COURSE/TERM PAPER

Topic: Embedded Systems Name: Nyalala Innocent Odira College: 信息科学技术学院 Major: 计算机应用技术 Number: 2013114033 Teacher’s Name: 2014年1月 5日 | 南京农业大学教务处制 |
Embedded system is a specialized computer system that is part of a larger system or machine. Typically, an embedded system is housed on a single microprocessor board with the programs stored in ROM. Virtually all appliances that have a digital interface like watches, microwaves, VCRs, cars etc., utilize embedded systems. Some embedded systems include an operating sys-tem, but many are so specialized that the entire logic can be implemented as a single program. The term paper would elaborate the history of embedded systems, the generations of its development, the components of embedded systems, its design issues and the programming languages that are used to build it. Then this paper would also include its current state of art, its uses, its current applications, the problems that have occurred in designing such kind of systems, also the steps taken to solve such problems and its future prospects.

1. INTRODUCTION
These are the days when the term like embedded is increasingly becoming more and more popular in the world. We are flooded with embedded systems that seem to be everywhere. Now the question is what basically embedded systems are. We can define an embedded system as a microprocessor based system that does not look like a computer. Or we can say that it is a combination of computer hardware and software, and perhaps additional mechanical or other parts, designed to perform a dedicated function. In some cases, embedded systems are part of a larger system or product, as is the case of an antilock braking system in a car.
Embedded systems include a variety of hardware and software components, which perform specific functions in host systems, for example, satellites, washing machines, robots, hand-held telephones and automobiles. Modem, hard drive, floppy drive, and sound card each of which is an embedded system. Each of these devices contains a processor and software and is designed to perform a specific function. For example, the modem is designed to send and receive digital data over an analog telephone line. That's it. And all of the other devices can be summarized in a single sentence as well. If an embedded system is designed well, the existence of the processor and software could be completely unnoticed by a user of the device. Such is the case for a microwave oven, VCR, or alarm clock. In some cases, it would even be possible to build an equivalent device that does not contain the processor and software.

2. HISTORY
Given the definition of embedded systems earlier, the first such systems could not possibly have appeared before 1971. That was the year Intel introduced the world's first microprocessor. This chip, the 4004, was de-signed for use in a line of business calculators produced by the Japanese company Busicom. In 1969, Busicom asked Intel to design a set of custom integrated circuits-one for each of their new calculator models. The 4004 were Intel's response. Rather than design custom hardware for each calculator, Intel proposed a general-purpose circuit that could be used throughout the entire line of calculators. This general purpose processor was designed to read and execute a set of instructions software stored in an external memory chip. Intel's idea was that the software would give each calculator its unique set of features. The microprocessor was an overnight success, and its use increased steadily over the next decade. Early embedded applications included unmanned space probes, computerized traffic lights, and aircraft flight control systems. In the 1980s, embedded systems quietly rode the waves of the microcomputer age and brought microprocessors into every part of our personal and professional lives.
Many of the electronic devices in our kitchens (bread machines, food processors, and microwave ovens), living rooms (televisions, stereos, and remote controls), and workplaces (fax machines, pagers, laser printers, cash registers, and credit card readers) are embedded systems. It seems inevitable that the number of embedded systems will continue to increase rapidly. Already there are promising new embedded devices that have enormous market potential: light switches and thermostats that can be controlled by a central computer, intelligent airbag systems that don't inflate when children or small adults are present, palm-sized electronic organizers and personal digital assistants (PDAs), digital cameras, and dashboard navigation systems. Clearly, individuals who possess the skills and desire to design the next generation of embedded systems will be in demand for quite some time. Embedded systems really took off in 1992, when Ampro, RTD, and other manufacturers founded the PC/104 Consortium. The group established a format for Intel microprocessors based on a motherboard approximately four inches square, and just under an inch high. The boards were stack-able, allowing a very powerful computer to be assembled in a box. The PC/104 was initially targeted at military and medical markets, where it became widely used and respect-ed. When the processor power increased enough to handle multimedia applications, PC/104-based kiosks became possible, and eventually common. The first recognizably modern embedded system was the Apollo Guidance Computer, developed by Charles Draper and the MIT Instrumentation Laboratory. Each flight to the moon had two. At the project's inception, the Apollo guidance computer was considered the riskiest item in the Apollo project. The first mass produced embedded system was the guidance computer for the minuteman missile. It also used integrated circuits, and was the first volume user of them. Without this program, integrated circuits might never have reached a usable price-point. The crucial design features of the minuteman computer were that its guidance algorithm could be reprogrammed later in the program, to make the missile more accurate.

