EMBEDDED SYSTEM

                    EMBEDDED  SYSTEM

                                                    By,

                              D.GOWRI  
                                          II B.Tech , E.C.E.,  
                                             e-mail :gowri_btech2005 @ yahoo.co.in

                                                      &
                                                 Y.SUJALA                              II B.Tech ,E.C.E.,

 




            MEKAPATI  RAJA  MOHAN REDDY
INSTITUTE  OF  TECHNOLOGY  AND  SCIENCE
                             MeRITS,
                             UDAYAGIRI,
                             NELLORE(dt).





 ABSTRACT:
                                   
                              This paper attempts to investigate the approach of embedded                                       systems. The embedded system is a combination of computer                                hardware, software and perhaps additional mechanical or other
                              parts, designed to perform a specific function within a given time                                    frame.





















 KEYWORDS:
                          Design of embedded systems, embedded  software   architectures, user interfaces.
 INTRODUCTION:
                        An embedded system is a special-purpose computer system built into a   larger device .An embedded-system is typically required to meet very different requirements than a general-purpose personal computer Two major areas of differences are cost and power consumption. Since many embedded systems are produced in the tens of thousands to millions of units range, reducing cost is a major concern. Embedded systems often use a (relatively) slow processor and small memory size to minimize costs.
 •    Some of the attributes of the coming era:
1. The number of smart devices ( i.e., products with embedded operating                                                                                                                     systems inside )  will grow exponentially,  reaching numbers  in the billions.
2. The choice of CPU will be more a matter of cost than technology or a                            architecture
3. Nearly all devices will have connectivity, whether wired or wireless.
4. Most devices will have the ability to be upgraded or repaired remotely,                                                            by downloading new firmware or software.
                      Most devices will have specific rather than general-purpose functionality,     so their users application software will be defined by the manufactures (rather than loaded by their).
                     This needs to, “minimize cost and maximize specialization”creates the opportunity for embedded systems.
 Paper  Identification  Number  : SS-2.5
           This peer reviewed paper has been published by the Pentagram Research         Centre  (p)  limited. Responsibility of contents of this paper rests upon the authors and not upon pentagram research center  (p)  limited. Copies can be obtained from the company for a cost.
             Embedded systems are becoming all pervasive. Every microwave has one. A cellular hand phone has two. A luxury Mercedes car has around 40. The latest Boeing 777-302,will have tens of dozens-we’re  talking about the ubiquitous microprocessor chips and their associated peripheral devices.
                             To cite other examples, embedded software allows your washing machine to choose speed according to the type of cloth, gives thinking power to the microwave, acts like a music conductor in the car engine and pushes rocket launchers into space    
                              The embedded system generally comprises topics like real time embedded digital signal processing, microprocessor architecture programming concepts; Real-time Operating System (QXN,   RT  Linux, V x Works); Micro controllers; Embedded Systems  Programming Data Communication Networking, C concepts and linux among others.
  START UP:
                     All embedded systems have start-up code. Usually it disables interrupts, sets of up the electronics, tests the computer (RAM, CPU and software), and then starts the application code. Many embedded systems recover from short-term power failures by skipping the self-tests if the software can prove they were done recently. Restart times under a tenth of a second are common.
                            “Embedded systems’ has come to mean “micro-controller programming”. With the increasing proliferation of embedded systems, and advances in hardware and software technologies and the blurring of the boundary between them we need a more meaning-ful glimpse into this area. “Embedded systems’ addresses this need and brings out the issues in building modern-embedded systems.
 DESIGN OF EMBEDDED SYSTEMS
                        The electronics usually  uses  either a microprocessor or a microcontroller some large are old systems use general-purpose mainframe computers are mini computers. Embedded systems design is getting complex, requiring intimate knowledge of both the hardware and software worlds.  Cramming all those chips in a square centimetre of silicon real estate is more an art then a science. Getting the software to work with limited memory is often a struggle. Designers embedded systems strive to  improve performance, reliability and cost effectiveness. Hardware and software choices are simultaneously considered. This is called co-design.        
The goal is to produce an efficient implementation that satisfies-performance and cost requirements on the design the entire system on a chip-the SOC approach. Information appliances can be fabricated from custom SOC silicon .This has been successful in designing cellular hand phones where the high volume usually dictate this design strategy.
        CHARACTERISTICS :  
              Two major areas of differences are cost and power consumption . Since many       embedded systems are produced in the tens of thousands to millions of units range, reducing cost is a major concern. Embedded systems often use a (relatively) slow processor and small memory size to minimize costs.
                        The slowness is not just clock speed. The whole architecture of the computer is often intentionally simplified to lower costs.
For example embedded systems often use peripherals controlled by synchronous serial Interfaces, Which are ten to hundreds of times slower than comparable peripheral used in PCs.  Programs on an embedded   systems often must run with real time constrains with limited hard ware resources:
                    Often there is no disk drive, operating system , keyboard or screen. A flash drive may replace rotating media and a small keypad and LCD screen may be used instead of a PCs keyboard and screen.
                           Firmware is the name for software that is embedded in hardware devices, e.g. in one or more ROM memory  IC chips .
       PLATFORM:
                             There are many different CPU architecture used in embedded designs.
This in contrast to the disk top computer marke-t, which as of this writing (2003) is to
limited just a few competing architectures , chieply intel’s  x86,and the apple/Motorola/IBM power PC, used in the  apple macintosh.
                         One common configuration for embedded system is the system on a chip, an application specific integrated circuit, for which the CPU was purchased as intellectual property  to add to IC’s design.

