REAL TIME OPERATING SYSTEMS

(RTOS)

By :- Shibu krishnan

What is an Operating System?

A more formal definition!

Operating system is a piece of software which controls all the computer’s resources and provides the base upon which the application programs can be written

Where your OS sits in your System?

compilersdatabasesword processors

CPUmemoryI/O devices

TYPES OF OPERATING SYSTEMS

Stand-Alone Operating systemNetwork Operating systemsEmbedded Operating systems

Stand-Alone Operating system

It is a complete operating system that works on a desktop or notebook computer. Examples of stand-alone operating systems are:DOSWindows 2000 professionalMac OS X

Network Operating systems

It is an operating system that provides extensive support for computer networks. A network operating system typically resides on a server. Examples of a network Operating system are:Windows 2000 serverUnixLinuxSolaris

Embedded Operating system

You can find this operating system on handheld computers and small devices. It resides on a ROM chip. Examples of embedded operating systems are :oWindows CEoPocket PC 2002oPalm OS

What is RTOS?A real-time operating system (RTOS) that supports real-time applications and embedded systems. Real-time applications have the requirement to meet task deadlines in addition to the logical correctness of the results.

Multiple events handled by a single processor

Events may occur simultaneously

Processor must handle multiple, often competing events

Difference between a General purpose operating system(GPOS) and an RTOS

A GPOS is used for systems/applications that are not time critical. 

In the case of a GPOS – task scheduling is not based on  “priority”,it is programmed to achieve high throughputA GPOS is made for high end, general purpose systems whereas RTOS is usually designed for a low end, stand alone device All the process and threads in RTOS has got bounded latencies – which means –a process/thread will get executed within a specified time limit.

Classification real time systems(RTS)

Hard Real Time System

Firm Real Time System

Soft Real Time System

Hard Real time:

Here missing an individual deadline results in catastrophic failure of the system which also causes a great financial loss . The examples for Hard real time systems are: Air traffic control Nuclear power plant control

Firm Real time:

In this, missing a deadline results in unacceptable quality reduction. Technically there is no difference with hard Real time, but economically the disaster risk is limited. Examples for Firm real time are :Failure of Ignition of a automobileFailure of opening of a safe

Soft real time:

Here the dead line may not be fulfilled and can be recovered from. The reduction in system quality and performance is at an acceptable level. Examples of Soft real time systems :Multimedia transmission and reception Networking, telecom (Mobile) networks websites and servicesComputer games

Features of an RTOS: •Context switching latency should be short. This means that the time taken while saving the context of current task and then switching over to another task should be short.

•The time taken between executing the last instruction of an interrupted task and executing the first instruction of interrupt handler should be predictable and short. This is also known as interrupt latency.

•Similarly the time taken between executing the last instruction of the interrupt handler and executing the next task should also be short and predictable. This is also known as interrupt dispatch latency.

•Reliable and time bound inter process mechanisms should be in place for processes to.

•Similarly the time taken between executing the last instruction of the interrupt handler and executing the next task should also be short and predictable. This is also known as interrupt dispatch latency.

•Reliable and time bound inter process mechanisms should be in place for processes to communicate with each other in a timely manner.

•An RTOS should have support for multitasking and task preemption. Preemption means to switch from a currently executing task to a high priority task ready and waiting to be executed.

•RTOS should be fault tolerant

Some of the most widely used RTOS are:- •LynxOS•OSE•QNX•RTLinux•VxWorks•Windows CE

Programming languages Used

C is most widely used in RTOS programming

C++ and Ada are the next more popular for large projects.

Java may also be a choice for some applications

Thank you