rtos document

8/6/2019 RTOS Document

http://slidepdf.com/reader/full/rtos-document 1/10

Information Search Analysis Skill (ISAS)6/2/2011

INDEXINDEX

1/10By: Mukul Garg




1. Introduction………………………………….3

2. Types of RTOS……………………………...4

3. Scheduling in RTOS…………………………5

4. Memory Management in RTOS…………......65. Applications of RTOS……………………….7

6. Example of RTOSes………………………..8

7. Summary ……………………………………9

8. Bibliography……………………………….10

INTRODUCTIONINTRODUCTION

2/10By: Mukul Garg




First of all we need to know what an operating system is. In nutshell, anoperating system is system software that is used to control the system. There arevarious flavors of operating system, such as, batch operating system,multiprogramming operating system, time-sharing operating system, real-timeoperating system, parallel system, and many more. One of them, here we will

discuss some points about real-time operating system or RTOS.A real-time system is used when rigid time requirement have been placed on

the operation of a processor or the flow of data; thus, it is often used as a controldevice in a dedicated application. Sensors bring the data to the computer. Thecomputer must analyze the data and possibly adjust controls to modify thesensor inputs. Systems that control scientific experiments, medical imagingsystems, industrial control systems, and certain display system are real timesystem. Some automobile-engine fuel-injection systems, home appliancecontrollers, and weapon system are also real-time systems.

A real-time system has well-defined, fixed time constraints. Processing must bedone within the defined constraints, or the system will fail. For instant, it would bea robot arm to be instructed to halt after it had smashed into the car it wasbuilding. It functions correctly only if it returns the correct result within its timeconstraints.

Modern computer system also support real-time functionality like, support of multimedia, interactive graphics, task scheduler, and many other functionalitiesare applicable only in the environment that support soft real-time functionality.Not only PCs and PCs’ operating systems like Windows XP, but many other systems also support real-time functionality such as: antiaircraft systems,manufacturing companies where various work is done with the help of robots,many automobiles companies and other daily life things like many modern

engine of automobiles, microwave ovens etc.

TYPES OF RTOS TYPES OF RTOS

Real-time systems come in two flavors: hard and soft.

3/10By: Mukul Garg




1. Hard Real-Time System: A hard real-time system guarantees that criticaltask be completed on time. This goal requires that all delays in the systembe bounded, from the retrieval of stored data to the time that it takes theoperating system to finish any request made of it. Such time constraintsdictate the facilities that are available in hard real-time systems.

Secondary storage of any sort is usually limited or missing, with datainstead being stored in short-term memory or in read-only memory (ROM).Most advanced operating system features are absent too, since they tendto separate the user from the hardware, and that separation results inuncertainty about the amount of time an operation will take. For instant,virtual memory is almost never found on real-time systems. None of theexisting general-purpose operating system support hard real-timefunctionality.

2. Soft Real-Time System: A less restrictive type of RTOS is a soft real-time system, where a critical real-time task gets priority over other tasks,and retains that priority until it completes. As in hard real-time systems,

the operating system kernel delays need to be bounded: A real-time taskcannot be kept waiting indefinitely for the kernel to run it. Soft real time isan achievable goal that can be mixed with other types of systems.However soft real time system have more limited utility than hard realtime. Given their lack of deadline support, they are risky to use for industrial control and robotics. They are useful, however in several areas,including multimedia, virtual reality, and advance scientific projects –suchas undersea exploration and planetary rovers. These systems needadvanced operating system features that can not be supported by hardreal-time systems. Because of the expanded uses of soft real-timefunctionality, it is finding its way into most current operating systems,

including major versions of UNIX.

