Embedded system - Wikipedia

Computer system with a dedicated function

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]

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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.

See also: Microprocessor chronology

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]

One of the first recognizably modern embedded systems was the Apollo Guidance Computer,[7] 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.

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.[9]

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.

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.[10] Similarly, an embedded system in an automobile provides a specific function as a subsystem of the car itself.

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.

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.

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.

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.

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.

Embedded systems talk with the outside world via peripherals, such as:

• Serial communication interfaces (SCI): RS-232, RS-422, RS-485, etc.
• Synchronous Serial Interface: I2C, SPI, SSC and ESSI (Enhanced Synchronous Serial Interface)
• Universal Serial Bus (USB)
• Media cards (SD cards, CompactFlash, etc.)
• Network interface controller: Ethernet, WiFi, etc.
• Fieldbuses: CAN bus, LIN-Bus, 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.

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 digital signal processing, developers may use a computational notebook to simulate the mathematics.
• System-level modeling and simulation tools help designers to construct simulation models of a system with hardware components such as processors, 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

Embedded software often requires a variety of development tools, including programming languages such as C++, Rust, or Python, and frameworks like Qt for graphical interfaces. These tools enable developers to create efficient, scalable, and feature-rich applications tailored to the specific requirements of embedded systems. The choice of tools is driven by factors such as real-time performance, integration with hardware, or energy efficiency.

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.

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:

• 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.[11]
• 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.[12] 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[13] 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.

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.[14] 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.

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: 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[15]
• 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.[16] 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.[17][18] 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.[17]

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.

Main article: Embedded software

In National Electrical Manufacturers Association released ICS 3-, a standard for programmable microcontrollers,[19] 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.

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.

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.

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.[20]

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.

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.

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.

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.

In the automotive sector, AUTOSAR is a standard architecture for embedded software.

• Electronics portal

• John Catsoulis (May ). Designing Embedded Hardware, 2nd Edition. O'Reilly. ISBN 0-596--8.
• James M. Conrad; Alexander G. Dean (September ). Embedded Systems, An Introduction Using the Renesas RX62N Microcontroller. Micrium. ISBN 978---96.
• Klaus Elk (August ). Embedded Software Development for the Internet Of Things, The Basics, The Technologies and Best Practices. CreateSpace Independent Publishing Platform. ISBN 978-.

Computer-on-modules are world-leading platforms for embedded system designs. What makes them so attractive and what are their limitations?

Studies from IHS Markit state that computer-on-modules are leading the global ranking of embedded form factors followed by standalone boards and VME/VPX solutions. They also forecast a growth of 8.6% CAGR during the period –, which is impressive as market-leading technology is generally well established and market volume tends to be stable rather than dynamic. Similar studies from Research and Markets paint a much healthier growth perspective, forecasting that the global computer-on-module market will be growing at a CAGR of 17.97% during the period –.

The large difference between these two forecasts may be caused by the highly uncertain market dynamics in the IoT segment, where these modules will get massively deployed. IHS Markit identifies the needs of industrial automation and Industry 4.0 as a major driver of growth in coming decades. So from a bird’s-eye view of the market perspectives, there is no doubt that computer-on-modules are suitable candidates to evaluate for embedded system designs. But what makes them so attractive?

Made for customisation

Computer-on-modules are building blocks for custom system designs. Custom designs are quite often demanded in the embedded computing area as off-the-shelf motherboards cannot be used for all embedded applications. The available space may not be sufficient. Interface demands are almost always individual in terms of number, configuration and location on the boards. Also, a motherboard with expansion cards may just not offer the required resistance against mechanical or thermal stress.

All these individual demands lead to the question: shall I build my own design from scratch with all efforts and costs involved, or are there other options available that can help me design my dedicated system faster and more efficiently? Computer-on-modules were invented exactly to help with this ‘build or buy’ question and the intention to simplify the use of embedded processor technologies in customised designs.

Application-ready super components

Computer-on-modules are application-ready super components that offer engineers high design efficiency. One benefit for purchase departments is the fact that the bill of material is reduced from many components to a single module for the processing core — but this is only the smaller part of the efficiency gain. More important are the reduced efforts required to design-in the processor, RAM and high-speed interfaces on the one hand, and to build the entire board support package with all the necessary drivers, libraries and APIs on the other. All this work is already done and modules can be deployed nearly as simply as a new processor on a motherboard — but there is a huge difference between the switch of a processor and a computer-on-module.

