Table Of ContentEmbedded Realtime
Systems Programming
Embedded Realtime
Systems Programming
Sriram V Iyer
Pankaj Gupta
Philips Semiconductors Design
Competence Centre, Bangalore
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Address……………………………………….........................
MMccGGrraaww--HHiillll
The Companies
To my parents, Venkateswaran R & Lalitha V
my sister, Harini Deepak
–Sriram V Iyer
To my parents, PremChand & Omwati
my brothers Deepak & Vijay and my wife, Purnima
–Pankaj Gupta
And to the Philips ‘family’—as our CEO
Dr Bob Hoekstra rightly calls our organisation
PPrreeffaaccee
As we think of writing the preface, we are filled with thoughts on this book, which took over 20
months to reach this shape.
Embedded industry is now in its adolescent phase—Too young to be called mature and too
mature to be called nascent. It is currently experiencing the ‘growing pains’. The industry once
restricted to a very small community is beginning to embrace more and more architects and
developers into its fold.
When we started out in this industry after our college, a sense of mystery took over. We were
familiar with programming in the colleges. We did do a course on programming (typically
C/C++/Java), data structures/algorithms etc as a part of our curriculum. Programming in an
embedded-realtime scenario gave a feeling of deja vuof our previous programming experiences
though new experiences were definitely different.
As we patiently took notes, conversed wit senior colleagues and by sifting through a mam-
moth amount of information in the web, things started becoming clear. Finally, we could com-
prehend the rules that differentiate embedded programming from normal desktop/applications
programming. It by no way means we have reached nirvana of embedded-realtime program-
ming. We have just crossed the first few basic steps that we would like to share it with you.
This time, we were asked by Mr. K.M. Jayanth, the Department Manager of the department
we work for, to compile our thoughts, experiences and information we had gathered and create
a primer on embedded-realtime software for our department. We ventured into this activity
without knowing what we were stepping into. As we started we saw that the project was indeed
huge. After numerous sleepless nights, gallons of caffeine and countless pizzas we could finally
constrain ourselves to writing a 100 odd pages for that primer. We clearly felt that we were “hun-
gry” for a lot more but had to restrict the content to this level for it to remain a ‘primer’.
At the same time, we got a mail from Deepa (Manager, Professional Publishing, TMH) if a
book on C++ could be written on seeing some C++ articles* in ITspace.com. We decided that
a book on programming embedded-realtime systems would be more appropriate for us, than a
book on C++.
This book is our collective wisdom distilled over hours of design, development, integration
and debugging experiences. The contents were also developed with interaction with many of
*Sriram V Iyer was the community guide/moderator for the C++ section in ITspace.com
viii
Preface
our colleagues and intelligent conversations during the series of a seminar on embedded-real-
time systems that we conduct in our department.
AAuuddiieennccee
The audience of the book could range from a novice developer who is curious to know more
about embedded systems. It could be of immense use to a practicing embedded engineer to
know more about the covered topics. It could also be used as an undergraduate text for CS, EE
and courses in Embedded-Realtime systems.
The book is not intended to replace courses in microprocessors, algorithms, programming
but can definitely complement this courses.
Though this book talks a lot about software interactions with hardware, the focus of the book
is restricted only to software. Though some insights are provided in some chapters, this book
definitely does not address the issue of embedded hardware design.
OOrrggaanniissaattiioonn ooff tthhee BBooookk
The Section 1 “Introduction” is an introduction to the theory behind embedded-realtime systems.
It discusses the fundamental differences between programming in desktop and embedded sys-
tems. It describes various attributes of these systems along with some of their limitations that
make programming these systems interesting!
The Section 2 “Embedded nitty-gritty” delves into the details of embedded systems program-
ming. Chapter 2 describes the elements of the build process with emphasis on features unique
to embedded systems. Details of various steps like pre-processing, compiling, linking, locating
etc are covered in length. Chapter 3 describes various types of memories. The knowledge of
these types of memory and how they work is essential for any embedded engineer when design-
ing his system. Chapter 4 delves into various techniques to handle the memory that is so pre-
cious for any embedded system. Internal details of various memory allocation schemes are
described. It also lists some interesting bugs and their solutions. The Chapter 5 on Interrupts and
ISRs covers in great depth the concept of interrupts. Various types of interrupts, ISRs are cov-
ered. The chapter ends with general guidelines for writing efficient ISRs and some interesting
debugging tips.