SCHEDULING IN RTOSSCHEDULING IN RTOSReal-time computing divides into two types. Hard real-time systems are requiredto complete a critical task within a guaranteed amount of time. Generally, aprocess is submitted along with a statement of the amount of time in which itneeds to complete or perform I/O. The scheduler then either admits the process,guaranteeing that the process will complete on time, or reject the request as

4/10By: Mukul Garg




impossible. This is known as resource reservation. Such a guarantee requiresthat the scheduler know exactly how long each type of operating system functiontakes to perform, and therefore each operation must guaranteed to take amaximum amount of time. Therefore, hard real-time systems are composed of special-purpose software running on hardware dedicated to their critical process,

and lack the full functionality of modern computers and operating systems.Soft real-time computing is less restrictive. It requires that critical processesreceive priority over less fortunate ones. The result is that the functionalities like,support of multimedia, high-speed interactive graphics, and variety of tasks likethat are available only in the environments that support soft real-timefunctionality. Implementing soft real-time functionality requires careful design of the scheduler and relative aspect of the operating system. The system must havepriority scheduling, and real-time processes must have the highest priority.

Various scheduling algorithms:

Rate Monotonic (RM)

Earliest Dead-Line First (EDF)

Minimum Laxity First (MLF)

Maximum Urgency First (MUF)

MEMORY MANAGEMENT IN RTOSMEMORY MANAGEMENT IN RTOS

A hard real-time system guarantees that a critical task will be completed in given

time constraint or the system will fail. In hard real-time system there is morecomplex and hard time constraint. Such time constraints dictate the facilities thatare available in hard real-time system. Secondary storage of any sort is usuallylimited or missing, with data instead being stored in short-term memory or inread-only memory (ROM). Virtual memory is almost never found in real-timesystem.

On the other hand, soft real-time system is less restrictive. In soft real-timesystem a real-time task get priority over other tasks. Soft real-time system can be

5/10By: Mukul Garg




mixed with other type of systems. Many modern operating systems now supportsoft real-time functionality. There are two types of memory management.

The first type is used to provide tasks with temporary data space. The system’sfree memory is divided into fixed sized memory blocks, which can be requestedby tasks. When a task finishes using a memory block it must return it to the pool.

A pool of memory is dedicated to high priority tasks and another to low prioritytasks. The high-priority pool is sized to have the worst-case memory demand of the system. The low priority pool is given the remaining free memory. If the lowpriority tasks exhaust the low priority memory pool, they must wait for memory tobe returned to the pool before further execution

The second type of memory management is used to dynamically swap code inand out of main memory. Specific techniques are memory swapping, overlays,multiprogramming with a fixed number of tasks (MFT), multiprogramming with avariable number of tasks (MVT) and demand paging.

Note: In case of swapping a process is divided into various numbers of pages.And pages are loaded into main memory one-by-one. So that large sizeprocesses can be executed on the system. When using overlays, the code ispartitioned into smaller pieces, which are swapped from disk to memory. In MFT,a fixed number of equalized code parts are in memory at the same time. Asneeded, these parts are overlaid from disk. MVT is similar to MFT except that thesize of the partition depends on the needs of the program in MVT. In the of demand paging processes are broke down in the number of pages and loadedinto memory as and when required.

APPLICATIONS OF RTOSAPPLICATIONS OF RTOS

Unlike the fundamental definition of RTOS, typical applications of real-time

systems have changed over the years. In 1980s real-time systems were usedalmost exclusively for control applications. Over the time the use of real-timesystems grew. Control applications remain popular, however. A source from1990s explains that in many real-time systems:

“Sensor brings data to the computer. The computer must analyze the data andpossibly adjust control to modify the sensor inputs. System that control scientificexperiments, medical imaging systems, industrial control systems and some

6/10By: Mukul Garg




display systems are real-time systems. Also included are some automobile-engine fuel-injection systems, home-appliance controllers and weapon systems”

-- (Operating System Concept –Silberschatz, Galvin)

Today there are various applications that require their output in fixed time, suchas weapons, embedded industry, and so many. Consider the followingapplications of RTOS,

RTOS for complex, hard real-time applications that require fast and

deterministic response, LynxOS. LynxOS is scalable RTOS from large andcomplex switching system down to small embedded products.

General purpose RTOS in embedded industry, VxWork. VxWork is

a component of Tornado II.

Windows CE 3.0, a highly modular embedded RTOS for small

footprint, mobile 32-bit intelligent connected devices. Windows CE can

work on 12 different processor architectures. It can be customized to meetspecific product requirement with a minimum footprint of 400MB.