3. CURRENT DEFINITION
A specialized computer system that is part of a larger system or machine. Typically, an embedded system is housed on a single microprocessor board with the programs stored in ROM.
Virtually all appliances that have a digital Interface like watches, microwaves, VCRs, cars utilize embedded systems. Some embedded systems include an operating system, but many are so specialized that the entire logic can be implemented as a single program.
4. ATTRIBUTES OF AN EMBEDDED SYSTEM
As embedded systems started progressing, they started becoming more and more complex. Additionally, new attributes that got added to these systems were smart and intelligent. Not only were the embedded devices able to do their jobs but also were able to do them smartly. These attributes can be defined as;
4.1 Computational Power
These devices have some amount of computing power. Avery simple 8-bit controller or a high-end 64-bit microprocessor could provide this computation power.
4.2 Memory
The next requirement is memory. These devices possess some amount of memory that can be used by the processor and also some to remember user data and preferences.
4.3 Real time
All the devices have to respond to user/environmental in-puts within a specified period of time.
4.4 Communication
The device must be able to receive inputs given by other devices in the environment, process it and provide some solid output to the other devices or users.
4.5 Dynamic decisions
The system should be able to change its next course of activity based on the change of input from its sensors or surroundings.

5. CHALLENGES FOR AN EMBEDDED SYSTEM
The embedded processors are getting more and more powerful. It is not uncommon to find embedded systems withpowerful processors, like mobile (GSM/GPRS) handsets, high-speed routers, bridges etc. Programming for the designing of such complex devices offers unique challenges not found in PC/workstations based applications. Some of them are listed below:
5.1 Limited Operating System Support For Programming
Application programs for PCs/workstations are launched from the operating system. The tasks like memory management, scheduling, hardware abstractions and input/output from/to peripherals are delegated to OS. All these tasks are handled by the operating system in a PC environment. In embedded systems, the OS is part of application code and it closely co-ordinates with the OS to support a majority of the features that a desktop OS may provide.
5.2 Limited Secondary Memory Many embedded systems do not boot from a hard disk. They depend on other types of non-volatile memory like ROM, FLASH memory, instead of secondary memory de-vices. As systems with 16 MB flash are considered premium, therefore our code and data sizes must be small.
5.3 Limited Random Access Memory
Since embedded systems inherently operate with restriction on resources (limited resource could be provided), we usually don’t have the concept of swapping and virtual memory etc., in embedded systems. Therefore, while programming for embedded systems, we must be very careful about the memory leaks because these programs tend to run forever, and even a single byte leak in some path of execution will definitely bring the system to a grinding halt at a later point of time.
5.4 Limited Processing Time
We cannot afford to have a powerful processor for an embedded system because of obvious cost considerations. Therefore we may have to work with some microcontrollerswith less powerful configurations. So, the code writtenmust be efficient. We have to choose appropriate algorithms and cannot choose an algorithm with high computing requirements unnecessarily.
5.5 Interaction with hardware
This factor singularly differentiates a normal application programming from embedded programming. An application programmer using the most modern operating system can develop software, by remained unaware of the underlying hardware. But, an embedded programmer usually cannot afford this level of hardware independence since its code directly interacts with the underlying hardware. Embedded programmers usually have to work with real time operating systems that generally cannot provide such a high level of abstraction over hardware due to space and time restrictions.
5.6 Absence of standard Input/output devices
A PC has standard I/O devices like keyboard, mouse and a display that can be used to display what’s happening in-side our program. But many of the embedded devices don’t have such I/O devices. So, a programmer has no direct way of knowing what is happening within the system. This seriously limits the amount of debugging possible on an embedded system.
6. FUNDAMENTAL COMPONENTS OF EMBEDDED SYSTEMS:
Usually all embedded systems have a lot in common in terms of their components and their requirements. Some of these requirements and components are:
6.1 Computational/ Processing Power
This is one of the primary requirements of an embedded system. All systems take input from the user or the environment. The processing, however, can be done using microprocessor or a hydraulic circuit or a simple electrical/electronic circuit. This processing power is required to translate the request from the user, changes in the environment to the output as desired by the end user. This processing logic that used to be “hardwired” in a chip or other electrical circuits grew up exponentially and is so complex nowadays that much functionality is simply unimaginable without software. The usual practice is to hardwire ‘mature’ features in hardware and use software to implement developing features. An embedded system can also take inputs from the environment e.g., a refrigerator or an air conditioner has various functionalities like defrost, air circulation, temperature control etc. Some advanced refrigerators may have sensors to deodorize and detect inactivity. To compute and regulate the various parameters a sys-tem may require various levels of computing power. The microcontroller can be chosen based on the required level of computing power.
6.2 Memory
