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REAL TIME SYSTEM

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					REAL TIME SYSTEMS
RTOS focused on completing computational task within specified time interval. It focuses on meeting response rerquirement of an application.It permits user to create several processes within an application and Interleaved execution of these processes such that response requirement of application is met.

TYPES OF REAL TIME SYSTEM:
  Hard real time system Soft real time system

Hard real time systems are difficult to implement. But soft real time systems have low number of restrictions to implement in applications. Generally this real time system is mostly applied.

REAL TIME OPERATING SYSTEMS:
   VxWorks QoS Posix

RTOS Provides following facilities :
   Creation of multiple processes within application. Ability to design priorities to process. Programmer defines interrupts and interrupt processing routines. Priority driven or deadline oriented scheduling. Fault tolerance and graceful degradation

 

Designing Realtime Software
Designing Realtime software involves several steps. The basic steps are listed below: Software Architecture Definition Co-Design Defining Software Subsystems Feature Design Task Design

Task Design
Designing a task requires that all the interfaces that the task needs to support should be very well defined. Make sure all the message parameters and timer values have been finalized.

Selecting the Task Type
Once the external interfaces are frozen, select the type of task/tasks that would be most appropriate to handle the interfaces:

Single State Machine Multiple State Machines Multiple Tasks Complex Task

REAL TIME SYSTEM WORKING:
Real time software interacts with hardware interface by two ways.This hardware interface will get Inputs from environment and Acts through effectors to environment. It is likely Agent based actions in artificial intelligence

REAL TIME SYSTEM PERFORMANCE
Real time system performance data is basic one.It will be converted into archived performance data. Then it will be changed into Trends and projection mainly.Finally, it will be converted for modeling and decision support. After it will be given to real time system data again.

RealTime System Models
The RealTime System is available in several different packages. Each of these models has been specially designed to meet the requirements and specifications of specific areas of industry. Choose the model that fits your business’s needs or have us custom design a RealTime package that caters to your company’s unique demands.

RealTime Gallery
This version of RealTime is designed for galleries who carry unique products, which market perfectly on the Internet. Display your products online with complete descriptions, pictures, and information request forms. As with every RealTime model, this version is completely updateable by you from your PC, so you can add, delete, or edit listings as often as needed. RealTime Gallery gives you the power to market your one-of-a-kind pieces worldwide.

This diagram indicates the services provided by real time operating system.it manages communication,memory allocation, device I/O management and timingness.Task management involves all above things.

ISSUSE IN REAL TIME SYSTEM DESIGN
Designing Realtime systems is a challenging task. Most of the challenge comes from the fact that Realtime systems have to interact with real world entities. These interactions can get fairly complex. A typical Realtime system might be interacting with thousands of such entities at the same time.

    

Realtime Response Recovering from Failures Working with Distributed Architectures Asynchronous Communication Race Conditions and Timing

Realtime Response :
Realtime systems have to respond to external interactions in a predetermined amount of time. Successful completion of an operation depends upon the correct and timely operation of the system. For example, a telephone switching system must feed dial tone to thousands of subscribers within a recommended limit of one second.

REAL TIME SCHEDULING
According to priority the processes will be taken into execution.Real time systems use mainly two schedulings.  First come first serve [FCFS]  Round robin algorithm In design of real time systems three schedulings are mainly used. They are:  Static scheduling (schedulig is prepared before system is put into operation)  Priority based scheduling  Dynamic scheduling (decision will be taken when processes arrive)

This figure indicates the priority based scheduling in real time systems. High priority task will be taken first and then nested tasks will be taken according to priority.

Recovering from Failures
Realtime systems must function reliably in event of failures. These failures can be internal as well as external. The following sections discuss the issues involved in handling these failures.

Internal Failures
Internal failures can be due to hardware and software failures in the system. The different types of failures you would typically expect are:

Software Failures in a Task Processor Restart Handling Processor Failure Board Failure Link Failure
Invalid Behavior of External Entities: When a Realtime system interacts with external entities, it should be able to handle all possible failure conditions from these entities. A good example of this is the way a telephone switching systems handle calls from subscribers. In this case, the system is interacting with humans, so it should handle all kinds of failures, like: 1. Subscriber goes off hook but does not dial 2. Toddler playing with the phone! 3. Subscriber hangs up before completing dialing. Inter Connectivity Failure: Many times a Realtime system is distributed across several locations.

Working with Distributed Architectures

Most Realtime systems involve processing on several different nodes. The system itself distributes the processing load among several processors. This introduces several challenges in design:

Maintaining Consistency Initializing the System Inter-Processor Interfaces Load Distribution Centralized Resource Allocation

Asynchronous Communication
. The main reason is that most communication in the real world is asynchronous in nature, i.e. very few message interactions can be classified into the query response paradigm that works so well using RPCs.

Race Conditions and Timing
It is said that the three most important things in Realtime system design are timing, timing and timing . Realtime systems deal with timing issues by using timers. Timers are started to monitor the progress of events.

The main issue here is identifying race conditions. Most race conditions are not as simple as this one. Some of them are subtle and can only be identified by careful examination of the design.

REAL TIME APPLICATIONS:
It is an application which requires ‘timely’ response from computer system to prevent failures. Examples:     Guidance of missiles and satellites. Multimedia applications. Robotics Command and control applications [Air traffic control,Data sampling]

STEPS IN REAL TIME APPLICATIONS DEVELOPMENT :  Analyse application and determine whether late response to application can lead to failure.  Compute response requirement of appln.  Determine time required to execute each action.  Decide whether OS can provide timely response.  Install , deploy application using OS.

WIRELESS REAL TIME SYSTEM Real time system is mainly used in wireless network also.It is mostly used in application level.

CONCLUSION AND MY THINKING:
 REAL TIME SYSTEM IS MOST EFFICIENT ONE , SO WE ARE USING THIS MAKE WONDERFUL THINKS


				
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posted:1/25/2010
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