Section 1: Fundamentals of High-Performance Embedded Systems
This part introduces the basic concepts of embedded systems, real-time computing, and Field Programmable Gate Array (FPGA) devices. It provides a high-level overview of topics that will be covered in detail in later chapters.
This part of the book comprises the following chapters:
- Chapter 1, Architecting High-Performance Embedded Systems
- Chapter 2, Sensing the World
- Chapter 3, Operating in Real Time
Chapter 1: Architecting High-Performance Embedded Systems
This chapter introduces the elements of embedded system architectures and discusses some key system features that are common across a wide variety of embedded applications. An embedded system generally includes at least one microcontroller or microprocessor, sensors, actuators, a power source, and, in many cases, one or more network interfaces. The chapter continues with an exploration of the relationship between embedded systems and the Internet of Things (IoT).
This chapter emphasizes the necessity for many types of embedded systems to function in a real-time manner and presents the basic embedded system operating sequence of reading from input devices, computing outputs, and updating output devices in a repetitive manner while remaining synchronized with the passage of time.
The chapter concludes with an introduction to digital logic and the Field-Programmable Gate Array (FPGA), and identifies the design space within the spectrum of embedded systems most appropriately addressed by these high-performance devices.
After completing this chapter, you will have a broad understanding of the components that make up embedded systems and the relationship of embedded systems to the IoT. You will know why many embedded systems must operate in synchronization with real time and will understand the basic structure of FPGAs and how they can be employed to implement high-performance embedded systems.
We will cover the following topics in this chapter:
- Elements of embedded systems
- The Internet of Things
- Operating in real time
- FPGAs in embedded systems
Technical requirements
The files for this chapter are available at https://github.com/PacktPublishing/Architecting-High-Performance-Embedded-Systems.
Elements of embedded systems
Embedded systems are everywhere. Almost any electrical device you interact with that is more complicated than a simple light switch contains a digital processor that reads input data from its environment, executes a computational algorithm, and generates some kind of output that interacts with the environment.
From the moment you open your eyes in the morning (in response to an alarm produced by a digital device), to brushing your teeth (with an electric toothbrush that contains a digital processor), to toasting a breakfast bagel (in a digitally controlled toaster oven), to disabling your (digital) home alarm system, you interact with embedded devices. Throughout the day, you provide input to, and receive output from, many other devices, such as television remote controls, traffic signals, and railroad crossings. Highly digitized transportation systems, including automobiles, airplanes, and passenger ferries, each contain dozens, if not hundreds, of embedded processors that manage drive train operation, oversee safety features, maintain a comfortable climate, and provide entertainment for the humans they carry.
Let's take a moment to clarify the sometimes-murky dividing line separating embedded systems from general-purpose computing devices. The attribute that defines an embedded computing system is the integration of digital processing within a device that has some larger purpose beyond mere computing. Devices that do not contain any type of digital processing are not embedded systems. For example, an electric toothbrush that contains only a battery and a motor controlled by an on-off switch is not an embedded system. A toothbrush containing a microcontroller that illuminates a red light when you press down too hard while brushing is an embedded system.
A desktop computer, even though it is capable of performing many tasks, and can be enhanced through the addition of a wide variety of peripherals, is just a computer. An automobile, on the other hand, has as its primary purpose the transportation of passengers. In performing this function, it relies on a variety of subsystems containing embedded processing. Automobiles are embedded systems. Personal computers are not.
A smartphone is more difficult to clearly categorize in terms of membership in the set of embedded systems. When in use as a telephone, it is clearly performing a function consistent with the definition of an embedded system. When using it as a web browser, though, it more closely resembles a small general-purpose computer. Clearly, it is not always possible to definitively determine whether a device is an embedded system.
It is helpful to understand differences in the operating environment of general-purpose computers in comparison to embedded devices. Personal computers and enterprise servers tend to work best in climate-controlled indoor settings. Embedded devices such as those in automobiles are often exposed to far more rugged conditions, including the full effects of rain, snow, wind, dust, and heat.
A large percentage of embedded devices lack any sort of active cooling system (which is standard in personal computers and server computers) and must ensure their internal components remain at safe operating temperatures regardless of external conditions.
Embedded systems, whether they are relatively simple devices or highly complex systems, are typically composed of the following elements.
Power source
All electronic digital devices require some a of power. Most commonly, embedded systems are powered by utility electrical power, batteries, or by the host system in which the device operates. For example, an automobile taillight assembly containing a processor and a CAN bus communication interface is powered by 12 volts Direct Current (DC) provided by the car's electrical system.
It is also possible to power embedded devices from rechargeable batteries connected to solar panels that allow the device to continue operation at nighttime and on cloudy days, or even by harvesting energy from the environment. A self-winding wristwatch uses energy harvested from arm motion to generate mechanical or electrical power. Safety- and security-critical embedded systems often use utility power as the primary power source while also providing batteries as backup power to enable operation during power outages.
Time base
Embedded systems generally require some means of tracking the progress of time, also known as wall clock time, both in the short term (for durations of microseconds and milliseconds) and in the long term, keeping track of the date and time of day. Most commonly, a primary system clock signal is generated using a crystal oscillator or a Microelectromechanical System (MEMS) oscillator that produces an output frequency of a few megahertz.
A crystal oscillator amplifies the resonant vibration of a physical crystal, typically made of quartz, to generate a square wave electrical signal using the piezoelectric effect. A MEMS oscillator contains a vibrating mechanical structure that produces an electrical output using electrostatic transduction.
Once set to the correct time, a clock driven by a crystal oscillator or a MEMS oscillator will exhibit small errors in frequency (typically 1-100 parts per million) that accumulate over periods of days and weeks to gradually drift by seconds and then minutes away ...