Memory is a very precious resource and is always found wanting in many embedded systems. As due to intense price wars, every resource must be handled with extreme care. In many systems, some space has to be allocated for future expansions. We cannot afford expansion slots as in PC for embedded system due to embedded-hardware de-sign constraints. So, memory should be handled very care-fully. Algorithms that use a huge amount of memory or copying of huge data structures are ignored unless it is an absolute necessity. Many embedded systems do not carry hard disk or floppy disk drives with them. The usage of secondary storage is not possible in most embedded systems. So these systems usually have some ROM and nonvolatile RAM where the code and user preferences are stored. Some of the programs do not terminate and tend to run forever. In case of some special type of systems, when emergency strikes or when some irrecoverable error occurs, embedded systems implement watchdog timers which just reset the system.
6.3 Real time
We can define a system as a collection of subsystems or components that respond to the inputs from the user or the environment or from itself (e.g., timers). Typically, there is a time lapse between the time at which the input is given and the time at which the system responds. In any system, it is quite natural to expect some response within a specific time interval. But, there are systems where, very strict (not necessarily short) deadlines have to be met. These systems are called real time systems. These systems are characterized as,
“A late answer is a wrong answer”. Real time systems can be classified as;
6.3.1 Hard Real time Systems
A real time system where missing a deadline could cause drastic results that could lead to loss of life/property. For example, aircrafts, nuclear reactors etc.
6.3.2 Soft Real time Systems
A real time system where a few missed deadlines may not cause any significant inconvenience to the user. For example, televisions, DVD player or music system, multimedia streaming over Internet (where loss of some packets can be afforded).The real time systems can also be classified as fast andslow systems based on the time deadlines they operatewith.Closely associated with the concept of real time is the concept of determinism. This is also a very important concept that differentiates real time programming from normal application programming. A real time system is the one that behaves predictably, as it responds within a particular amount of time. The time interval between the instant at which the input occurred to the time instance at which output occurs should be ‘deterministic’ or predictable. It just requires that the system should always respond within a known period of time.
6.4 Communication Elements
Embedded devices and appliances can no longer remain as islands of information storage. They cannot remain isolated; rather they need to communicate with each other to perform any operation that is desired by the user. These communications could be done with some wireless networking protocols like Bluetooth, Wireless LAN etc. The communication element adds “intelligence” to simple embedded real time system. The other important parameters that define an embedded system are;
6.4.1 Cost
Cost is the major driving factor behind many embedded systems. This requires the designer to be extremely conscious about memory, peripherals etc. This factor plays an important role in high volume products.
6.4.2 Reliability
Some products require 99.999% proper processing. But some doesn’t like a bread piece in a toaster. Reliability may require the designer to opt for some level of redundancy.
6.4.3 Lifetime
Products that have a longer lifetime must be built with robust and proven components.
6.4.4 Power consumption
This factor has become an important area of research in itself. With growing number of mobile instruments, power consumption has become a major concern. The design of mobile devices is such that the power consumption is reduced to the minimum. Some of the popular tactics used include shutting down those peripherals which are not immediately required. These tactics are highly dependent on software. The programmer for mobile devices is becoming increasingly aware of the power saving features in their programming platform.
7. APPLICATIONS OF EMBEDDED SYSTEMS
Embedded systems are the applications that fuel some of the microprocessors that play a hidden but crucial role in our everyday lives. These are the tiny, quick, and smart microprocessors that live inside printers, answering machines, elevators, cars, cash machines, refrigerators, thermostats, wrist watches, and even toasters. Embedded systems are on the cutting edge of consumer electronics, poised to revolutionize various technologies by making them "smarter." Embedded System Applications describes the latest techniques for embedded system design in a variety of applications. This also includes some of the latest software tools for embedded system design. Applications of embedded sys-tem design in satellites, radio astronomy, space and control systems. Some of the other examples of embedded systems are as follows: 1. Automatic teller machines
2. Computer printers
3. Disk drives
4. Cellular telephones and telephone switches.
5. Inertial guidance systems for aircraft and missiles.
6. Medical equipment’s
7. Video game consoles
8. Industrial machinery use programmable logic controllers to handle automation and monitoring.
9. Engine control computers and antilock brake controllers for automobiles
10. Wristwatches
11. Household appliances, including microwaveovens, air conditioners, iron, washing
Machines, and television sets
12. Home automation products, like thermostats, sprinkler, and security monitoring systems
13. Network equipment, including routers and firewalls
14. Traffic control (e.g. intelligent traffic lights)
15. Music Systems
16. Card Reader
Some of its examples would be elaborated in more detail as follows;
7.1 Music Systems
Today’s advanced music systems are very complex embedded devices. They contain a variety of features such as the ability to play various types of media like the magnetic tape (cassettes), audio/video CDs, DVDs, etc. They also have the support to preset different types of music like jazz, rock, classical, vocal, etc. and the environment (hall, theatre, open-air, etc.). These features are not hardwired in chips but are usually taken care of by the software that is with these systems. The processors are typically 8-bit microprocessors for handling user inputs and display. They have MPEG de-coders for decoding the input stream for various supported media. The RAM for these kinds of systems can vary a lot from 64KB to a few MB depending on how complex the system is. For the real-time feature, the media should be read, decoded and the stream must be sent to the speakers/video output at a predefined rate. This system needs to interact with its components as well as other devices in real-time so that the desired functionality is achieved like playing your favorite music with the help of Bluetooth.
