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1.Introduction

An embedded system is a computersystem with a dedicated function within a larger mechanical

or electrical system, often with real-time computing constraints. It is embedded as part of a

complete device often including hardware and mechanical parts. By contrast, a general-purpose

computer, such as apersonal computer (PC), is designed to be flexible and to meet a wide rangeof end-user needs. Embedded systems control many devices in common use today.

Embedded systems contain processing cores that are either microcontrollers, or digitalsignal processors (DSP).

A processor is an important unit in the embedded system hardware. It is the heart of theembedded system.

The key characteristic, however, is being dedicated to handle a particular task. Since the

embedded system is dedicated to specific tasks, design engineers can optimize it to reduce the

size and cost of the product and increase the reliability and performance. Some embedded

systems are mass-produced, benefiting fromeconomies of scale.

Physically, embedded systems range from portable devices such as digital watches and

MP3 players, to large stationary installations like traffic lights, factory controllers, and largelycomplex systems likehybrid vehicles,MRI,and avionics.Complexity varies from low, with a

singlemicrocontroller chip, to very high with multiple units,peripherals and networks mounted

inside a largechassis or enclosure.

Embedded systems are commonly found in consumer, cooking, industrial, automotive,

medical, commercial and military applications.

Telecommunications systems employ numerous embedded systems from telephone

switches for the network tomobile phones at the end-user. Computer networking uses dedicatedrouters andnetwork bridges to route data.

Consumer electronics include personal digital assistants (PDAs), mp3 players, mobilephones, videogame consoles,digital cameras, DVDplayers, GPS receivers, andprinters.Many

household appliances, such as microwave ovens, washing machines and dishwashers, include

embedded systems to provide flexibility, efficiency and features. AdvancedHVAC systems usenetworkedthermostats to more accurately and efficiently control temperature that can change by

time of day andseason.Home automation uses wired- and wireless-networking that can be used
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to control lights, climate, security, audio/visual, surveillance, etc., all of which use embedded

devices for sensing and controlling.

Transportation systems from flight to automobiles increasingly use embedded systems.

New airplanes contain advanced avionics such as inertial guidance systems and GPS receivers

that also have considerable safety requirements. Various electric motors brushlessDCmotors,induction motors and DC motors use electric/electronic motor controllers. Automobiles,

electric vehicles,andhybrid vehicles increasingly use embedded systems to maximize efficiency

and reduce pollution. Other automotive safety systems includeanti-lock braking system (ABS),Electronic Stability Control (ESC/ESP),traction control (TCS) and automaticfour-wheel drive.

Medical equipment uses embedded systems for vital signs monitoring, electronicstethoscopes for amplifying sounds, and various medical imaging (PET,SPECT,CT,MRI)for

non-invasive internal inspections. Embedded systems within medical equipment are often

powered by industrial computers.

Embedded systems are used in transportation, fire safety, safety and security, medicalapplications and life critical systems, as these systems can be isolated from hacking and thus, be

more reliable. For fire safety, the systems can be designed to have greater ability to handle highertemperatures and continue to operate. In dealing with security, the embedded systems can be

self-sufficient and be able to deal with cut electrical and communication systems.

A new class of miniature wireless devices calledmotes are quickly gaining popularity as

the field of wireless sensor networking is increasing. Wireless sensor networking, WSN,makes

use of miniaturization made possible by advanced IC design to couple full wireless subsystemsto sophisticated sensors, enabling people and companies to measure a myriad of things in the

physical world and act on this information through IT monitoring and control systems. These

motes are completely self-contained, and will typically run of a battery source for many yearsbefore the batteries need to be changed or charged. Embedded Wi-Fi modules provide a simplemeans of wirelessly enabling any device which communicates via a serial port.

Picture of the internals of anADSL modem/router.A modern example of an embedded system.Labelled parts include a microprocessor , RAM , and flash memory
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2. Characteristics

2.1. User interface

Embedded systemtext user interface using MicroVGA

Embedded systems range from no user interface at alldedicated only to one tasktocomplex graphical user interfaces that resemble modern computer desktop operating systems.

Simple embedded devices usebuttons,LEDs,graphic or character LCDs (for example popular

HD44780 LCD)with a simplemenu system.

More sophisticated devices which use a graphical screen with touch sensing or screen-

edge buttons provide flexibility while minimizing space used: the meaning of the buttons canchange with the screen, and selection involves the natural behavior of pointing at what's desired.

Handheld systems often have a screen with a "joystick button" for a pointing device.

