An embedded system is defined as a device consisting of a processor, memory, and input/output units and having a specific function within a larger system.
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Embedded systems have applications in the consumer, home entertainment, industrial, medical, automotive, commercial, telecommunication, military, and aerospace verticals.
This article covers the meaning, components, and applications of embedded systems.
An embedded system consists of a processor, memory, and input/output units and has a specific function within a larger system. Embedded systems have applications in the consumer, home entertainment, industrial, medical, automotive, commercial, telecommunication, military, and aerospace verticals.
Embedded systems are also called embedded computers. Generally speaking, they are small in form factor and drive specific computing tasks. While they are usually part of larger systems (thus the moniker &#;embedded&#;), they can serve as standalone devices too. Embedded systems are useful in applications with size, power, cost, or weight constraints.
How do embedded systems work?
Embedded systems are computers. Therefore, like most other computers, they contain a combination of hardware and software such as microprocessors, microcontrollers, volatile and non-volatile memory, graphics processing units (GPUs), input/output communication interfaces and ports, power supplies, and system and application code. However, embedded systems have four main factors that differentiate them from a typical workstation or server: purpose, design, cost, and human involvement.
Like any other computer, embedded systems leverage printed circuit boards (PCBs) programmed with software that guides the hardware on operation and data management using memory and input/output communication interfaces. The result is the terminal production of output that is of value to the end user. As such, at a fundamental level, embedded systems are not too different from workstations and servers.
Types of embedded systems
When considering performance and functional requirements, embedded systems are categorized into real-time embedded systems, standalone embedded systems, networked embedded systems, and mobile embedded systems.
prioritize prompt output generation and can be classified as soft real-time (lenient deadlines) or hard real-time (strict deadlines).
can function independently without a host computer.
rely on network connections and communication for output generation.
refer to small, portable devices such as smartphones and laptops.
Finally, when classified based on microcontroller performance, embedded systems are divided into small-scale, medium-scale, and sophisticated categories, depending on the bit size of the microcontroller.
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The components of embedded systems consist of hardware and software elements that work together to enable the desired functionality of the system.
Hardware components of embedded systems
The hardware components of embedded systems encompass various physical elements that comprise the system infrastructure. These include power supply, microcontrollers and microprocessors, memory, timers and counters, communication interfaces, input/output, and electrical circuits, all of which work together to enable the desired functionality of the embedded system.
The power supply component is an electrical unit responsible for powering up the electrical load of the embedded system. While a 5V power supply is generally required, the range can go from 1.8V to 3.3V, depending on the application.
To ensure seamless system operations, a smooth and efficient power supply is a must. The power supply unit can either be live (such as from a wall adapter) or battery-powered. Some embedded systems use an independent power supply, while others leverage the same source as the larger technology being powered.
Embedded systems come in two key variants: microcontroller-powered and microprocessor-powered. A form of integrated circuits, these components give the system its computing power. In simple terms, the microcontroller or microprocessor serves as the brain of the embedded system and drives its performance.
Processors range from 8-bit to 16-bit to 32-bit, with the main difference in processing speed and throughput. For instance, a 32-bit processor has a higher processing speed since it can manipulate 32 bits at once, while a 16-bit processor has a comparatively lower processing speed as it manipulates only 16 bits at a time. So why don&#;t all embedded systems come fitted with 32-bit processors? It&#;s simple. Not all applications require high processing speed and associated higher costs!
The memory component is essential for storing critical data in embedded systems. This component is generally integrated into the microprocessor or microcontroller. The two types of memory are RAM (random access memory) and ROM (read-only memory).
RAM is also known as the &#;data memory&#; and is volatile, which means that it stores information only temporarily and is wiped clean when the power supply is turned off. On the other hand, ROM is also known as the &#;code memory&#; and is responsible for storing the program code. It is non-volatile, storing system information even when the power supply is turned off.
Timers are used in applications requiring the creation of a delay before the execution of a specific function by the embedded system. On the other hand, counters are used in applications where the number of times a specific event takes place needs to be tracked. Up counters count upward from the starting value to 0xFF, while down counters count downward to 0x00. Counters are integrated into the system using register-type circuits.
