Real-time embedded components and systems : with Linux and RTOS

475 Pages·2016·8.78 MB·english

by  Pratt

R -T
EAL IME
E
MBEDDED
C
OMPONENTS
S
AND YSTEMS
with L and RTOS
INUX
Sam Siewert
John Pratt
MERCURY LEARNING AND INFORMATION
Dulles, Virginia
Boston, Massachusetts
New Delhi
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S. Siewert and J. Pratt. Real-Time Embedded Components and Systems with LINUX and RTOS.
ISBN: 978-1-942270-04-1
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PREFACE
This book is intended to provide the practicing engineer with the necessary
background to apply real-time theory to the design of embedded components
and systems in order to successfully field a real-time embedded system. The
book also is intended to provide a senior-year undergraduate or first-year grad-
uate student in electrical engineering, computer science, or related fields of
study with a balance of fundamental theory, review of industry practice, and
hands-on experience to prepare for a career in the real-time embedded system
industries. Typical industries include aerospace, medical diagnostic and thera-
peutic systems, telecommunications, automotive, robotics, industrial process
control, media systems, computer gaming, and electronic entertainment, as
well as multimedia applications for general-purpose computing. Real-time sys-
tems have traditionally been fielded as hard real-time applications, such as digi-
tal flight control systems, antilock braking systems, and missile guidance. More
recently, however, intense interest in soft real-time systems has arisen due to
the quickly growing market for real-time digital media services and systems.
This updated edition adds three new chapters focused on key technology ad-
vancements in embedded systems and with wider coverage of real-time archi-
tectures. The overall focus remains the RTOS (Real-Time Operating System),
but use of Linux for soft real-time, hybrid FPGA (Field Programmable Gate
Array) architectures and advancements in multi-core system-on-chip (SoC),
as well as software strategies for asymmetric and symmetric multiprocessing
(AMP and SMP) relevant to real-time embedded systems, has been added.
Specifically, a new Chapter 9 provides an overview of RTOS advancements,
including AMP and SMP configurations, with a discussion of future directions
for RTOS use in multi-core architectures, such as SoC. A new Chapter 10 is
devoted to open source RTOS, with emphasis on FreeRTOS. A new Chapter
11 is focused on methods to integrate embedded Linux into real-time embed-
ded systems, with emphasis on soft real-time requirements, methods to patch
and improve the Linux kernel for predictable response, and finally best prac-
tices for implementation of real-time services and applications that make use of
POSIX real-time extensions in the 1003.1 2013 standard. The original Chapters
9, 10, and 11 have been preserved and are now Chapters 12 to 14, and Part
III remains unchanged other than chapter renumbering to accommodate the
insertion of the new chapters.
xii (cid:129) PREFACE
John Pratt, a new co-author, has contributed extensively to this edition, with
specific focus on FreeRTOS, and brings a unique perspective to this updated
version with his commercial mobile embedded systems expertise.
The new Linux examples and extended coverage of Linux in this edition
are based upon a summer version of the course Real-Time Embedded Systems
taught at the University of Colorado, Boulder, to offer an alternative to the tra-
ditional fall course that has used the Wind River VxWorks RTOS. The summer
course has emphasized the same hard and soft real-time theory, but practice
has focused on using Linux to achieve predictable response for systems that
require real-time, but where occasional missed deadlines are not catastrophic.
For example, mobile digital media, augmented reality applications, computer
vision and digital entertainment and interactive systems. While hard real-time
mission critical systems are still a major concern, many emergent applications
require predictable response and simply need to provide high-quality of ser-
vice. The use of buffering and time stamps to work ahead and provide high-
quality presentation of results is, for example, a method used in digital video
encode, transport, and decode, where the systems software is not required to
provide deterministic proven hard real-time processing, as has been the goal
for the RTOS. Likewise, many systems today use best-effort or soft real-time
embedded Linux configurations with coprocessors, either FPGA or ASIC (Ap-
plication Specific Integrated Circuits), that provide guaranteed hard real-time
processing with hardware state machines.
Numerous improvements and corrections have been made to the original
edition text to improve readability and clarity based on excellent feedback by
many undergraduate and graduate students at the University of Colorado who
have used the original edition text since August 2006.
While it’s impossible to keep up with all the advancements related to real-
time embedded systems, we hope the reader will find the new chapters and
expanded example material included on the DVD a useful extension to tradi-
tional cyclic executive and RTOS real-time system components and systems