Some systems provide user interface remotely with the help of a serial connection. This

approach gives several advantages: extends the capabilities of embedded system, avoids the cost

of a display, simplifiesBSP,allows us to build rich user interface on the PC. A good example ofthis is the combination of anembedded web server running on an embedded device (such as an

IP camera) or a network routers. The user interface is displayed in a web browser on a PC

connected to the device, therefore needing no bespoke software to be installed.

2.2. Processors in embedded systems

Embedded processors can be broken into two broad categories. Ordinary microprocessorsuse separate integrated circuits for memory and peripherals. Microcontrollers have many more

peripherals on chip, reducing power consumption, size and cost. In contrast to the personalcomputer market, many different basic CPU architectures are used, since software is custom-

developed for an application and is not a commodity product installed by the end user. BothVon

Neumann as well as various degrees of Harvard architectures are used. RISC as well as non-

RISC processors are found. Word lengths vary from 4-bit to 64-bits and beyond, although the
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most typical remain 8/16-bit. Most architectures come in a large number of different variants and

shapes, many of which are also manufactured by several different companies.

Numerous microcontrollers have been developed for embedded systems use. General-purpose

microprocessors are also used in embedded systems, but generally require more support circuitry

than microcontrollers.

2.3 Peripherals

A close-up of the SMSC LAN91C110 (SMSC 91x) chip, an embeddedEthernet chip.

Embedded Systems talk with the outside world viaperipherals,such as:

Serial Communication Interfaces Synchronous Serial Communication Interface Universal Serial Bus (USB) Multi Media Cards

Networks Field buses Timers Discrete IO Analog to Digital/Digital to Analog Debugging

2.4. Tools

As with other software, embedded system designers use compilers, assemblers, anddebuggers to develop embedded system software. However, they may also use some more

specific tools:

In circuit debuggers or emulators (see next section). Utilities to add a checksum orCRC to a program, so the embedded system can check if

the program is valid.

For systems usingdigital signal processing,developers may use a math workbench suchas Scilab / Scicos, MATLAB / Simulink, EICASLAB, MathCad, Mathematica,or
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FlowStone DSP to simulate the mathematics. They might also use libraries for both the

host and target which eliminates developing DSP routines as done in DSPnano RTOS

andUnison Operating System.

A model based development tool likeVisSim lets you create and simulate graphical dataflow and UML State chart diagrams of components like digital filters, motor controllers,

communication protocol decoding and multi-rate tasks. Interrupt handlers can also becreated graphically. After simulation, you can automatically generate C-code to theVisSimRTOS which handles the main control task andpreemption of background tasks,

as well as automatic setup and programming of on-chip peripherals.

Custom compilers and linkers may be used to optimize specialized hardware. An embedded system may have its own special language or design tool, or add

enhancements to an existing language such asForth orBasic.

Another alternative is to add areal-time operating system orembedded operating system,which may have DSP capabilities likeDSPnano RTOS.

Modeling and code generatingtools often based onstate machines

Software tools can come from several sources:

Software companies that specialize in the embedded market Ported from theGNU software development tools Sometimes, development tools for a personal computer can be used if the embedded

processor is a close relative to a common PC processor

As the complexity of embedded systems grows, higher level tools and operating systems are

migrating into machinery where it makes sense. For example, cellphones,personal digital

assistants and other consumer computers often need significant software that is purchased orprovided by a person other than the manufacturer of the electronics. In these systems, an open

programming environment such asLinux,NetBSD,OSGi orEmbedded Java is required so thatthe third-party software provider can sell to a large market.

2.5 Debugging

Embedded debugging may be performed at different levels, depending on the facilities

available. From simplest to most sophisticate they can be roughly grouped into the followingareas:

Interactive resident debugging, using the simple shell provided by the embeddedoperating system (e.g. Forth and Basic)

External debugging using logging or serial port output to trace operation using either amonitor in flash or using a debug server like theRemedy Debugger which even works forheterogeneousmulticore systems.

An in-circuit debugger (ICD), a hardware device that connects to the microprocessor viaa JTAG or Nexus interface. This allows the operation of the microprocessor to be

controlled externally, but is typically restricted to specific debugging capabilities in theprocessor.
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An in-circuit emulator (ICE) replaces the microprocessor with a simulated equivalent,providing full control over all aspects of the microprocessor.

A completeemulatorprovides a simulation of all aspects of the hardware, allowing all ofit to be controlled and modified and allowing debugging on a normal PC. The downsides

are expense and slow operation, in some cases up to 100X slower than the final system.

