MTE 325 - EMBEDDED
SYSTEMS
allyson giannikouris*, p.eng.
Revised Spring 2024
Version 1.1
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embedded systems
Embedded systems are everywhere. You probably interacted with several before
you left the house this morning. Rarely do we stop to think about what exactly
an embedded system is. There is also some ambiguity in definitions depending
on the source you use. For the sake of this course, the definitions presented here
will be used.
Think About
What is an embedded system?
* Dept. of Mechanical and Mechatronics Eng., University of Waterloo
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1.1 Introduction to Embedded Systems
Embedded system: A special-purpose computer system designed to perform a
task without the user’s knowledge of its existence. The user may provide input
to the embedded system via controls and sensors but the user need not be aware
of the presence of the embedded system.
Figure 1 shows some examples of embedded systems. Most people would
readily agree that the digital camera fits the definition, but what about the cell
phone? Is it still an embedded system by the definition above? This is a tricky
one and highlights that there aren’t always clear lines on what is and is not an
embedded system. 15 years ago, the answer would have been a clear yes that a
cell phone is an embedded system. These days its harder to argue that the average
user doesn’t recognize their phone as a computer.
Image credit: Uberprutser CC-BY-SA 3.0
Image Credit: Senado Federal CC-BY-2.0
Figure 1: Examples of embedded systems, a digital camera on the left and cell phones on
the right
Think About
What embedded systems do you interact with on a daily basis?
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1.2 Embedded System Design
Embedded systems come in all shapes and sizes. Simple embedded systems can
be constructed out of electronics without the need for a processor or software,
however there will be state (memory) of some kind. Complex embedded systems
incorporate one or more processors with sophisticated control software.
There is no standard, widely accepted process for embedded system design.
Rather, there are some general building blocks to be considered. The first step in
the process is the identification of the problem and development of requirements
and specifications. This is a whole design process in and of itself, which is beyond
the scope of this course.
Once the requirements and specifications are knows, the primary hardware
components, such as the microcontroller to be used and/or a development board
and required peripherals are selected. Now that the components are knows, hardware design can be completed. This includes selecting interfaces and wiring the
hardware components together. For prototyping this is often done using development kits and breadboards, but for production may include designing custom
printed circuit boards (PCBs).
The software development may be done at any point after component selection. In an ideal world, hardware / software codesign would be used, allowing
the hardware to be optimized on the fly. True codesign means simultaneously
designing hardware and software components of a combined hardware/software
system. As it stands today, field programmable gate array (FPGA)-based development is as close as we get. For microcontroller based designs, the processor may
have some pin-compatible options in the same family, but major changes are difficult once software development has begun. In most cases, the major hardware
components are selected before software development begins.
While the process generally flows from left to right as shown in Figure 2, it
is also cyclic. There will inevitably be issues that are found or changes to the
requirements and specifications during the hardware and software development
that require revisiting the earlier decisions and iterating the design.
The complexity of embedded system design can be very deceptive. Things that
seem simple at first rarely are. While the purpose of the system and intended
behaviour are often conceptually simple, actually implementing them and understanding the finer points of how the entities are communicating tends to be far
more complicated. To use an analogy, the idea that you push a button or turn a
key and the car starts is simple enough, but the details of all the steps between
your action and the car starting are far more complex.
Getting an embedded system working is relatively easy, especially since the
advent of ecosystems like Arduino boards that have significantly lowered the barriers to entry in programming them. That said, great embedded systems designs
require engineering judgment and experience. There is a difference between be-
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Figure 2: A very high level representation of the embedded system development process.
ing able to make something work and understanding why and how it works. The
designer must often content with multiple factors, such as
• multidisciplinary design problems,
• complex device interactions, and
• unpredictable external environment.
The level of abstraction in embedded software also tends to be quite low. The
code is often tied to a specific processor or processor family, and porting to another system will require some changes to be made. If the code was written with
portability in mind, it could be as simple as changing some definitions in a file. If
the code was written for optimal performance on a given system, it may require
extensive changes before it will run on a different one.
On top of these factors, security is becoming increasingly more critical as more
and more of these systems handle private or sensitive data and communicate
over networks. These systems are also more difficult to update than software
apps, meaning reliability and robustness of the system are important factors to
consider.
1.3 Computer Technology
Concise definitions of computer hardware and computer software are needed for
meaningful discussions of embedded systems. According to the Canadian Oxford
Dictionary [1]:
Hardware 3. the mechanical or electronic components of a computer, etc.
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Software 1. the programs or other operating information used by a computer. 2.
storage media such as video cassettes, audio tapes, etc. requiring playback
on electronic equipment
The software definition encompasses both programs and media (data). While
most apps are downloaded these days, it wasn’t that long ago that they were
commonly distributed on compact disks (CDs), which by this definition would be
software.
Many years ago, Prof. Bill Bishop shared his definition with me, and it perhaps
makes the distinction easier to remember: Hardware is the part you can kick,
software is the part you wish you could kick.
1.3.1 Processor Types
Computer hardware can be broadly categorized based on the relationship between the processor and the peripherals. Once again, there are some gray areas
on where exactly some chips might fall and the definitions are not necessarily
broadly standardized. For the purposes of this course, the definitions here will
be used to facilitate discussions and provide a common reference point.
