Chapter 1: Introduction
Embedded System Design, Vahid/Givargis Last update: 09/27/99 2:51 PM
Chapter 1 Introduction
1.1 Embedded systems overview
Computing systems are everywhere. It’s probably no surprise that millions of
computing systems are built every year destined for desktop computers (Personal
Computers, or PC’s), workstations, mainframes and servers. What may be surprising is
that billions of computing systems are built every year for a very different purpose: they
are embedded within larger electronic devices, repeatedly carrying out a particular
function, often going completely unrecognized by the device’s user. Creating a precise
definition of such embedded computing systems, or simply embedded systems, is not an
easy task. We might try the following definition: An embedded system is nearly any
computing system other than a desktop, laptop, or mainframe computer. That definition
isn’t perfect, but it may be as close as we’ll get. We can better understand such systems
by examining common examples and common characteristics. Such examination will
reveal major challenges facing designers of such systems.
Embedded systems are found in a variety of common electronic devices, such as: (a)
consumer electronics -- cell phones, pagers, digital cameras, camcorders, videocassette
recorders, portable video games, calculators, and personal digital assistants; (b) home
appliances -- microwave ovens, answering machines, thermostat, home security, washing
machines, and lighting systems; (c) office automation -- fax machines, copiers, printers,
and scanners; (d) business equipment -- cash registers, curbside check-in, alarm systems,
card readers, product scanners, and automated teller machines; (e) automobiles --
transmission control, cruise control, fuel injection, anti-lock brakes, and active
suspension. One might say that nearly any device that runs on electricity either already
has, or will soon have, a computing system embedded within it. While about 40% of
American households had a desktop computer in 1994, each household had an average of
more than 30 embedded computers, with that number expected to rise into the hundreds
by the year 2000. The electronics in an average car cost $1237 in 1995, and may cost
$2125 by 2000. Several billion embedded microprocessor units were sold annually in
recent years, compared to a few hundred million desktop microprocessor units.
Embedded systems have several common characteristics:
1) Single-functioned: An embedded system usually executes only one
program, repeatedly. For example, a pager is always a pager. In contrast, a
desktop system executes a variety of programs, like spreadsheets, word
processors, and video games, with new programs added frequently.
1
2) Tightly constrained: All computing systems have constraints on design
metrics, but those on embedded systems can be especially tight. A design
metric is a measure of an implementation’s features, such as cost, size,
performance, and power. Embedded systems often must cost just a few
dollars, must be sized to fit on a single chip, must perform fast enough to
process data in real-time, and must consume minimum power to extend
battery life or prevent the necessity of a cooling fan.
There are some exceptions. One is the case where an embedded system’s program is
updated with a newer program version. For example, some cell phones can be updated in
such a manner. A second is the case where several programs are swapped in and out of a
system due to size limitations. For example, some missiles run one program while in
cruise mode, then load a second program for locking onto a target.
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