Nearly endless scalability

Computer-on-modules offer nearly endless scalability. While a processor change can only be executed with pin-compatible processors that are generally only available within a certain processor generation, computer-on-modules can basically host all processors from all leading embedded processor vendors. One example is the update from the 5th generation of Intel Core processors to the 6th generation, where the grid array and memory interface changed. When leveraging a customised board, designers would have to redesign their PCB. With computer-on-modules, a switch between processor generations and vendors is much simpler and always possible. A new product generation can be launched just by switching the module.

Modules also make a design vendor-independent, with the benefit of higher design security. Another advantage of this scalability feature is that it extends the long-term availability of applications as when the seven- or 10-year product life cycle of an embedded processor ends, a successor is often available that can be used as a retrofit. If the design is based on modules, again only a switch of the module is required.

The benefits of standardisation

But this scalability can only be secured by interface standardisation. Computer-on-modules achieve this by standardising the footprints as well as the interface to the custom-designed carrier boards of the modules. While such standardisation can be a limiting factor that makes it necessary to have several specifications available to target all major applications, the benefits are tremendous.

Standardisation leads to highest design security as designers can rely on the future availability of modules with the same interfaces. They can also develop second source strategies and are not dependent on a single vendor. This benefits not only the design security but also provides commercial advantages due to competitive pricing. There is also greater room for module vendors to offer more services in an attempt to separate themselves from competitors by improved support of customers’ demands.

Standardisation further delivers the capabilities to offer a broad ecosystem of commercially available accessories, ranging from heat spreaders and carrier boards to cable sets and housings. This makes it easy to purchase components from third parties so that NRE costs are reduced to a minimum. Finally, a large community of designers working with the form factor ensures continuous standard improvements.

Suitable where no other form factor fits

Having said all this, computer-on-modules are really only suitable if no other embedded form factor fits. Engineers consequently need to check the specifications and market trends of other embedded form factors before choosing a module approach. As the forecast from IHS indicates, checking the availability of standalone boards which directly fit the application is most important.

The relevant form factors in this growth cluster are the Mini-ITX and Pico-ITX boards, as well as the new eNUC standard, as they offer small form factors perfectly suited for space-constrained embedded system designs. In the market segment of passive backplane-based systems, only VME/VPX shows good growth perspectives — due to intensified spending in the military market — while CompactPCI and xTCA technologies are declining.

Image credit: IHS Markit.

Unsuitable for ultrahigh-volume productions

Engineers also need to check whether a full custom design might fit better in the end. This is always the case in ultrahigh-volume productions, where every single component is a cost factor to be considered for economising. While the connector of a module may cost only $1, when you’ve got 10 pieces this adds up to $10 and the mounting of the module is a cost factor too. So when it comes to very high-volume productions, the breakeven point between a COM/carrier concept as opposed to a full custom design needs to be determined.

Calculating this breakeven point is complex, as R&D costs and investments in future upgrades also need to be taken into account. Module vendors can help OEMs with these calculations, as in most cases they also offer embedded design and manufacturing services for full custom boards where they can often re-use the layouts of the carrier board designs manufactured for the evaluation of the boards.

Spoilt for choice

After having evaluated these options and finding that a computer-on-module approach fits best, engineers need to evaluate the right computer-on-module standard as a final step. Today’s state-of-the-art technologies include the specifications from two worldwide standardisation bodies: the PCI Industrial Computer Manufacturers Group (PICMG) hosting the COM Express standard and the Standardization Group for Embedded Technologies e.V. (SGET), which is responsible for Qseven and SMARC.

COM Express

The COM Express standard defines a family of different module sizes and pinout types covering a broad range of designs from low-power small form factor devices up to powerful embedded servers. COM Express sizes include:

• Mini (84 x 55 mm)
• Basic (95 x 125 mm)
• Compact (95 x 95 mm)
• Extended (110 x 155 mm)

COM Express footprints.

COM Express Type 7

PICMG’s COM Express Type 7 specification is tailored for modular server designs, which are being deployed at the edge of the IoT and Industry 4.0 applications as cloud and fog servers, or in cloudlets at the edge of the carriers’ base stations for high-bandwidth mobile communications. What is most interesting from a feature set point of view is the support of up to 4x 10 GbE bandwidth and up to 32x high-speed PCIe for high-performance storage, and dedicated interfaces supported by 440 signal pins to the carrier board. Target processors that can be found on the basic sized 95 x 125 mm modules include the Intel Xeon D processors and the upcoming successors from both x86 server processor vendors, Intel and AMD. Larger modules are possible as well, as COM Express already specifies the Extended format measuring 110 x 155 mm.

