Embedded System Design:
A Unified Hardware/Software
Approach
Frank Vahid and Tony Givargis
Department of Computer Science and Engineering
University of California
Riverside, CA 92521
vahid@cs.ucr.edu
http://www.cs.ucr.edu/~vahid
Draft version, Fall 1999
Copyright © 1999, Frank Vahid and Tony Givargis
Preface
This book introduces embedded system design using a modern approach. Modern
design requires a designer to have a unified view of software and hardware, seeing them
not as completely different domains, but rather as two implementation options along a
continuum of options varying in their design metrics (cost, performance, power,
flexibility, etc.).
Three important trends have made such a unified view possible. First, integrated
circuit (IC) capacities have increased to the point that both software processors and
custom hardware processors now commonly coexist on a single IC. Second, quality-
compiler availability and average program sizes have increased to the point that C
compilers (and even C++ or in some cases Java) have become commonplace in
embedded systems. Third, synthesis technology has advanced to the point that synthesis
tools have become commonplace in the design of digital hardware. Such tools achieve
nearly the same for hardware design as compilers achieve in software design: they allow
the designer to describe desired processing in a high-level programming language, and
they then automatically generate an efficient (in this case custom-hardware) processor
implementation. The first trend makes the past separation of software and hardware
design nearly impossible. Fortunately, the second and third trends enable their unified
design, by turning embedded system design, at its highest level, into the problem of
selecting (for software), designing (for hardware), and integrating processors.
ESD focuses on design principles, breaking from the traditional book that focuses
on the details a particular microprocessor and its assembly-language programming. While
stressing a processor-independent high-level language approach to programming of
embedded systems, it still covers enough assembly language programming to enable
programming of device drivers. Such processor-independence is possible because of
compiler availability, as well as the fact that integrated development environments
(IDE’s) now commonly support a variety of processor targets, making such independence
even more attractive to instructors as well as designers. However, these developments
don’t entirely eliminate the need for some processor-specific knowledge. Thus, a course
with a hands-on lab may supplement this book with a processor-specific databook and/or
a compiler manual (both are typically very low cost or even free), or one of many
commonly available "extended databook" processor- specific textbooks.
ESD describes not only the programming of microprocessors, but also the design of
custom-hardware processors (i.e., digital design). Coverage of this topic is made possible
by the above-mentioned elimination of a detailed processor architecture study. While
other books often have a review of digital design techniques, ESD uses the new top-down
approach to custom-hardware design, describing simple steps for converting high-level
program code into digital hardware. These steps build on the trend of digital design books
of introducing synthesis into an undergraduate curriculum (e.g., books by Roth, Gajski,
and Katz). This book assists designers to become users of synthesis. Using a draft of
ESD, we have at UCR successfully taught both programming of embedded
microprocessors, design of custom-hardware processors, and integration of the two, in a
one-quarter course having a lab, though a semester or even two quarters would be
preferred. However, instructors who do not wish to focus on synthesis will find that the
top-down approach covered still provides the important unified view of hardware and
software.
ESD includes coverage of some additional important topics. First, while the need
for knowledge specific to a microprocessor’s internals is decreasing, the need for
knowledge of interfacing processors is increasing. Therefore, ESD not only includes a
chapter on interfacing, but also includes another chapter describing interfacing protocols
common in embedded systems, like CAN, I2C, ISA, PCI, and Firewire. Second, while
high-level programming languages greatly improve our ability to describe complex
behavior, several widely accepted computation models can improve that ability even
further. Thus, ESD includes chapters on advanced computation models, including state
machines and their extensions (including Statecharts), and concurrent programming
models. Third, an extremely common subset of embedded systems is control systems.
ESD includes a chapter that introduces control systems in a manner that enables the
reader to recognize open and closed-loop control systems, to use simple PID and fuzzy
controllers, and to be aware that a rich theory exists that can be drawn upon for design of
such systems. Finally, ESD includes a chapter on design methodology, including
discussion of hardware/software codesign, a user’s introduction to synthesis (from
behavioral down to logic levels), and the major trend towards Intellectual Property (IP)
based design.
Additional materials: A web page will be established to be used in conjunction with
the book. A set of slides will be available for lecture presentations. Also available for
use with the book will be a simulatable and synthesizable VHDL "reference design,"
consisting of a simple version of a MIPS processor, memory, BIOS, DMA controller,
UART, parallel port, and an input device (currently a CCD preprocessor), and optionally
a cache, two-level bus architecture, a bus bridge, and an 8051 microcontroller. We have
already developed a version of this reference design at UCR. This design can be used in
labs that have the ability to simulate and/or synthesize VHDL descriptions. There are
numerous possible uses depending on the course focus, ranging from simulation to see
first-hand how various components work in a system (e.g., DMA, interrupt processing,
arbitration, etc.), to synthesis of working FPGA system prototypes.
Instructors will likely want to have a prototyping environment consisting of a
microprocessor development board and/or in-circuit emulator, and perhaps an FPGA
development board. These environments vary tremendously among universities.
However, we will make the details of our environments and lab projects available on the
web page. Again, these have already been developed.
Chapter 1: Introduction
Embedded System Design, Vahid/Givargis Last update: 09/27/99 2:51 PM
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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.
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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.