Input components allow other components within the larger interconnected infrastructure to interact with the embedded system. For instance, a sensor helps provide inputs for the system to process. Once processing is complete (for instance, counting), the results are communicated to the required destination via the output component.
Communication interfaces enable embedded systems to establish communications with each other and other components within the larger system. Different interfaces include USB, I2C, UART, RS-485, and SPI. For simple applications, communication ports within the microcontroller are utilized, and ports can be externally installed in case of advanced applications.
Depending on the application, embedded systems can contain customized electrical circuits. Some of the basic components used in electrical circuits of embedded systems are:
The PCB is a crucial component within the electrical circuit of embedded systems. It is a mechanical circuit board that uses conductive copper traces to link other components electronically. Electronic circuits made using a PCB are more cost-effective and operationally efficient than wire wrap or point-to-point configurations.
The resistor is an electrical component primarily responsible for producing resistance in the current flow. It reduces current flow in a calculated manner to adjust signal levels. Motor controls and power distribution systems use high-power resistors to dissipate more heat.
The resistor&#;s electrical function depends on its resistance; the greater the resistance, the more resistance is created in the current flow. Resistors are subdivided into fixed and variable, with fixed resistors changing their resistance with temperature and variable resistors leveraged as sensing devices for light, humidity, heat, and force.
A capacitor is an electrical circuit component with two terminals. It is mainly used for energy storage and release as the circuit requires. While capacitors come in various forms, most feature two electrical conductors separated using a dielectric material. Capacitors are used for various applications, including smoothing, bypassing, and filtering electrical signals.
A diode allows the current to flow in only a single direction. This component is generally made of semiconductor materials such as silicon or germanium. It is useful for applications such as switches, signal mixers, logic gates, voltage regulators, limiters, clippers, gain control circuits, and clampers.
In the electrical circuit, transistors are responsible for switching and amplification. They come in two main types: metal-oxide-semiconductor field-effect transistor (MOSFET), which is a voltage-controlled component with terminals such as source, gate, and drain; and bipolar junction transistor, which is a current-controlled component with terminals such as base, emitter, and collector.
Transistors are used in various applications such as computers, aircraft, pacemakers, stoves, and motor control. This component works on a simple principle: the small current at one terminal produces a large current in the other terminals for amplification.
The integrated circuit combines numerous electrical components within one chip. It helps users by providing a ready-made chip that can be directly incorporated into the embedded system without capacitors and resistors having to be added separately. Integrated chips can function as oscillators, microprocessors, amplifiers, memory units, timers, and more.
LEDs are widely used in electrical circuits to indicate whether the circuit functions correctly. LEDs allow users to identify the state of current within the circuit.
Finally, the inductor is an electrical component for energy storage in an electric field and within the presence of an electrical current. An inductor takes the form of an insulated wire encircling a coil. It blocks alternating current while allowing direct current to flow. Inductors used for this function are known as &#;chokes.&#;
Software components of embedded systems
Unlike computer software, which can be installed on different devices to achieve the same goal, embedded system software is specifically written for a particular type of device, and its goals are much narrower in scope. The software components of embedded systems are:
A text editor is the first software component needed for building an embedded system. This editor is used to write source code in C and C++ programming languages and save it as a text file.
This component&#;s core function is the development of an executable program. Once the code is prepared in the text editor, the machine must understand it. This is achieved with the compiler&#;s help, translating the written code into low-level machine language. Examples of low-level languages include machine code, assembly language, and object code.
The assembler is for instances where assembly language is the programming language used to build the application. The assembly language program is translated into HEX code for further processing. Once the code is written, the programmer is used to write the program on the chip.
This is slightly different than the process followed in a compiler. In the compiler, written code is directly converted into machine language. On the other hand, the assembler first converts source code to object code, after which the object code is converted into machine language.
This component makes the embedded system behave like a real, live system while operating in a simulation environment. Simply put, it simulates software performance and helps ensure that the performance of the written code is ideal. The emulator is used to gain an idea of the way the code will operate in real time.