architecture. The expanded guidelines and strategies are intended to help the
practicing engineer and to introduce advanced undergraduate and graduate
students in computer and software engineering disciplines to design strategies
and methods to tackle many of the challenges found in real-time embedded
systems. This challenging engineering area continues to evolve and relies upon
the careful validation and verification efforts of practicing engineers to ensure
and balance safety, cost, and capabilities of these complex and critical applica-
tions on which we all depend.
PREFACE (cid:129) xiii
Companion Files
Companion files (figures and code listings) for this title are also available by
contacting [e-mail].
Sam Siewert
December 2015
CONTENTS
Preface xi
Acknowledgments xv
Part I: Real-Time Embedded Theory
Chapter 1 Introduction 3
1.1 Introduction 3
1.2 A Brief History of Real-Time Systems 4
1.3 A Brief History of Embedded Systems 7
1.4 Real-Time Services 7
1.5 Real-Time Standards 16
Summary 18
Exercises 18
Chapter References 19
Chapter 2 System Resources 21
2.1 Introduction 21
2.2 Resource Analysis 23
2.3 Real-Time Service Utility 31
2.4 Scheduling Classes 38
2.4.1 Multiprocessor Systems 39
2.5 The Cyclic Executive 39
2.6 Scheduler Concepts 41
2.6.1 Preemptive vs. Non-preemptive Schedulers 44
2.6.2 Preemptive Fixed-Priority Scheduling Policy 47
2.7 Real-Time Operating Systems 50
2.8 Thread-Safe Reentrant Functions 59
Summary 61
Exercises 62
Chapter References 64
Chapter 3 Processing 67
3.1 Introduction 67
3.2 Preemptive Fixed-Priority Policy 68
3.3 Feasibility 72
3.4 Rate-Monotonic Least Upper Bound 73
3.5 Necessary and Sufficient Feasibility 84
3.5.1 Scheduling Point Test 84
3.5.2 Completion Time Test 87
vi (cid:129) CONTENTS
3.6 Deadline-Monotonic Policy 89
3.7 Dynamic-Priority Policies 91
Summary 95
Exercises 96
Chapter References 98
Chapter 4 Resources 99
4.1 Introduction 99
4.2 Worst-Case Execution Time 100
4.3 Intermediate IO 104
4.4 Execution Efficiency 107
4.5 IO Architecture 110
Summary 111
Exercises 112
Chapter References 113
Chapter 5 Memory 115
5.1 Introduction 115
5.2 Physical Hierarchy 116
5.3 Capacity and Allocation 120
5.4 Shared Memory 120
5.5 ECC Memory 121
5.6 Flash File Systems 126
Summary 127
Exercises 128
Chapter References 128
C hapter 6 Multiresource Services 129
6.1 Introduction 129
6.2 Blocking 130
6.3 Deadlock and Livelock 130
6.4 Critical Sections to Protect Shared Resources 132
6.5 Priority Inversion 132
6.5.1 Unbounded Priority Inversion Solutions 134
6.6 Power Management and Processor Clock Modulation 138
Summary 139
Exercises 139
Chapter References 140
Chapter 7 Soft Real-Time Services 141
7.1 Introduction 141
7.2 Missed Deadlines 142
7.3 Quality of Service 143
7.4 Alternatives to Rate-Monotonic Policy 144
CONTENTS (cid:129) vii
7.5 Mixed Hard and Soft Real-Time Services 147
Summary 148
Exercises 148
Chapter References 149
Part II: Designing Real-Time Embedded Components
Chapter 8 Embedded System Components 153
8.1 Introduction 153
8.2 Hardware Components 155
8.2.1 Sensors 155
8.2.2 Actuators 158
8.2.3 IO Interfaces 159
8.2.4 Processor Complex or SoC 163
8.2.5 Processor and IO Interconnection 164
8.2.6 Bus Interconnection 165
8.2.7 High-Speed Serial Interconnection 170
8.2.8 Low-Speed Serial Interconnection 172
8.2.9 Interconnection Systems 173
8.2.10 Memory Subsystems 174
8.3 Firmware Components 176
8.3.1 Boot Code 176
8.3.2 Device Drivers 177
8.3.3 Operating System Services 178
8.4 RTOS System Software 178
8.4.1 Message Queues 179
8.4.2 Binary Semaphores 180
8.4.3 Mutex Semaphores 181
8.4.4 Software Virtual Timers 181
8.4.5 Software Signals 182
8.5 Software Application Components 182
8.5.1 Application Services 182
8.5.2 Reentrant Application Libraries 185
8.5.3 Communicating and Synchronized Services 186
Summary 188
Exercises 188
Chapter References 189
Chapter 9 Traditional Hard Real-Time Operating Systems 191
9.1 Introduction 191
9.2 Evolution of Real-Time Scheduling and Resource Management 192
9.3 AMP (Asymmetric Multi-core Processing) 194
9.4 SMP (Symmetric Multi-core Processing) 199
viii (cid:129) CONTENTS
9.5 Processor Core Affinity 200
9.6 Future Directions for RTOS 216
9.7 SMP Support Models 217
9.8 RTOS Hypervisors 218
Summary 219
Exercises 219
Chapter References 220
Chapter 10 Open Source Real-Time Operating Systems 221
10.1 FreeRTOS Alternative to Proprietary RTOS 221
10.2 FreeRTOS Platform and Tools 225
10.3 FreeRTOS Real-Time Service Programming Fundamentals 228
Exercises 235
Chapter References 235
Chapter 11 Integrating Embedded Linux into Real-Time Systems 237
11.1 Introduction 237
11.2 Embedding Mainline Linux: Interactive and Best-Effort 238
11.3 Linux as a Non-Real-Time Management and
User Interface Layer 244
11.4 Methods to Patch and Improve Linux for Predictable Response 245
11.5 Linux for Soft Real-Time Systems 249
11.6 Tools for Linux for Soft Real-Time Systems 249
Summary 250
Exercises 250
Chapter References 251
Chapter 12 Debugging Components 253
12.1 Introduction 253
12.2 Exceptions 254
12.3 Assert 262
12.4 Checking Return Codes 263
12.5 Single-Step Debugging 264
12.6 Kernel Scheduler Traces 273
12.7 Test Access Ports 278
12.8 Trace Ports 280
12.9 Power-On Self-Test and Diagnostics 282
12.10 External Test Equipment 287
12.11 Application-Level Debugging 291
Summary 292
Exercises 293
Chapter References 293