Contents 1. Concepts of Real time Systems (RTS) 2. Characteristics of RTS 3. Types of RTS 4. Comparison between Types of RTS 5. Applications of RTS 6. Challenges of 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
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3. Concepts of Real time Systems(RTS)
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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
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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
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 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
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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
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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
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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
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 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

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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
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 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.

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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

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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
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 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).

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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.
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20. Thank you for your attention!