Software code is generally written in small-sized pieces and modules. The link editor, also known as a &#;linker,&#; is the component used to take one or more object files and integrate them to develop a single executable code.
Finally, the debugger is a software component used for debugging and testing. It is responsible for scanning the code, removing bugs and other errors, and highlighting the specific instances where they occurred. The debugger helps programmers address errors swiftly.
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Embedded systems are crucial in several technologies, including the internet of things (IoT) and machine-to-machine (M2M) devices. Almost every smart device today uses this versatile technology in some capacity or the other.
A few real-world applications of embedded systems are:
Embedded Systems Applications
1. GPS
The global positioning system (GPS) uses satellites and receivers to synchronize location, velocity, and time data to provide a navigation system the world can use. GPS systems are commonly used in vehicles and mobile devices. All &#;receivers&#; (devices that receive GPS data) are integrated with embedded systems to enable the use of the global positioning system.
2. Medical devices
Cutting-edge medical devices with embedded systems are used for patients requiring constant monitoring. For instance, embedded sensors gather health data such as readings from implants, pulse rate, and heart rate. This data is then transmitted to a private cloud, where it can be reviewed automatically by an alert system or manually by a medical professional.
3. Automotive
Embedded systems in automotive applications enhance overall safety and user experience. Key examples of embedded systems in action are adaptive speed control, pedestrian recognition, car breakdown warning, merging assistance, airbag deployment, anti-lock braking system, and in-vehicle entertainment equipment.
4. Automated fare collection
Automated fare collection solutions enable public transportation passengers to pay their fares through automated machines or even online without interacting with another human being. The automatic transit fare collection ecosystem consists of ticketing machines, magnetic stripe cards and smart cards for regular travelers, ticket and card checking machines, and automatic gate machines. All these components include embedded systems to enable them to communicate with each other and thus keep the mechanism operational.
5. Fitness trackers
Fitness trackers have become increasingly popular wearable devices that monitor health metrics and track activities such as running, walking, and sleeping. These devices leverage embedded systems for data collection such as heart rate, body temperature, and steps walked. This data is transmitted to servers via a wide area network (WAN) such as LTE or GPRS.
6. Home entertainment
Entertainment systems such as televisions are a mainstay in homes worldwide. Embedded systems are key in reading inputs from connectors, such as the antenna, DisplayPort, HDMI, and Ethernet. Besides this, remote controls transmit infrared signals for reading by televisions. Smart televisions even include an operating system that supports internet and streaming applications. Embedded systems play an important role in these functions and are gaining more ground as new ways to make home entertainment even smarter are discovered.
7. Automated teller machines
Automated teller machines (ATMs) are large computerized electronic devices used globally in the banking sector. During a transaction, an ATM communicates with its host bank computer over a network connection. The bank computer verifies the data entered during the transaction and stores processed information. At the same time, the ATM uses embedded systems to process user inputs from the field and display the transaction data from the bank computer.
8. Manufacturing
Factories today use robots in several processes that require high-precision tasks, operating in dangerous work conditions, or both. Typical automated jobs require robots to be fitted with sensors, actuators, and software that allow them to &#;perceive&#; the environment and derive the required output efficiently and safely. Robots are equipped with embedded systems that link them to various subsystems to achieve this goal.
Plant automation robots would have to rely on external computing and control systems without these embedded systems. This can lead to increased safety risks due to delays in human response or connection failure. Therefore, as Industry 4.0 becomes an all-pervasive reality, plant automation systems are increasingly being integrated with embedded systems equipped with artificial intelligence and machine learning to make equipment safer, more efficient, and smarter.
For instance, these systems allow machines to automatically identify and remove defects from production before the human eye can see them. Factory robots with embedded systems have many applications, including assembly and quality assurance.
9. Electric vehicle charging stations
Electric vehicle charging stations supply electric power to recharge the batteries of connected electric vehicles. Embedded systems are used in charging stations to provide computing power for graphics displays, automatically highlight technical issues, and alert technicians about upcoming maintenance requirements, among other functions.
