Embedded system
An embedded system is a
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
Embedded systems range from those low in complexity, with a single microcontroller chip, to very high with multiple units,
History
Background
The origins of the microprocessor and the microcontroller can be traced back to the
The first multi-chip microprocessors, the
Development
One of the first recognizably modern embedded systems was the
An early mass-produced embedded system was the
Since these early applications in the 1960s, embedded systems have come down in price and there has been a dramatic rise in processing power and functionality. An early microprocessor, the Intel 4004 (released in 1971), was designed for calculators and other small systems but still required external memory and support chips. By the early 1980s, 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.
Applications
Embedded systems are commonly found in consumer, industrial, automotive, home appliances, medical, telecommunication, commercial, aerospace and military applications.
Transportation systems from flight to automobiles increasingly use embedded systems. New airplanes contain advanced
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
Characteristics
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
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.
User interfaces
Embedded systems range from
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.
Processors in embedded systems
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.
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
However, most ready-made embedded systems boards are not PC-centered and do not use the
One common design style uses a small system module, perhaps the size of a business card, holding high density
ASIC and FPGA SoC solutions
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.
Peripherals
Embedded systems talk with the outside world via peripherals, such as:
- , etc.
- SPI, SSC and ESSI (Enhanced Synchronous Serial Interface)
- Universal Serial Bus(USB)
- Media cards (SD cards, CompactFlash, etc.)
- WiFi, etc.
- PROFIBUS, etc.
- Timers: Phase-locked loops, programmable interval timers
- General Purpose Input/Output(GPIO)
- Analog-to-digital and digital-to-analog converters
- Debugging: JTAG, In-system programming, background debug mode interface port, BITP, and DB9 ports.
Tools
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:
- In circuit debuggers or emulators (see next section).
- Utilities to add a checksum or CRC to a program, so the embedded system can check if the program is valid.
- For systems using computational notebookto simulate the mathematics.
- System-level modeling and simulation tools help designers to construct simulation models of a system with hardware components such as memories, DMA, interfaces, buses and software behavior flow as a state diagram or flow diagram using configurable library blocks. Simulation is conducted to select the right components by performing power vs. performance trade-offs, reliability analysis and bottleneck analysis. Typical reports that help a designer to make architecture decisions include application latency, device throughput, device utilization, power consumption of the full system as well as device-level power consumption.
- A model-based development tool creates and simulates graphical data flow and UML state chart diagrams of components like digital filters, motor controllers, communication protocol decoding and multi-rate tasks.
- 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 as Forth or Basic.
- Another alternative is to add a RTOS or embedded operating system
- Modeling and code generating tools often based on state machines
Software tools can come from several sources:
- Software companies that specialize in the embedded market
- Ported from the GNU 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,
Debugging
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 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)
- Software-only debuggers have the benefit that they do not need any hardware modification but have to carefully control what they record in order to conserve time and storage space.[10]
- External debugging using logging or serial port output to trace operation using either a monitor in flash or using a debug server like the Remedy Debugger that 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.[11] 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. The downsides are expense and slow operation, in some cases up to 100 times slower than the final system.
- For SoC designs, the typical approach is to verify and debug the design on an FPGA prototype board. Tools such as Certus[12] 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
Tracing
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.
Reliability
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:
- 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. Reduced functionality in the event of failure may be intolerable. 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.
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:
- watchdog timer that resets and restarts the system unless the software periodically notifies the watchdog subsystems
- Designing with a trusted computing base (TCB) architecture ensures a highly secure and reliable system environment[14]
- A hypervisor designed for embedded systems 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.[15] This encapsulation keeps faults from propagating from one subsystem to another, thereby improving reliability. This may also allow a subsystem to be automatically shut down and restarted on fault detection.
- Immunity-aware programming can help engineers produce more reliable embedded systems code.[16][17] Guidelines and coding rules such as MISRA C/C++ aim to assist developers produce reliable, portable firmware in a number of different ways: typically by advising or mandating against coding practices which may lead to run-time errors (memory leaks, invalid pointer uses), use of run-time checks and exception handling (range/sanity checks, divide-by-zero and buffer index validity checks, default cases in logic checks), loop bounding, production of human-readable, well commented and well structured code, and avoiding language ambiguities which may lead to compiler-induced inconsistencies or side-effects (expression evaluation ordering, recursion, certain types of macro). These rules can often be used in conjunction with code static checkers or bounded model checking for functional verification purposes, and also assist in determination of code timing properties.[16]
High vs. low volume
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.
