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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.