10. Self-service kiosks
Finally, we have interactive self-service kiosks that offer users information and services in environments where a human employee&#;s presence is unfeasible. Think of a ticketing kiosk catering to moviegoers for a 2 a.m. screening at a mostly empty theater. Self-service kiosks come in various forms, from snack vending machines to refueling stations with self-checkout equipment. These kiosks can be found at airports, retail stores, hospitals, government buildings, and many other locations. Embedded systems provide the computing power required for these kiosks to offer customers an interactive experience.
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Takeaway
Embedded systems are small computers integrated into various larger systems and execute specific tasks such as graphics and data processing. They are widely used in the modern world and significantly impact how we entertain ourselves, commute, run commercial operations, and carry out various other day-to-day activities.
Everything from elevators and point-of-sale machines to printers and routers to vehicles and EV charging stations contains embedded devices. Simply put, they are found everywhere in today&#;s world. They may be small in size but are swift in processing speed, purpose-built, and hardy. They drive the high-quality performance of applications in real-time. Embedded systems are also becoming increasingly powerful and sophisticated, thus enhancing their applicability in edge computing, IoT, graphics rendering, and other functions.
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MORE ON GENERAL TECH
An embedded system on a plug-in card with processor, memory, power supply, and external interfaces
An embedded system is a specialized computer system&#;a combination of a computer processor, computer memory, and input/output peripheral devices&#;that has a dedicated function within a larger mechanical or electronic system.[1][2] It is embedded as part of a complete device often including electrical or electronic hardware and mechanical parts. Because an embedded system typically controls physical operations of the machine that it is embedded within, it often has real-time computing constraints. Embedded systems control many devices in common use.[3] In , it was estimated that ninety-eight percent of all microprocessors manufactured were used in embedded systems.[4][needs update]
Modern embedded systems are often based on microcontrollers (i.e. microprocessors with integrated memory and peripheral interfaces), but ordinary microprocessors (using external chips for memory and peripheral interface circuits) are also common, especially in more complex systems. In either case, the processor(s) used may be types ranging from general purpose to those specialized in a certain class of computations, or even custom designed for the application at hand. A common standard class of dedicated processors is the digital signal processor (DSP).
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 its reliability and performance. Some embedded systems are mass-produced, benefiting from economies of scale.
Embedded systems range in size from portable personal devices such as digital watches and MP3 players to bigger machines like home appliances, industrial assembly lines, robots, transport vehicles, traffic light controllers, and medical imaging systems. Often they constitute subsystems of other machines like avionics in aircraft and astrionics in spacecraft. Large installations like factories, pipelines, and electrical grids rely on multiple embedded systems networked together. Generalized through software customization, embedded systems such as programmable logic controllers frequently comprise their functional units.
Embedded systems range from those low in complexity, with a single microcontroller chip, to very high with multiple units, peripherals and networks, which may reside in equipment racks or across large geographical areas connected via long-distance communications lines.
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The origins of the microprocessor and the microcontroller can be traced back to the MOS integrated circuit, which is an integrated circuit chip fabricated from MOSFETs (metal&#;oxide&#;semiconductor field-effect transistors) and was developed in the early s. By , MOS chips had reached higher transistor density and lower manufacturing costs than bipolar chips. MOS chips further increased in complexity at a rate predicted by Moore's law, leading to large-scale integration (LSI) with hundreds of transistors on a single MOS chip by the late s. The application of MOS LSI chips to computing was the basis for the first microprocessors, as engineers began recognizing that a complete computer processor system could be contained on several MOS LSI chips.[5]
The first multi-chip microprocessors, the Four-Phase Systems AL1 in and the Garrett AiResearch MP944 in , were developed with multiple MOS LSI chips. The first single-chip microprocessor was the Intel , released in . It was developed by Federico Faggin, using his silicon-gate MOS technology, along with Intel engineers Marcian Hoff and Stan Mazor, and Busicom engineer Masatoshi Shima.[6]
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One of the first recognizably modern embedded systems was the Apollo Guidance Computer,[citation needed] developed ca. by Charles Stark Draper at the MIT Instrumentation Laboratory. At the project's inception, the Apollo guidance computer was considered the riskiest item in the Apollo project as it employed the then newly developed monolithic integrated circuits to reduce the computer's size and weight.
