstract. Often connected to Quality-of-Service (QoS). Soft Real-Time Systems Video processing. Digital camera. Mobile phones.
- 15. 15 Comparison between Hard RTS and Soft RTS Characteristics Hard RTS Soft RTS Response Time Hard- Required Soft - Required Peak Load Performance Predictable Degraded Controlled by Environment Computer Safety Critical Non Critical Size of Data Small Large Error Detection Autonomous User Assisted Hard RTS Vs. Soft RTS
- 16. 16 Firm Real-Time System Systems which are soft real-time but in which there is no benefit from late delivery of service (which means a few missed deadlines will not lead to total failure, but missing more than a few may lead to complete and catastrophic system failure). The computation is obsolete if the job is not finished on time. Cost may be interpreted as loss of revenue. Typical example are prediction systems. Firm Real-Time System Examples Video conferencing. Satellite-based tracking of enemy movements.
- 17. Applications of RTS 17 Metal industry applications (Mechanical and Manufacturing Engineering). Electric utility monitoring and control applications (Electrical Power Engineering). Water plants applications (Civil and Environmental Engineering). Aviation and space applications (Aeronautical Engineering). Data Communication Applications (Electrical and Computer Engineering). Petrochemical applications (Chemical Engineering, Petroleum Engineering).
- 18. 18 Applications of RTS Figure 1.6: Disciplines that impact on Real Time System Engineering Real-Time Systems Control Theory Programming Languages Operations Research Algorithms Queuing Theory Operating Systems Software Engineering Computer Architecture Data Structures
- 19. Challenges of RTS The design and implementation of real-time systems requires attention to numerous problems. These include: 1. The selection of hardware and software. 2. Determine specification and design of real-time systems and correct representation of temporal behavior. 3. Understanding the nuances of the programming language (s) and the real time implications resulting from their translation into machine code. 4. Maximizing of system fault tolerance and reliability through careful design. 5. The design and administration of tests. 6. Finally, measuring and predicting response time and reducing it. 19
- 20. Thank you for your attention!