The COM Express Type 7 server-on-modules provide up to 4x 10 Gbit Ethernet and up to 32 PCIe Lanes. The conga-B7XD server-on-module integrates latest Intel Xeon D processors with up to 16 cores and 48 GB of DDR4 RAM.

COM Express Type 6

The established PICMG COM Express Type 6 specification is state of the art for the high-end sector of embedded computer systems with implemented processors ranging from Intel Core, Pentium and Celeron to the AMD Embedded R-Series. These modules measure 95 x 125 mm (Basic) or 95 x 95 mm (Compact), provide 440 pins to the carrier board and offer a comprehensive set of state-of-the-art computer interfaces with everything needed to build powerful PLCs, HMIs, shop floor systems or SCADA workstations in control rooms. Further application areas are high-end digital signage systems, high-end gaming machines and complex kiosk systems.

COM Express Type 6 modules like the conga-TC-175 and the conga-TS175 with Intel Core processors provide PC-like interfaces including multiple graphics, USB 3.0 and 2.0, as well as PCIe outputs plus many typical embedded I/Os.

COM Express Type 10

PICMG’s small form factor COM Express Type 10 rounds off the set of COM Express specifications. It comes with the credit card sized Mini form factor. These modules measure only 55 x 84 mm, offer 220 pins and are dedicated for low-power x86 SoC processors such as Intel Atom and Celeron as well as AMD G-Series processors. Thanks to the unified connector technology and design guides used within the entire PICMG COM Express ecosystem, developers can re-use as many features as possible. Designers have one standard they can leverage to scale their designs on the basis of COM Express, from Mini Type 10 modules with Intel Atom processors up to Intel Xeon D processors for the server segment.

The conga-MA5 with latest low-power Intel Atom, Celeron and Pentium processors in the COM Express Mini footprint with Type 10 pin-out extends the COM Express scalability to small form factor designs.

Qseven and SMARC

Engineers that are targeting not only x86 but also ARM-based designs are best served with Qseven or SMARC 2.0 modules as they incorporate both processor architectures. The difference between Qseven and SMARC 2.0 can quite easily be explained. On the connector side, Qseven offers 230 pins and SMARC 2.0 offers 314 pins. SMARC is more orientated towards feature rich multimedia applications, whereas Qseven offers more I/Os as required by the deeply embedded and industrial arena.

All the other benefits are comparable. Both standards enable slimmer designs compared to COM Express because of their flat edge connectors. Both have reliable connector vendors: the Qseven connector is currently supported by three and the SMARC 2.0 connector by two vendors. So for all those who have criticised Qseven in the past for only having one connector vendor, it needs to be underlined that this vendor bottleneck has now not only disappeared but changed to a slight advantage compared to SMARC 2.0.

The difference in the number of interfaces between Qseven and SMARC 2.0 is also kind of a price indicator: Qseven is designed for less complex designs and SMARC for the high-end of small form factor applications that demand credit card-sized modules. In general, any decision therefore depends on what the task of an embedded system will be.

SMARC modules like the conga-SA5 with Intel Atom, Celeron and Pentium processors target feature-rich multimedia applications, whereas Qseven is intended for the deeply embedded and industrial arena. Both form factors can host x86 as well ARM processor technology.

Conclusion

The benefits of computer-on-modules are so substantial that a majority of embedded system designs are already using these application-ready building blocks. As the number of IoT and Industry 4.0 applications multiplies, many new designs are forecast to be also based on computer-on-modules and the new class of server-on-modules for edge computing. Identifying the best form factor is the next major step within the design evaluation process where module vendors can help. As long as they offer all the relevant form factors, they can provide better consultancy as well as better options to migrate from one form factor to the other.

When choosing the right vendor, it is key to have a look at the BSPs, firmware and communication middleware, as they are getting more and more important in a connected world. This does not mean that the vendor should complement its offerings with an entire cloud for the system because it will never meet the needs of a customer entirely. It is more important to have a closer look at what is offered on the board and module level itself. For example, is the board management controller proprietary? Then take care as it could prove to be a dead end. Better to choose open, non-proprietary APIs because openness and standards are the fundament for most efficient and simplified re-use of existing engineering efforts. Check that integration support is offered for ARM and x86, because it is better to get one engineer who supports both architectures for a unified product family instead of two different engineers with two different product lines. This also requires unified APIs.

Finally, check the provided documentation. It is better to have more pages of content instead of only the bare minimum. And think also about relying on local manufacturing capacities wherever you or your customer reside. This will not only allow you or your customer to buy local but can also help with potential government trade restrictions. Fabless board-level vendors such as congatec, with subsidiaries all over the world, can offer you all these advantages.

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