 TOOLS:
                  Like a typical computer programmer, embedded system, designers use compiler, assembler and debbuger to develop an embedded system.
Those software tools can come from several sources:
 Soft-ware companies that specialize in the embedded market. Ported  from the GNU software development tolls. Some times, development tools for a personal computer can be used if the embedded process is a close relative to a common PC processors .                   Embedded system designers also use a few software tools rarely used by typical computer  programmers.
                    Some designers keep a utility  program to turn data files into codes, so that they can include any kind of data in a program.Most designers also have utility programs  to add a check sum or CRC  to a program, so it can check its program data before executing  it.
  OPERATING SYSTEM:
                          They often have no operating system or a specialized embedded operating  system (often real time operating system), or the programmer is assigned   to part one of these to the new system .
  EMBEDDED SOFTWARE ARCHITECTURES;
                          There are severally basical different types of software architectures in common use.
 THE CONTROL LOOP:
                           In this design, the software simply has a loop. The loop calls subroutines. Each subroutine manages apart of the hardware or software. Interrupts  generally set  flags, or update counters that are read by the rest of the software.
                          A simple API disables  and enables interrupts. Done right, it handles nested calls in Nested subroutines, and restores the preceding interrupt state in the outer most enable. This is one of the simplest methods of creating an exokernel.
Typically, there’s some sort of subroutine in the loop to manage a list of software timers, using a periodic real time interrupt.
                           When a timer expire, an associated subroutine is run, or flag is set .  Any expected hardware event should be backed-up with a software timer . Hardware events fail about ones in a  trillion times.                        
                           That’s about once a year with modern hardware. With a million mass-produced devices, living out a software timer is a business disaster.
                            State machines are implemented with a function-pointer per state- machine (in C++, C or assembly any way). A change of state stores a different function into the pointer. The function pointer is executed every time the loop runs.
                             Many designers recommend reading   each IO device once per loop, and storing the result so the logic acts on consistent values.
                            Any designers prefer to design their  state machines to check only one are two things per states. Usually this is a hardware event, and a  software timer .
Designers recommand the hierarchical state machines  should run the lower-level state  Machine before the higher,  so the higher run with accurate information.
                            Complex function like internal combustion control are often handle with multi-dimensional tables.
                             Instead of complex calculations the code looks up the values. The software can interpolate between entries, to keep the table small and cheap.                    One major weakness of this system is that it does not guarantee a time to respond to any particular hardware event. Careful  coding can easily assure that nothing disables interrupts for long.
                             Thus interrupt code can run at vary precise timings.Another major weakness of this system is that it can become complex to add  few features. Algorithms that take along time to run must be carefully broken down so only a little piece gets done each time through the main loop.
                            This system’s strength is it’s simplicity, and on small pieces  of software the loop is usually so fast that nobody cares that is not predictable.
                            Another advantage is that system guarantees that a software will run. There is no mysterious operating system to blame for bad behaviour.


 USER INTERFACES:

                              User interfaces  for embedded systems vary wildly, and thus deserve some special comment. Designers recommend testing the user interface for usability at the earliest possible instant.                        
                              Exactly one person should approve the user interface ideally, this should be a   customer, the major distributor or someone directly responsible for selling the system. The decision maker should be  able to decide. The problem is that a committee  will never make-up its mind, and neither will some people.  Not doing in this causes avoidable, expensive delays. A usability test is more important then any number of opinions. A touch-screen or screen-edge buttons also minimize that types of user actions. Another basic trick is to minimize and simplify the type output.
                              Designs should consider using  a status light for each interface plug, or failure condition ,to tell what failed. A cheap variation is to have two light bars with a printed matrix of errors that they select-the user can glue on the labels for the languages that she speaks.
                           For example, Boeing’s standard test interface is a button and some lights.                           When you press the button all the lights turn on. When you release the button the lights with failures say on. The labels  are in basic english. For another example, look  at a small computer printer. You might have one next to your computer. Notice that the lights are labeled with stick-on the labels that can be printed in any language. Really look at it.
                            Designers use colors. Red means the user can get hurt-think of blood.
Yellow means some thing might be wrong. Green means everything’s OK. Another essential trick is to make any modes absolutely clear on the user’s display.
                             An interface has modes, they must be reversible in an obvious way.
Most designers prefer the display to respond to the user. The display should change immediately after a user action. If the machine is going to do any thing, it should  start within 7 seconds, or give progress reports. If a design needs a screen, many designers use plain text.


      APPLICATIONS OF  EMBEDDED SYSTEM:
• . Automatic Teller Machine (ATM).
• . Cellular telephones and telephone switches.
• . Computer network Equipment , including router and fire wall.………
• . Computer Printer .
• . Disk drive .
• . Engine controller and antilock break controller for automobiles.
• . Home auto machine products, like thermostat sprinkler, and security monitoring        .     .     systems.
• . Handheld  Calculator.
• . Household appliance, including. Microwave oven ,washing machine ,television sets .                   .     DVD  players/recorders.
• . Inertial guidance system for air-craft and missile.
• . Medical Equipment.
• . Multi function Wristwatches.
• . Personal digital assistants.
• . Programmable logic control for industrial automation and monitoring.
• . Video game console.

 CONCLUSION:
                   In this paper  we had tried to cover the fundamental principles of embedded systems used in modern digital instruments. In modern world the major problem with present desktop system is that they are very bulky   in size to they cause severe problem in their decomposition. But as the embedded system does same task with smaller size made then vary useful for electronic instruments and many others. So it’s the most crucial thing which will become the heart of every electronic device in feature.

 REFERENCES:
1. http://www.bambooweb.com/articles/e/m/embedded system.html
2. http://www.oranetech.com/