7.2 Card Reader
This is one of the systems that are often encountered in buildings that incorporate a security system. A person who wants to gain entry to the systems must flash his/her magnetic card in front of the reader. The reader then validates the card and may provide or deny access based on the privileges given to the card. The system does not have very complex software. On flashing of the card as detected by the magnetic sensor, the card identifier is looked upon in the access control list. If the card does have the access permit then the output on the unit flashes and the door is unlocked for entry. Or, the system can emit a sound or display that the access is not permitted. The unit should just look up the access table and respond to the user accordingly. However, this should happen sufficiently fast, typically in less than a second. We cannot afford to have a few seconds lapse because, the user may assume that his access was not permitted or the system is dysfunctional. The lists can be stored in a central server where the look up can be done. In this case, the authentication unit may not require storing of all the lists in its memory. Or, it can store the list only for the location for which it controls the access. This is left entirely to the programming style of the de-signer of the system. The memory required for this system will depend on the method opted for its design. These units are connected with each other.
7.3 Washing Machine
The main purpose of a washing machine is just to wash cloths. But the modern world has extended it to include extra functionalities and gives more control thereby optimizing the actual process of washing clothes. Nowadays, washing machines come complete with sensors, which maintain optimum water temperature, cloth dependent spin-speed, number of spins, etc. They take care of filling water, heating it to particular temperature, mixing the optimum amount of detergent, soaking the clothes in water for just the right time, the soft tumble for extracting dirt and removing stains, and excessive detergent from clothes, and finally the spin-dry. All this happens with the minimum user interventions. The user may just have to select what kind of clothes is being put inside the machine. All these functionalities are handled by a small microprocessor. Since microprocessor cannot work in isolation, it needs inputs from sensors and other controlling devices so as to feel what is going around and then decides what actions are needed to be performed, which parts of the system have to run and in which order.
7.4 Digital Watch
At the end of the evolutionary path that began with sundials, water clocks, and hourglasses is the digital watch. Among its many features are the presentation of the date and time (usually to the nearest second), the measurement of the length of an event to the nearest hundredth of a second, and the generation of an annoying little sound at the beginning of each hour. As it turns out, these are very simple tasks that do not require very much processing power or memory. In fact, the only reason to employ a processor at all is to support a range of models and features from a single hardware design. The typical digital watch contains a simple, inexpensive 8- bit processor. Because such small processors cannot address very much memory, this type of processor usually contains its own on-chip ROM. And, if there are sufficient registers available, this application may not require any RAM at all. In fact, all of the electronics-processor, memory, counters and real-time clocks-are likely to be stored in a single chip. The only other hardware elements of the watch are the in-puts (buttons) and outputs (LCD and speaker).
The watch designer's goal is to create a reasonably reliable product that has an extraordinarily low production cost. If, after production, some watches are found to keep more reliable time than most, they can be sold under a brand name with a higher markup. Otherwise, a profit can still be made by selling the watch through a discount sales channel. Forlower-cost versions, the stopwatch buttons or speaker could be eliminated. This would limit the functionality of thewatch but might not even require any software changes. And, of course, the cost of all this development effort may be fairly high, since it will be amortized over hundreds of thousands or even millions of watch sales.
7.5 Video Game Player
When you pull the Nintendo-64 or Sony PlayStation out from your entertainment center, you are preparing to use an embedded system. In some cases, these machines are more powerful than the comparable generation of personal computers. Yet video game players for the home market are relatively inexpensive compared to personal computers. It is the competing requirements of high processing power and low production cost that keep video game designers awake at night (and their children well fed).The companies that produce video game players don't usually care how much it costs to develop the system, so long as the production costs of the resulting product are low typically around a hundred dollars. They might even encourage their engineers to design custom processors at a development cost of hundreds of thousands of dollars each. So, although there might be a 64-bit processor inside your video game player, it is not necessarily the same type of processor that would be found in a 64-bit personal computer. In all likelihood, the processor is highly specialized for the demands of the video games it is intended to play. Because production cost is so crucial in the home videogame market, the designers also use tricks to shift the costs around. For example, one common tactic is to move as much of the memory and other peripheral electronics as possible off of the main circuit board and onto the game cartridges. This helps to reduce the cost of the game player, but increases the price of each and every game. So, while the system might have a powerful 64-bit processor, it might have only a few megabytes of memory on the main circuit board. This is just enough memory to bootstrap the ma-chine to a state from which it can access additional memory on the game cartridge.