For SoC designs, the typical approach is to verify and debug the design on an FPGAprototype board. Tools such as Certus are used to insert probes in the FPGA RTL thatmake signals available for observation. This is used to debug hardware, firmware and

software interactions across multiple FPGA with capabilities similar to a logic analyzer.

Unless restricted to external debugging, the programmer can typically load and run software

through the tools, view the code running in the processor, and start or stop its operation. The

view of the code may be asHLLsource-code,assembly code or mixture of both.

Because an embedded system is often composed of a wide variety of elements, the debugging

strategy may vary. For instance, debugging a software- (and microprocessor-) centric embedded

system is different from debugging an embedded system where most of the processing isperformed by peripherals (DSP, FPGA, and co-processor). An increasing number of embedded

systems today use more than one single processor core. A common problem with multi-coredevelopment is the proper synchronization of software execution. In such a case, the embedded

system design may wish to check the data traffic on the busses between the processor cores,

which requires very low-level debugging, at signal/bus level, with alogic analyzer,for instance.

2.6 Reliability

Embedded systems often reside in machines that are expected to run continuously for

years without errors, and in some cases recover by themselves if an error occurs. Therefore the

software is usually developed and tested more carefully than that for personal computers, andunreliable mechanical moving parts such as disk drives, switches or buttons are avoided.

Specific reliability issues may include:

The system cannot safely be shut down for repair, or it is too inaccessible to repair.Examples include space systems, undersea cables, navigational beacons, bore-hole

systems, and automobiles.

The system must be kept running for safety reasons. "Limp modes" are less tolerable.Often backups are selected by an operator. Examples include aircraft navigation, reactorcontrol systems, safety-critical chemical factory controls, train signals.

The system will lose large amounts of money when shut down: Telephone switches,factory controls, bridge and elevator controls, funds transfer and market making,automated sales and service.

A variety of techniques are used, sometimes in combination, to recover from errorsboth

software bugs such as memory leaks, and alsosoft errors in the hardware:
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watchdog timer that resets the computer unless the software periodically notifies thewatchdog

subsystems with redundant spares that can be switched over to software "limp modes" that provide partial function Designing with aTrusted Computing Base (TCB) architecture ensures a highly secure &

reliable system environment An Embedded Hypervisor is able to provide secure encapsulation for any subsystem

component, so that a compromised software component cannot interfere with other

subsystems, or privileged-level system software. This encapsulation keeps faults from

propagating from one subsystem to another, improving reliability. This may also allow asubsystem to be automatically shut down and restarted on fault detection.

Immunity Aware Programming
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3. Embedded Software Architectures

There are several different types of software architecture in common use.

3.1 Simple control loop

In this design, the software simply has a loop. The loop calls subroutines, each of which

manages a part of the hardware or software.

3.2Interrupt controlled systemSome embedded systems are predominantly interrupt controlled. This means that tasks

performed by the system are triggered by different kinds of events. An interrupt could begenerated for example by a timer in a predefined frequency, or by a serial port controller

receiving a byte.

These kinds of systems are used if event handlers need low latency and the event handlers are

short and simple.

Usually these kinds of systems run a simple task in a main loop also, but this task is not verysensitive to unexpected delays.

Sometimes the interrupt handler will add longer tasks to a queue structure. Later, after the

interrupt handler has finished, these tasks are executed by the main loop. This method brings thesystem close to a multitasking kernel with discrete processes.

Cooperative multitaskingAnonpreemptive multitasking system is very similar to the simple control loop scheme, except

that the loop is hidden in anAPI.The programmer defines a series of tasks, and each task gets itsown environment to run in. When a task is idle, it calls an idle routine, usually called pause,

wait, yield, nop

The advantages and disadvantages are to the control loop, except that adding new software is

easier, by simply writing a new task, or adding to the queue

Preemptive multitasking or multi-threadingIn this type of system, a low-level piece of code switches between tasks or threads based on a

timer (connected to an interrupt). This is the level at which the system is generally considered tohave an "operating system" kernel. Depending on how much functionality is required, it
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introduces more or less of the complexities of managing multiple tasks running conceptually in

parallel.

As any code can potentially damage the data of another task (except in larger systems using an

MMU) programs must be carefully designed and tested, and access to shared data must be

controlled by some synchronization strategy, such as message queues, semaphores or a non-blocking synchronization scheme.