An early mass-produced embedded system was the Autonetics D-17 guidance computer for the Minuteman missile, released in . When the Minuteman II went into production in , the D-17 was replaced with a new computer that represented the first high-volume use of integrated circuits.
Since these early applications in the s, embedded systems have come down in price and there has been a dramatic rise in processing power and functionality. An early microprocessor, the Intel (released in ), was designed for calculators and other small systems but still required external memory and support chips. By the early s, memory, input and output system components had been integrated into the same chip as the processor forming a microcontroller. Microcontrollers find applications where a general-purpose computer would be too costly. As the cost of microprocessors and microcontrollers fell, the prevalence of embedded systems increased.
A comparatively low-cost microcontroller may be programmed to fulfill the same role as a large number of separate components. With microcontrollers, it became feasible to replace, even in consumer products, expensive knob-based analog components such as potentiometers and variable capacitors with up/down buttons or knobs read out by a microprocessor. Although in this context an embedded system is usually more complex than a traditional solution, most of the complexity is contained within the microcontroller itself. Very few additional components may be needed and most of the design effort is in the software. Software prototype and test can be quicker compared with the design and construction of a new circuit not using an embedded processor.
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Embedded Computer Sub-Assembly for Accupoll Electronic Voting Machine[
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Embedded systems are commonly found in consumer, industrial, automotive, home appliances, medical, telecommunication, commercial, aerospace and military applications.
Telecommunications systems employ numerous embedded systems from switches for the network to cell phones at the end user. Computer networking uses dedicated routers and network bridges to route data.
Consumer electronics include MP3 players, television sets, mobile phones, video game consoles, digital cameras, GPS receivers, and printers. Household appliances, such as microwave ovens, washing machines and dishwashers, include embedded systems to provide flexibility, efficiency and features. Advanced heating, ventilation, and air conditioning (HVAC) systems use networked thermostats to more accurately and efficiently control temperature that can change by time of day and season. Home automation uses wired- and wireless-networking that can be used 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. Spacecraft rely on astrionics systems for trajectory correction. Various electric motors &#; brushless DC motors, induction motors and DC motors &#; use electronic motor controllers. Automobiles, electric vehicles, and hybrid vehicles increasingly use embedded systems to maximize efficiency and reduce pollution. Other automotive safety systems using embedded systems include anti-lock braking system (ABS), electronic stability control (ESC/ESP), traction control (TCS) and automatic four-wheel drive.
Medical equipment uses embedded systems for monitoring, and various medical imaging (positron emission tomography (PET), single-photon emission computed tomography (SPECT), computed tomography (CT), and magnetic resonance imaging (MRI) for non-invasive internal inspections. Embedded systems within medical equipment are often powered by industrial computers.[8]
Embedded systems are used for safety-critical systems in aerospace and defense industries. Unless connected to wired or wireless networks via on-chip 3G cellular or other methods for IoT monitoring and control purposes, these systems can be isolated from hacking and thus be more secure.[citation needed] For fire safety, the systems can be designed to have a greater ability to handle higher temperatures 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.
Miniature wireless devices called motes are networked wireless sensors. Wireless sensor networking makes use of miniaturization made possible by advanced integrated circuit (IC) design to couple full wireless subsystems to sophisticated sensors, enabling people and companies to measure a myriad of things in the physical world and act on this information through monitoring and control systems. These motes are completely self-contained and will typically run off a battery source for years before the batteries need to be changed or charged.
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Embedded systems are designed to perform a specific task, in contrast with general-purpose computers designed for multiple tasks. Some 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 are a small part 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 to play music.[9] Similarly, an embedded system in an automobile provides a specific function as a subsystem of the car itself.
e-con Systems eSOM270 & eSOM300 Computer on ModulesThe 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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Embedded systems range from no user interface at all, in systems dedicated to one task, to complex graphical user interfaces that resemble modern computer desktop operating systems. Simple embedded devices use buttons, light-emitting diodes (LED), graphic or character liquid-crystal displays (LCD) with a simple menu system. More sophisticated devices that use a graphical screen with touch sensing or screen-edge soft keys provide flexibility while minimizing space used: the meaning of the buttons can change with the screen, and selection involves the natural behavior of pointing at what is desired.
