24-12-2012, 02:12 PM
SEMINAR REPORT ON RELIABILITY OF REAL TIME EMBEDDED SYSTEM
REAL TIME EMBEDDED SYSTEM.docx (Size: 160.43 KB / Downloads: 125)
ABSTRACT
A system is not reliable by chance. Often much effort and resources are spend to achieve reliability. The developers, often of many disciplines, each contribute in the development of a highly reliable product. In their design and implementation, reliability is a self-evident ambition which forms the basis of good engineering practices. In practice, reliability can be seen as the result of a large number of explicit and implicit control activities, properties and measures, often deeply entangled in the professional engineering knowledge of the experts involved.
Reliable according to well-known dictionaries means: that can be trusted upon with confidence.As the capability and complexity of embedded systems increases, so does the challenge of ensuring they perform reliably. Just as PCs and servers must be protected from malicious code and external attacks, so too must embedded systems.
The challenge becomes even more complex when these systems are charged with performing multiple tasks or running a range of different software applications, as is already the case in mobile phones. Each must be designed so that, if one function is compromised, the others can continue to run normally.Multiple sectors and industries are motivated to deliver secure embedded solutions. Yet, historically, embedded system security has been the focus of a limited set of embedded solutions. Today, embedded system designers are facing pressure to increase the level of security and privacy protection in the system while simultaneously driving down cost and reducing time to market. These embedded security solutions must also be flexible enough to adapt to the unique implementation of each embedded system.
EMBEDDED SYSTEM
An embedded system is a computer system designed for specific control functions within a larger system, often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal computer (PC), is designed to be flexible and to meet a wide range of end-user needs. Embedded systems control many devices in common use today.
Embedded systems contain processing cores that are either microcontrollers or digital signal processors (DSP). The key characteristic, however, is being dedicated to handle a particular task. Since the embedded system is dedicated to specific tasks, design engineers can optimize it to reduce the size and cost of the product and increase the reliability and performance.
Some key characteristics of embedded system:
Computing system with tightly coupled hardware and software integration that are designed to perform a dedicated function.
Usually a embedded part of larger system, known as embedding system, multiple embedded system can coexist in an embedding system.
Tightly-constrained -Low cost, low power, small, fast , perform function fast enough etc.
Hardware and software coexist –The software written for embedded system is often called firmware, is stored in read only memory or flash memory chips rather than hard drive.
contain processing cores that are either microcontrollers or digital signal processors (DSP).
REAL TIME EMBEDDE SYSTEM
The correctness of the system depends not only on the results of computations, but also on the time at which the results are produced , is called Real time embedded system.
Each real-time task is associated with some time constraints, e.g. a Deadline.
HARD REAL TIME SYSTEM
A system is said to be hard real-time if the correctness of an operation depends not only upon the logical correctness of the operation but also upon the time at which it is performed. An operation performed after the deadline is, by definition, incorrect, and usually has no value or to result in a catastrophic event. The cost of such catastrophe is extremely high and can involve human lives.
Many hard real-time systems are safety-critical. The task deadlines are of the order of micro or milliseconds.
Examples
Industrial control applications.
Anti- Missile System.
Robots.
Avionics.
Nuclear reactors.
Traffic signal controllers.
Anti-Lock brake systems.
Manufacturing plant controllers.
Medical devices.
FIRM REAL TIME SYSTEM
If a deadline is missed occasionally, the system does not fail, The results produced by a task after the deadline are rejected.
Examples
A video conferencing application.
A telemetry application.
Satellite-based surveillance applications.
SOFT REAL TIME SYSTEM
A real-time system in which a missed deadline does not compromise the integrity of the system or result in a catastrophic event. Only the performance of the system is said to have degraded. The utility of a result decreases with time after the deadline but costs can rise in proportion to the delay, depending on the application.
Example
Railway reservation system.
Web browsing.
In fact, all interactive applications.
Set Top Boxes.
Consumer Electronics.
ARCHITECTURE OF EMBEDDED SYSTEM
SENSOR
A Sensor is a device that respond to a physical stimulus (as heat light sound magnetism or a particular motion ) and transmits a resulting impulse (as for measurement or operating a control A sensor converts some physical characteristic of its environment into electrical signals.
ACTUATOR
A actuator is a mechanical device for moving or controlling something. Actuator converts electrical signals from a computer into some physical actions .The physical actions may be motion, change of thermal, electrical or physical characteristics of some object.
CRITICAL SYSTEM
Critical systems are those systems whose failure could result in loss of life, cause significant property damage or cause damage to the environment. These complex systems tend to have sufficient kinetic or potential energy which can become uncontrollable and thus pose a hazardous condition. Therefore, these systems must be designed in such a way as to guarantee system stability during all of the system operational modes. Furthermore, when a fatal fault occurs, the system safely shuts down.
SAFETY-CRITICAL SYSTEMS
Failure results in loss of life, injury or damage to the environment.
Chemical plant protection system.
MISSION-CRITICAL SYSTEMS
Failure results in failure of some goal-directed activity.
Spacecraft navigation system.
BUSINESS-CRITICAL SYSTEMS
Failure results in high economic losses.
Customer accounting system in a bank.
RELIABILITY CONCEPTS
Reliable according to well-known dictionaries means: that can be trusted upon with confidence. Software and hardware must be operational to fulfil user requirements. Design faults (bugs) must be taken out which results in maturity, whenever faults have not been detected they may cause a product to fail. If a product is fault tolerant it means that faults are caught in time by the product itself and failures are prevented. Whenever a failure is occurring it is most important to get the product operational again, which is called recoverable.