Because of these complexities, it is common for organizations to use a real-time operatingsystem (RTOS), allowing the application programmers to concentrate on device functionality

rather than operating system services, at least for large systems; smaller systems often cannot

afford the overhead associated with a generic real time system, due to limitations regardingmemory size, performance, or battery life. The choice that an RTOS is required brings in its own

issues however as the selection must be done prior to starting to the application development

process. This timing forces developers to choose the embedded operating system for their device

based upon current requirements and so restricts future options to a large extent.[10]

The

restriction of future options becomes more of an issue as product life decreases. Additionally thelevel of complexity is continuously growing as devices are required to manage many variables

such as serial, USB, TCP/IP, Bluetooth, Wireless LAN, trunk radio, multiple channels, data andvoice, enhanced graphics, multiple states, multiple threads, numerous wait states and so on.

These trends are leading to the uptake of embedded middleware in addition to a real time

operating system.

Microkernels and exokernelsA microkernel is a logical step up from a real-time OS. The usual arrangement is that the

operating system kernel allocates memory and switches the CPU to different threads ofexecution. User mode processes implement major functions such as file systems, network

interfaces, etc.

In general, microkernels succeed when the task switching and intertask communication is fast,

and fail when they are slow.

Exokernels communicate efficiently by normal subroutine calls. The hardware and all the

software in the system are available to, and extensible by application programmers.

Monolithic kernelsIn this case, a relatively large kernel with sophisticated capabilities is adapted to suit anembedded environment. This gives programmers an environment similar to a desktop operating

system likeLinux orMicrosoft Windows,and is therefore very productive for development; on
http://en.wikipedia.org/wiki/Memory_management_unithttp://en.wikipedia.org/wiki/Message_queuehttp://en.wikipedia.org/wiki/Semaphore_%28programming%29http://en.wikipedia.org/wiki/Non-blocking_synchronizationhttp://en.wikipedia.org/wiki/Non-blocking_synchronizationhttp://en.wikipedia.org/wiki/Real-time_operating_systemhttp://en.wikipedia.org/wiki/Real-time_operating_systemhttp://c/Documents%20and%20Settings/PRINCE/My%20Documents/nakul/Embedded%20system%20-%20Wikipedia,%20the%20free%20encyclopedia.htm%23cite_note-11http://c/Documents%20and%20Settings/PRINCE/My%20Documents/nakul/Embedded%20system%20-%20Wikipedia,%20the%20free%20encyclopedia.htm%23cite_note-11http://c/Documents%20and%20Settings/PRINCE/My%20Documents/nakul/Embedded%20system%20-%20Wikipedia,%20the%20free%20encyclopedia.htm%23cite_note-11http://en.wikipedia.org/w/index.php?title=Embedded_middleware&action=edit&redlink=1http://en.wikipedia.org/wiki/Microkernelhttp://en.wikipedia.org/wiki/Exokernelhttp://en.wikipedia.org/wiki/Linuxhttp://en.wikipedia.org/wiki/Microsoft_Windowshttp://en.wikipedia.org/wiki/Microsoft_Windowshttp://en.wikipedia.org/wiki/Linuxhttp://en.wikipedia.org/wiki/Exokernelhttp://en.wikipedia.org/wiki/Microkernelhttp://en.wikipedia.org/w/index.php?title=Embedded_middleware&action=edit&redlink=1http://c/Documents%20and%20Settings/PRINCE/My%20Documents/nakul/Embedded%20system%20-%20Wikipedia,%20the%20free%20encyclopedia.htm%23cite_note-11http://en.wikipedia.org/wiki/Real-time_operating_systemhttp://en.wikipedia.org/wiki/Real-time_operating_systemhttp://en.wikipedia.org/wiki/Non-blocking_synchronizationhttp://en.wikipedia.org/wiki/Non-blocking_synchronizationhttp://en.wikipedia.org/wiki/Semaphore_%28programming%29http://en.wikipedia.org/wiki/Message_queuehttp://en.wikipedia.org/wiki/Memory_management_unit


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the downside, it requires considerably more hardware resources, is often more expensive, and

because of the complexity of these kernels can be less predictable and reliable.

Common examples of embedded monolithic kernels areEmbedded Linux andWindows CE.

Despite the increased cost in hardware, this type of embedded system is increasing in popularity,especially on the more powerful embedded devices such as Wireless Routers and GPS

Navigation Systems.Here are some of the reasons:

Ports to common embedded chip sets are available. They permit re-use of publicly available code for Device Drivers, Web Servers,

Firewalls,and other code.

Development systems can start out with broad feature-sets, and then the distribution canbe configured to exclude unneeded functionality, and save the expense of the memory

that it would consume.

Many engineers believe that running application code in user mode is more reliable,easier to debug and that therefore the development process is easier and the code moreportable.

Many embedded systems lack the tight real time requirements of a control system.Although a system such as Embedded Linux may be fast enough in order to respond to

many other applications.