Some systems provide user interface remotely with the help of a serial (e.g. RS-232) or network (e.g. Ethernet) connection. This approach extends the capabilities of the embedded system, avoids the cost of a display, simplifies the board support package (BSP) and allows designers to build a rich user interface on the PC. A good example of this is the combination of an embedded HTTP server running on an embedded device (such as an IP camera or a network router). The user interface is displayed in a web browser on a PC connected to the device.
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Examples of properties of typical embedded computers when compared with general-purpose counterparts, are low power consumption, small size, rugged operating ranges, and low per-unit cost. This comes at the expense of limited processing resources.
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.
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PC/104 and PC/104+ are examples of standards for ready-made computer boards intended for small, low-volume embedded and ruggedized systems. These are mostly x86-based and often physically small compared to a standard PC, although still quite large compared to most simple (8/16-bit) embedded systems. They may use DOS, FreeBSD, Linux, NetBSD, OpenHarmony or an embedded real-time operating system (RTOS) such as MicroC/OS-II, QNX or VxWorks.
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. The advantage of this approach is that low-cost commodity components may be used along with the same software development tools used for general software development. Systems built in this way are still regarded as embedded since they are integrated into larger devices and fulfill a single role. Examples of devices that may adopt this approach are automated teller machines (ATM) and arcade machines, which contain code specific to the application.
However, most ready-made embedded systems boards are not PC-centered and do not use the ISA or PCI busses. 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.
One common design style uses a small system module, perhaps the size of a business card, holding high density BGA chips such as an ARM-based system-on-a-chip processor and peripherals, external flash memory for storage, and DRAM for runtime memory. The module vendor will usually provide boot software and make sure there is a selection of operating systems, usually including Linux and some real-time choices. These modules can be manufactured in high volume, by organizations familiar with their specialized testing issues, and combined with much lower volume custom mainboards with application-specific external peripherals. Prominent examples of this approach include Arduino and Raspberry Pi.
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A system on a chip (SoC) contains a complete system - consisting of multiple processors, multipliers, caches, even different types of memory and commonly various peripherals like interfaces for wired or wireless communication on a single chip. Often graphics processing units (GPU) and DSPs are included such chips. SoCs can be implemented as an application-specific integrated circuit (ASIC) or using a field-programmable gate array (FPGA) which typically can be reconfigured.
ASIC implementations are common for very-high-volume embedded systems like mobile phones and smartphones. ASIC or FPGA implementations may be used for not-so-high-volume embedded systems with special needs in kind of signal processing performance, interfaces and reliability, like in avionics.
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A close-up of the SMSC LAN91C110 (SMSC 91x) chip, an embedded Ethernet chipEmbedded systems talk with the outside world via peripherals, such as:
As with other software, embedded system designers use compilers, assemblers, and debuggers to develop embedded system software. However, they may also use more specific tools:
Software tools can come from several sources:
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 or provided by a person other than the manufacturer of the electronics. In these systems, an open programming environment such as Linux, NetBSD, FreeBSD, OSGi or Embedded Java is required so that the third-party software provider can sell to a large market.
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Embedded debugging may be performed at different levels, depending on the facilities available. Considerations include: does it slow down the main application, how close is the debugged system or application to the actual system or application, how expressive are the triggers that can be set for debugging (e.g., inspecting the memory when a particular program counter value is reached), and what can be inspected in the debugging process (such as, only memory, or memory and registers, etc.).
From simplest to most sophisticated debugging techniques and systems are roughly grouped into the following areas:
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This allows the operation of the microprocessor to be controlled externally, but is typically restricted to specific debugging capabilities in the processor.[
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are used to insert probes in the FPGA implementation that make signals available for observation. This is used to debug hardware, firmware and software interactions across multiple FPGAs in an implementation 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 as high-level programming language, assembly code or mixture of both.