A Microprocessor consists of a processor only. There is no main memory and no
built-in support for input / output devices. The microprocessor term commonly
refers to a general-purpose Central Processing Unit (CPU). Examples include the
Intel Core i5 which is shown in Figure 3, AMD Ryzen and IBM z14. Despite the
name, these are high performance processors. Today, they commonly have multiple cores and are usually found in laptops, desktops and servers. Because they
are a standalone processor and require separate peripherals, they are typically
used with a motherboard that provides the required interfaces and memory for
the system to be functional. A system based on a microprocessor will, in general,
NOT be an embedded system.
Image Credit: Ashley Pomeroy - Own work, CC BY-SA 4.0,
https://commons.wikimedia.org/w/index.php?curid=89232962
Figure 3: The Intel Core i5 is an example of a microprocessor
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A Microcontroller is a complete computer on a single chip consisting of a processor, memory and some input / output devices. These devices are usually specified in a fairly general manner to permit reuse of the same microcontroller component in many applications. Examples include the ST Microelectronics STM32
family, Texas Instruments TMS320 and Microchip ATtiny. The block diagram for
the ATtiny 1617 microcontroller, which includes a CPU, memory, analog interfaces, digital interfaces, communication support and timers is shown in Figure 4.
This term commonly refers to a chip with a CPU that has been specialized to control the operation of a mechanical or electronic system. These tend to be small and
cost-effective, starting at a few dollars per chip. Each chip will have specialized
built-in interface support for some or all of high-speed communication, parallel
devices, serial devices, and analog devices.
Image Credit: Microchip Technology, ATtiny1617/3217 Datasheet
Figure 4: Block diagram of a Microchip microcontroller showing the CPU, memory and
peripheral interfaces available inside a single chip
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A System-on-a-Chip (SoC) is a user-designed fully-functional system implemented on a single chip. This may include processing, memory, input / output
devices and other digital logic. It can be used to implement an embedded system
or a portion of an embedded system. The difference between a microcontroller
and an SoC is that the SoC configuration is chosen by the user. Interfaces and
memory are selected from a list of available blocks as illustrated in Figure 5, then
the chip is fabricated for the user. These devices come with configuration and
fabrication costs, so they are generally only viable for higher volume or very
specialized applications where an off the shelf microcontroller doesn’t meet the
design requirements.
Typically, an SoC incorporates the following hardware components, with the
exact configuration being dependent on the application:
• Functionality similar to the microprocessor or a microcontroller defined previously. The implementation may be done in hardware or software.
• Communication port(s)
• Volatile storage (e.g., Random Access Memory ⇒ RAM )
• Non-volatile storage (e.g., Read-Only Memory ⇒ ROM )
• Other components could include: timers, parallel interfaces, analog to digital converters and pulse width modulators.
Image Credit: Cypress Semiconductor
Figure 5: An illustration of a SoC, showing the peripherals and memory being "plugged
in" to the system configuration
A System-on-a-Programmable-Chip (SoPC) is an SoC that is implemented using a high-density, reconfigurable programmable logic device (PLD) with a structure similar to that shown in Figure 6. Unlike the SoC, the user is able to reconfigure and program the chip logic themselves. These days, many SoPC chips have
either a CPU block that can be loaded to them or contain a hardwired CPU surrounded by programmable logic. Field programmable gate arrays (FPGAs) are an
example of an SoPC.
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Glossary
Image Credit: Mouser, http://ca.mouser.com/applications/programmable-logic/
Figure 6: A block diagram showing the typical structure of a SoPC device
1.4 Summary
Embedded systems are special-purpose computer systems that perform a task
without the users knowledge. They can be built using different types of hardware, although microcontrollers are the most common. The relationship between
the hardware and software development of the system has been briefly considered
and will be explored more deeply in coming chapters. The differences between
the various hardware classifications were introduced to provide an understanding of the options that are available. This course will primarily focus on microcontrollers, although many of the same ideas and concepts are relevant to other
implementation methods.
glossary
embedded system A special-purpose computer system designed to perform a
task without the user’s knowledge of its existence. The user may provide
input to the embedded system via controls and sensors but the user need
not be aware of the presence of the embedded system. 2, 3
Hardware The mechanical or electronic components of a computer etc. 4
hardware / software codesign Hardware/software codesign is the term given to
the task of simultaneously designing hardware and software components
of a combined hardware/software system. 3
Microcontroller A complete computer on a single chip consisting of a processor
memory and some input / output devices. 6
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references
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Microprocessor A microprocessor consists of a processor only (no main memory
and no built-in support for input / output devices). It is also commonly
referred to as a CPU. 5
Software The programs or other operating information used by a computer and
storage media such as video cassettes audio tapes etc. requiring playback
on electronic equipment. 5
System-on-a-Chip (SoC) A user-designed fully-functional system implemented
on a single chip. This may include processing memory input / output
devices and other digital logic. 7
System-on-a-Programmable-Chip (SoPC) A System-on-a-Programmable Chip is
an SoC that is implemented using a high-density reconfigurable programmable
logic device (PLD). 7
references
[1] Katherine Barber. The Canadian Oxford Dictionary. Oxford University Press,
2005.