Features requiring faster response than can be guaranteed can often be placed inhardware.

Exotic custom operating systemsA small fraction of embedded systems require safe, timely, reliable or efficient behavior

unobtainable with any of the above architectures. In this case an organization builds a system tosuit. In some cases, the system may be partitioned into a "mechanism controller" using specialtechniques, and a "display controller" with a conventional operating system. A communication

system passes data between the two.

Additional software componentsIn addition to the core operating system, many embedded systems have additional upper-layer

software components. These components consist of networking protocol stacks like CAN,TCP/IP, FTP, HTTP, and HTTPS, and also included storage capabilities like FAT and flash

memory management systems. If the embedded device has audio and video capabilities, then the

appropriate drivers and codec will be present in the system. In the case of the monolithic kernels,many of these software layers are included. In the RTOS category, the availability of theadditional software components depends upon the commercial offering.
http://en.wikipedia.org/wiki/Embedded_Linuxhttp://en.wikipedia.org/wiki/Windows_CEhttp://en.wikipedia.org/wiki/Router_%28computing%29http://en.wikipedia.org/wiki/Automotive_navigation_systemhttp://en.wikipedia.org/wiki/Automotive_navigation_systemhttp://en.wikipedia.org/wiki/Device_driverhttp://en.wikipedia.org/wiki/Web_servershttp://en.wikipedia.org/wiki/Firewall_%28networking%29http://en.wikipedia.org/wiki/Programmable_logic_devicehttp://en.wikipedia.org/wiki/Controller%E2%80%93area_networkhttp://en.wikipedia.org/wiki/TCP/IPhttp://en.wikipedia.org/wiki/FTPhttp://en.wikipedia.org/wiki/HTTPhttp://en.wikipedia.org/wiki/HTTPShttp://en.wikipedia.org/wiki/File_Allocation_Tablehttp://en.wikipedia.org/wiki/File_Allocation_Tablehttp://en.wikipedia.org/wiki/HTTPShttp://en.wikipedia.org/wiki/HTTPhttp://en.wikipedia.org/wiki/FTPhttp://en.wikipedia.org/wiki/TCP/IPhttp://en.wikipedia.org/wiki/Controller%E2%80%93area_networkhttp://en.wikipedia.org/wiki/Programmable_logic_devicehttp://en.wikipedia.org/wiki/Firewall_%28networking%29http://en.wikipedia.org/wiki/Web_servershttp://en.wikipedia.org/wiki/Device_driverhttp://en.wikipedia.org/wiki/Automotive_navigation_systemhttp://en.wikipedia.org/wiki/Automotive_navigation_systemhttp://en.wikipedia.org/wiki/Router_%28computing%29http://en.wikipedia.org/wiki/Windows_CEhttp://en.wikipedia.org/wiki/Embedded_Linux


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Embedded Systems

By Nakul

Structure of the seminar

Introduction

Characteristics

Embedded systems for meters


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What is an Embedded System ?

An embedded system is a special-

purpose computer system designed

to perform a dedicated function

Characteristics of Embedded Systems

1. Interface

2. Tools

3. Reliability

4. Volume


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1. Interface

Interface

No UserInterface

Full UserInterface

Performing user-defined

Dedicated to oneTask

2. Tools

Embedded system designers usecompilers, assemblers, and debuggers

Utilities to add a checksum or CRC to aprogram

Emulator replaces the microprocessorwith a simulated equivalent


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3. Reliability issues

System cannot be shut down for repair

Solutions involve subsystems withspares

system must be kept running for safetyand monetary reasons

4. Volume

Volume

High Volume Low Volume

Minimizing cost is

usually the primary

design consideration

Used when cost is not amajor factor

Performance and reliabilityconstraints


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Limitations of the meter

Mechanical device

Prone to wear,shock

Maintains no record of time

Only Counts the number of rotations ofthe wheel

Real power limitation

Ideally current and voltage are in phase

Every volt-ampere delivered becomes awatt of power used

Induction motors and lamp ballastscause current to flow out of phase

Fewer actual watts are used thandelivered


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Design Fundamentals

1. Means of taking samples

2. Display

3. Communication subsystem

4. Non-volatile memory

5. Power supply

6. Stored program micro-controller

Choosing a micro-controller

Feature set

Code spaceData Space

Data converter

Real-time clock


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Conclusion

A quiet revolution is in progress in theutility industry.

Static metering devices, have been inuse for the better part of a century

Gradually being replaced with multi-rate, multifunction meters

Capable of more accurately accountingfor utility usage.