EMBEDDED SYSTEMS

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basics of embedded systems

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EMBEDDED SYSTEMS: 

BY R.MUGESH K.SATHISH KUMAR EMBEDDED SYSTEMS

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INTRODUCTION: An embedded system is a computer system designed for specific control functions within a larger system, often with real-time computing constraints . The embedded system is a combination of hardware and software to perform a particular task. It is a general-purpose computer, such as a personal computer (PC), is designed to be flexible and to meet a wide range of end-user needs . Embedded systems contain processing cores that are typically either microcontrollers or digital signal processors (DSP ). Embedded systems control many devices in common use today . Physically, embedded systems range from portable devices such as digital watches and MP3 players, to large stationary installations like traffic lights, factory controllers, or the systems controlling nuclear power plants.

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HISTORY: One of the first recognizably modern embedded systems was the Apollo Guidance Computer, developed by Charles Stark Draper at the MIT Instrumentation Laboratory . The first microprocessor for example, the Intel 4004, was designed for calculators and other small systems but still required many external memory and support chips . In 1978 National Engineering Manufacturers Association released a "standard" for programmable microcontrollers, including almost any computer-based controllers, such as single board computers, numerical, and event-based controllers . As the cost of microprocessors and microcontrollers fell it became feasible to replace expensive knob-based analog components such as potentiometers and variable capacitors with up/down buttons or knobs read out by a microprocessor. The integration of microcontrollers has further increased the applications for which embedded systems are used into areas where traditionally a computer would not have been considered.

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FEATURES: Small size & less weight. More efficency . Embedded systems are programmed to perform specific task only. Embedded systems are playing important roles in our lives every day. ADVANTAGES: High reliable . Can be interface as user convenient. Embedded systems are constrained for power consumption since many embedded systems work on a battery at low power.

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CHARACTERISTCS: Embedded systems are designed to do some specific task, rather than be a general-purpose computer for multiple tasks. Some also have real-time performance constraints that must be met, for reasons such as safety and usability; others may have low or no performance requirements, allowing the system hardware to be simplified to reduce costs. Embedded systems are not always standalone devices. Many embedded systems consist of small, computerized parts within a larger device that serves a more general purpose. For example, the Gibson Robot Guitar features an embedded system for tuning the strings, but the overall purpose of the Robot Guitar is, of course, to play music . The program instructions written for embedded systems are referred to as firmware , and are stored in read-only memory or Flash memory chips. They run with limited computer hardware resources: little memory, small or non-existent keyboard or screen.

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User interface: Simple embedded devices use buttons, LEDs, graphic or character LCDs (for example popular HD44780 LCD) with a simple menu system . 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 (e.g. RS-232, USB, I²C, etc.) or network (e.g. Ethernet) connection.

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PROCESSORS: Secondly, Embedded processors can be broken into two broad categories: ordinary microprocessors (μP) and microcontrollers (μC), which have many more peripherals on chip, reducing cost and size. Contrasting to the personal computer and server markets, a fairly large number of basic CPU architectures are used; there are Von Neumann as well as various degrees of Harvard architectures , RISC as well as non-RISC and VLIW; word lengths vary from 4-bit to 64-bits and beyond (mainly in DSP processors) although the most typical remain 8/16-bit.

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Ready made computer boards: In certain applications, where small size or power efficiency are not primary concerns, the components used may be compatible with those used in general purpose x86 personal computers. Boards such as the VIA EPIA range help to bridge the gap by being PC-compatible but highly integrated, physically smaller or have other attributes making them attractive to embedded engineers . Systems built in this way are still regarded as embedded since they are integrated into larger devices and full fill a single role. Examples of devices that may adopt this approach are ATMs and arcade machines, which contain code specific to the application . When a System-on-a-chip processor is involved, there may be little benefit to having a standardized bus connecting discrete components, and the environment for both hardware and software tools may be very different.

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ASIC and FPGA solutions A common array of n configuration for very-high-volume embedded systems is the system on a chip (SoC) which contains a complete system consisting of multiple processors, multipliers, caches and interfaces on a single chip. SoCs can be implemented as an application-specific integrated circuit (ASIC) or using a field-programmable gate array (FPGA ).

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Peripherals: Serial Communication Interfaces (SCI): RS-232 , RS-422 , RS-485 etc. Synchronous Serial Communication Interface: I2C , SPI , SSC and ESSI (Enhanced Synchronous Serial Interface) Universal Serial Bus (USB) Multi Media Cards (SD Cards, Compact Flash etc.) Networks: Ethernet , Lon Works , etc. Fieldbuses : CAN-Bus , LIN-Bus , PROFIBUS , etc. Timers: PLL (s), Capture/Compare and Time Processing Units Discrete IO: General Purpose Input/output (GPIO) Analog to Digital/Digital to Analog ( ADC / DAC ) Debugging: JTAG , ISP , ICSP , BDM Port, BITP, and DP9 ports.

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Debugging: Embedded debugging may be performed at different levels, depending on the facilities available. From simplest to most sophisticated they can be roughly grouped into the following areas: Interactive resident debugging, using the simple shell provided by the embedded operating system (e.g. Forth and Basic) External debugging using logging or serial port output to trace operation using either a monitor in flash or using a debug server like theRemedy Debugger which even works for heterogeneous multicore systems. An in-circuit debugger (ICD), a hardware device that connects to the microprocessor via a JTAG or Nexus interface. This allows the operation of the microprocessor to be controlled externally, but is typically restricted to specific debugging capabilities in the processor. An in-circuit emulator (ICE) replaces the microprocessor with a simulated equivalent, providing full control over all aspects of the microprocessor. A complete emulator provides a simulation of all aspects of the hardware, allowing all of it to be controlled and modified, and allowing debugging on a normal PC.

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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, and unreliable 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, reactor control 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.

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High vs low volume: For high volume systems such as portable music players or mobile phones, minimizing cost is usually the primary design consideration. Engineers typically select hardware that is just “good enough” to implement the necessary functions. For low-volume or prototype embedded systems, general purpose computers may be adapted by limiting the programs or by replacing the operating system with a real-time operating system.

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CONCLUSION: Embedded systems are designed to do some specific task, rather than be a general-purpose computer for multiple tasks. Some also have real-time performance constraints that must be met, for reasons such as safety and usability; others may have low or no performance requirements, allowing the system hardware to be simplified to reduce costs . Embedded systems are not always standalone devices.