Embedded software architectures
In 1978 National Electrical Manufacturers Association released ICS 3-1978, 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.
Simple control loop
In this design, the software simply has a
Interrupt-controlled system
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.
Cooperative multitasking
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.
Preemptive multitasking or multi-threading
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
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,
Microkernels and exokernels
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.
Monolithic kernels
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
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.
Additional software components
In addition to the core operating system, many embedded systems have additional upper-layer software components. These components include networking protocol stacks like
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.Domain-specific architectures
In the automotive sector, AUTOSAR is a standard architecture for embedded software.
See also
Notes
References
- ^ a b Michael Barr. "Embedded Systems Glossary". Neutrino Technical Library. Retrieved 2007-04-21.
- ISBN 978-0-7506-5546-0.based system that is built to control a function or a range of functions.
An embedded system is a microprocessor
- ^ ISBN 978-0-596-00983-0.
- ^ Barr, Michael (1 August 2009). "Real men program in C". Embedded Systems Design. TechInsights (United Business Media). p. 2. Retrieved 2009-12-23.
- S2CID 32003640. Retrieved 13 October 2019.
- ^ "1971: Microprocessor Integrates CPU Function onto a Single Chip". The Silicon Engine. Computer History Museum. Retrieved 22 July 2019.
- ^ "Electronic Frontier Foundation". Electronic Frontier Foundation.
- ^ Embedded Systems Dell OEM Solutions | Dell Archived 2013-01-27 at the Wayback Machine. Content.dell.com (2011-01-04). Retrieved on 2013-02-06.
- ^ David Carey (2008-04-22). "Under the Hood: Robot Guitar embeds autotuning". Embedded Systems Design. Archived from the original on 2008-07-08.
- S2CID 10120929.
- S2CID 14769602.
- ^ "Tektronix Shakes Up Prototyping, Embedded Instrumentation Boosts Boards to Emulator Status". Electronic Engineering Journal. 2012-10-30. Retrieved 2012-10-30.
- ISBN 978-3-642-16611-2, retrieved 2022-08-16
- ^ Heiser, Gernot (December 2007). "Your System is secure? Prove it!" (PDF). ;login:. 2 (6): 35–8. Archived (PDF) from the original on 2014-11-29.
- S2CID 17466572. Retrieved 2 February 2018.
- ^ S2CID 14163138.
- ^ Motor Industry Software Reliability Association. "MISRA C:2012 Third Edition, First Revision". Retrieved 2022-02-03.
- ^ "FAQs: Programmable Controllers" (PDF). Retrieved 2020-01-10.
- ^ "Working across Multiple Embedded Platforms" (PDF). clarinox. Archived (PDF) from the original on 2011-02-19. Retrieved 2010-08-17.
Further reading
- John Catsoulis (May 2005). Designing Embedded Hardware, 2nd Edition. O'Reilly. ISBN 0-596-00755-8.
- James M. Conrad; Alexander G. Dean (September 2011). Embedded Systems, An Introduction Using the Renesas RX62N Microcontroller. Micrium. ISBN 978-1935-7729-96.
- Klaus Elk (August 2016). Embedded Software Development for the Internet Of Things, The Basics, The Technologies and Best Practices. CreateSpace Independent Publishing Platform. ISBN 978-1534602533.
External links
- Embedded Systems course with mbed YouTube, ongoing from 2015
- Trends in Cyber Security and Embedded Systems Dan Geer, November 2013
- Modern Embedded Systems Programming Video Course YouTube, ongoing from 2013
- Embedded Systems Week (ESWEEK) yearly event with conferences, workshops and tutorials covering all aspects of embedded systems and software
- Workshop on Embedded and Cyber-Physical Systems Education at the Wayback Machine (archived 2018-02-11), workshop covering educational aspects of embedded systems