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Real-time operating systems often support tracing of operating system events. A graphical view is presented by a host PC tool, based on a recording of the system behavior. The trace recording can be performed in software, by the RTOS, or by special tracing hardware. RTOS tracing allows developers to understand timing and performance issues of the software system and gives a good understanding of the high-level system behaviors. Trace recording in embedded systems can be achieved using hardware or software solutions. Software-based trace recording does not require specialized debugging hardware and can be used to record traces in deployed devices, but it can have an impact on CPU and RAM usage.[13] One example of a software-based tracing method used in RTOS environments is the use of empty macros which are invoked by the operating system at strategic places in the code, and can be implemented to serve as hooks.
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Embedded systems often reside in machines that are expected to run continuously for years without error, 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:
A variety of techniques are used, sometimes in combination, to recover from errors&#;both software bugs such as memory leaks, and also soft errors in the hardware:
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For high-volume systems such as 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 an RTOS.
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In National Electrical Manufacturers Association released ICS 3-, a standard for programmable microcontrollers,[18] including almost any computer-based controllers, such as single-board computers, numerical, and event-based controllers.
There are several different types of software architecture in common use.
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In this design, the software simply has a loop which monitors the input devices. The loop calls subroutines, each of which manages a part of the hardware or software. Hence it is called a simple control loop or programmed input-output.
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Some embedded systems are predominantly controlled by interrupts. This means that tasks performed by the system are triggered by different kinds of events; an interrupt could be generated, for example, by a timer at a predefined interval, or by a serial port controller receiving data.
This architecture is used if event handlers need low latency, and the event handlers are short and simple. These systems run a simple task in a main loop also, but this task is not very sensitive 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 the system close to a multitasking kernel with discrete processes.
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Cooperative multitasking is very similar to the simple control loop scheme, except that the loop is hidden in an API.[3][1] The programmer defines a series of tasks, and each task gets its own environment to run in. When a task is idle, it calls an idle routine which passes control to another task.
The advantages and disadvantages are similar to that of the control loop, except that adding new software is easier, by simply writing a new task, or adding to the queue.
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In this type of system, a low-level piece of code switches between tasks or threads based on a timer invoking an interrupt. This is the level at which the system is generally considered to have an operating system kernel. Depending on how much functionality is required, it 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 systems using a memory management unit) 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 an off-the-shelf RTOS, allowing the application programmers to concentrate on device functionality rather than operating system services. The choice to include an RTOS brings in its own issues, however, as the selection must be made prior to starting the application development process. This timing forces developers to choose the embedded operating system for their device based on current requirements and so restricts future options to a large extent.[19]
The level of complexity in embedded systems is continuously growing as devices are required to manage peripherals and tasks such as serial, USB, TCP/IP, Bluetooth, Wireless LAN, trunk radio, multiple channels, data and voice, 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 an RTOS.
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A microkernel allocates memory and switches the CPU to different threads of execution. User-mode processes implement major functions such as file systems, network interfaces, etc.
Exokernels communicate efficiently by normal subroutine calls. The hardware and all the software in the system are available to and extensible by application programmers.
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A monolithic kernel is a relatively large kernel with sophisticated capabilities adapted to suit an embedded environment. This gives programmers an environment similar to a desktop operating system like Linux or Microsoft Windows, and is therefore very productive for development. On 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 are embedded Linux, VXWorks and Windows 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.
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In addition to the core operating system, many embedded systems have additional upper-layer software components. These components include networking protocol stacks like CAN, TCP/IP, FTP, HTTP, and HTTPS, and storage capabilities like FAT and flash memory management systems. If the embedded device has audio and video capabilities, then the appropriate drivers and codecs will be present in the system. In the case of the monolithic kernels, many of these software layers may be included in the kernel. In the RTOS category, the availability of additional software components depends upon the commercial offering.
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In the automotive sector, AUTOSAR is a standard architecture for embedded software.
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For more details of MicroVGA see this PDF
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