8. BENEFITS OF EMBEDDED SYSTEMS
Taking reference of the above examples, we can well imagine how much such kinds of systems have served humanity. Whether these benefits are in concerned with security purposes or with human’s comforts, in fact these intelligent systems helped humanity in every phase of life. They have helped man in their progress by developing the new technologies. Embedded microprocessors enable firms to compete on product and service innovation, by adding product and service features that customer’s value, but which would be largely impossible without this technology. According to market researchers, consumers love electronic equipment that can do "smart" things like transmit instructions to other devices wirelessly via infrared signals; be programmed to operate automatically; and connect to super-technologies, such as satellites, to bring remote power into their own hands. Such systems have made their life easy and comfortable. Thus in short such systems have facilitated, by fulfilling the needs of a man or giving him luxuries.

9. DESIGN OF EMBEDDED SYSTEMS
Design of embedded software, precise specification of the software that has to be built, including
1. Assumptions on the environment and on other components in the system.
2. Requirements on the implementation such as available hardware, memory usage, safety, error handling and use of energy.
3. Analysis of real-time behavior should be done to ensure that the deadlines are met on time. This requires proper allocation of processes to processor, scheduling of the tasks and assignment of priorities.
4. The selection of protocols for establishing communication between components, and the analysis to check the correctness and performance of the selected protocols.
5. The use of advanced methods for the designs should be ensured to achieve the required level of correctness and reliability.