RTOS for Java platform. The Jbed RTOS package is a real-time

capable virtual machine developed for embedded systems and Internetapplications under the Java platform. It allows an entire applicationincluding the device drivers to be written using Java. Instead of interpreting the bytecode, the Jbed RTOS translates the bytecode to fastmachine code prior to downloading or class loading. Jbed runs on 32-bitmicroprocessors and controllers. Jbed Light is smaller, low-cost versionfor fast and precompiled standalone applications. It contains the basiccomponents including the core Jbed virtual machine, a small set of standard Java libraries, and the Jbed libraries required to directly accessperipherals.

Real-time features are also supported by modern operating

systems, like Windows NT, Windows XP, and Native UNIX etc.

EXAMPLES OF RTOSEXAMPLES OF RTOS

BeOS

ChorusOS

eCos

FreeRTOS

ITRON

LynxOS

7/10By: Mukul Garg




MicroC/OS-II

OS-9

OSE

OSE/VDX

pSOS

QNX

RSX-11

RT-11

RTOS-UH

VRTX

VxWorks

Windows CE

RTLinux

RTAI

SUMMARYSUMMARY

Operating systems are use to control the system because they can do that inmuch better way than human beings. Real-time operating system in on of the

operating system that is use when there is rigid time requirements on theoperation of processor or flow of data, so often used as a controller. They have afixed and well defined time constraint and the work must be done within that timeconstraint or the system will fail. Various areas where RTOS are used areweapon system; multimedia, embedded industries and many modern generalpurpose operating systems also support real-time facilities.

Real-time system comes into two flavors: hard real-time system and soft real-time system. Hard real-time system guarantees that critical task get completed

8/10By: Mukul Garg




within the defined time constraint. This requires that all the delays must bebounded from the retrieval of the job to its completion. Soft real-time systems areless restrictive that the critical real-time task get the priority over others and retainthat priority until it completes. Generally they are not used as industrial controller and robots. They are used in several areas like multimedia and even also

supported by various modern operating systems. And required more restrictedadvance operating system features then hard real-time system.

Generally preemptive priority based scheduling is used in RTOS to schedulevarious tasks. In the case of hard real-time system is submitted to the systemwith a statement amount of time in which it will complete. The scheduler either submit the process with the guarantee that the process will complete within thedefined time constraint or it will reject from the submission as impossible. On theother hand, soft real-time systems use priority based scheduling scheme. In softreal-time system a critical real time task get highest priority over other tasks.

In hard real-time system secondary storage either limited or missing. Data arestored in short term memory on in ROM. Since advance operation systemfeatures are missing, so virtual memory is almost never found. Whereas soft real-time systems require advance operating system features. There are two type of management. In first type memory is divided into fixed size of memory blocks.The scheduler fetches the new job in the free block. In second type dynamicswapping of code in and out scheme is used. To fulfill that scheme variousschemes –swapping, demand paging, MFT, MVT are used.

The applications of RTOS are very wide. Many applications require real-timefunctionality, like weapon systems, embedded industries, robots and many more.Even modern operating systems also support real-time functionality like, supportof multimedia, scheduling of task. RTOS functionality is also supported by Java.

Jbed package is used to provide real-time virtual machine of embedded systemsand on internet under Java platform.

BIBLIOGRAPHYBIBLIOGRAPHY

Operating System Concepts –Silberschatz, Galvin, Gagne

www.netrino.com

http://people.msoe.edu/~sebern/courses/cs384/papers98/verber.pd

f

A Survey of Real-time Operating Systems [ Internet ]

Address:http://www.ece.stevens-tech.edu/~ymeng/courses/embedded_systems/papers/rtos_paper.pdf

9/10By: Mukul Garg

http://www.netrino.com/

http://people.msoe.edu/~sebern/courses/cs384/papers98/verber.pdf


http://www.ece.stevens-tech.edu/~ymeng/courses/embedded_systems/papers/rtos_paper.pdf


http://www.netrino.com/








10/10By: Mukul Garg

rtos document

Documents