10. REASONS FOR THE DIFFICULTY IN DESIGNING EMBEDDED SYSTEMS
Several reasons that development of embedded systems is more difficult than development of any other software are as follows:
1. Complexity. The designing of embedded system is more complex than any other software.
2. Testing. There are more failure cases; therefore correctness is often more important.
3. Predictability. The performance of a system must be predictable in order for people to have confidence in it. If the performance is variable, then one is never sure that the system will meet its resource requirements on any given execution.
4. Specification. The specifications of an embedded system must be more detailed.
5. Domain Knowledge. The programmers must have more domain knowledge than usual.
6. Fault tolerance. Embedded systems frequently require effective fault tolerance, so that when one or two things go wrong the system is able to at least partially recover. Failure of embedded systems of-ten may have serious consequences (loss of lives, huge financial losses), so correctness and reliability are of vital importance.

11. LANGUAGES FOR PROGRAMMING EMBEDDED SYSTEMS
Assembly language was the pioneer for programming embedded systems till recently. Nowadays there are many more languages to program these systems. Some of the languages are C, C++, Ada, Forth, and Java together with its new enhancement J2ME. The presence of tools to model the software in UML, SDL is sufficient to indicate the maturity of embedded software programming. The majority of software for embedded systems is still done in C language. Recent survey indicates that approximately 45% of the embedded software is still being done in C language. C++ is also increasing its presence in embedded systems. As C++ is based on C language, thus providing programmer the object oriented methodologies to reap the benefits of such an approach. C is very close to assembly programming and it allows very easy access to underlying hardware. A huge number of high quality compilers and debugging tools are available for the C language. Though C++ is theoretically more efficient than C, but some of its compilers have bugs due to the huge size of the language. These compilers may cause a buggy execution. C language can definitely claim to have more mature compilers C++. Now in order to avail the extra benefits of C++ and plus to avoid buggy execution, expertsare doing efforts to identify a subset of C++ that can be used in embedded systems and this subset is called Embedded C++[1].The software tools (compilers, assemblers and debugger)used to develop an embedded system can come from several sources:
1. Software companies that specialize in the embedded market.
2. Ported from the GNU software development tools.
3. Sometimes, development tools for a personal computer can be used if the embedded processor is a close relative to a common PC processor.

12. FUTURE PROSPECTS
It is unavoidable that computer will continue to become cheaper, smaller and more powerful, and that eventually they will be inexpensive enough to put in nearly every product. In addition, nearly all computers equipped products will have some kind of access to either local networks, or the Internet. Over the next decade, many common household items will be given embedded systems, reinventing them, and changing them for forever. Like desktop publishing, and later the Internet, embedded systems are a technology that will fundamentally, and permanently, change the way advertising and marketing works. It will also permanently change the kind of products that are made, and how they are made. The development of intelligent products, and intelligent product marketing, made possible by embedded systems, where these machines exist for the convenience of people. The rise of embedded systems marks a new phase in indus-trialization.No doubt, the field of embedded system is gettingmore and more challenging, and issues in development of embedded software are becoming very attracting to a wide number of researchers both in industry and academia. In fact, lots of effort is being done in the development of embedded systems and many researchers are still working on it to make the systems more intelligent and smarter. With the fast pace of technological progress, that future may be right around the corner.

CONCLUSION
We have looked into the details of the embedded systems; we have discussed its characteristics, its components, the challenges programmer faces while designing such systems, its practical implementations, its importance in daily life and its future prospects. In short, embedded systems play an important role in our daily life work. This technology has made our lives easier and in few decades, it would probably change the outlook of this world.

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