Section 3 “Correctness is not enough” focuses on the ‘realtime’ aspect. Chapter 6 describes the
mathematics of scheduling theory and covers the famous Rate Monotonic Analysis (RMA). This
chapter should be interesting for engineers to know the basics of realtime theory and hopefully
inspire them to go further. The Chapter 7 on RTOS is no doubt one of the most famous topics
among the embedded community. The RTOS chapter describes various RTOS concepts like
tasks, queues, events, timers and race-conditions, priority inversion etc. It also has interesting
discussions on priority inversion & Mars Rover mission, history on nomenclature in sema-
phores, etc.
Section 4, aptly named “But I know this already!” discusses various Software Engineering
aspects of designing embedded-realtime systems. Many of the books on embedded-realtime
ix
Preface
theory do not include content on software engineering aspects of embedded system design
though many of the principles remain the same across various software domains. Chapter 8
describes in detail the “Requirements Engineering” principles that need to be followed to cre-
ate a system as intended by the customer/end-user. Following sound requirements engineering
concepts will help us avoid nasty surprises during the delivery of the system. Chapter 9
“Architecture and Design of Embedded Systems” covers the high-level software architecture and
design aspects of embedded systems. The topic of software architecture and design is huge and
many independent books are available to address the topic. The chapter focuses on some of the
issues including some “Architecture Patterns” that are relevant to embedded-realtime systems.
The Chapter 10 “Implementation Aspects in Embedded Systems” discusses a plethora of tech-
niques that can be applied in embedded systems ranging from bit-fields to endianness, callback
systems to state machines. Chapter 11 “Embedded Software Estimation Modelling” describes
some of the techniques in software estimation in embedded systems. Estimation, as its name
indicates is still considered more as an art and a result of experience rather than an engineering
discipline. This chapter helps in making estimation of software in embedded systems more accu-
rate. The Chapter 12 “Debugging and Validation of Embedded Systems” discusses one of the
most dreaded times of any embedded engineer—debugging. This chapter throws light on some
of the concepts on debugging and various tools available for the same.
The book ends with a detailed bibliography and an appendix on “C++ for Embedded/
Realtime Systems”, a paper presented by Sriram V Iyer and Manoj Kamath (Philips Semi-
conductors, Philips Software Centre) in Philips TechSym 2001, a technology symposium con-
ducted in Philips Innovation Campus.
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The authors would like to express their heart-felt gratitude to Philips for providing a congenial
and nurturing environment for our thoughts on the subject. We especially owe a lot to Jayanth,
Department Manager DSS for providing constant support and feedback during the entire dura-
tion of this big exercise. We also thank Dr Antonio, Director PS DCC-B, Philips for finding time
out of his busy schedule to review the manuscript and write the beautiful preface of the book.
The writers would like to say, “thanks buddies” to our teams in Philips who constantly pulled
our legs and created perfect atmosphere for this creative endeavor.☺
Sriram V Iyer
Pankaj Gupta
FFoorreewwoorrdd
In times when the pace of change was slow, the variety of products and services was small, the
channels of communication and distribution less explosive, and the consumer needs less sophis-
ticated, engineering could enjoy prolonged periods of relative stability. The times when the
customer can be held almost constant and the optimisation of other variables could have been
optimised are over. These times have long gone.
Now, human beings live in times of choice. They are continuously bombarded with pur-
chasing alternatives in every aspect of their lives. They demand more and more from their
purchases and their suppliers. The markets are fragmented and their products can be tailored by
design, programmability, service and variety. In the world of high technology such as
Semiconductors, there is an analogy that can explain this process: behind the proliferation of
electronic components, infiltrating our communication systems, entertainment centers, trans-
port, homes, there are thousands of integrated circuits that are produced in high volume up to
the last layer, which in turn is designed by the customer to add the final touch of personality
needed for their specific products. Radical customization dramatically has shortened time-to-
market and time-to-money. This exemplifies the remaking of our means of production to accom-
modate our ever-changing social and personal needs.
Programming embedded and realtime systems is not an exception to the rule—this also ben-
efits from the flexibility the topic has to offer. It emphasizes the best-practice approach but allows
the necessary customisation to shorten the time-to-market deliverables.
One of the functions of this book, and perhaps the most important one, is to open up the logic
of applying the appropriate fundamentals on embedded software and realtime systems, so that
everyone in the software industry can participate in the understanding of best practices. If pru-
dence rather than brilliance is to be our guiding principle, then many fundamentals are far bet-
ter than a series of sophisticated but isolated experiences. If embedded software is going to be
the semiconductors driving force, and most of the semiconductor organisations are debating and
insist this is their actual goal, then its fundamentals must be accessible to all players, and not as
is sometimes the case, be reserved to an elect few who think that software engineering is just a
part of the system approach.
Finally, I would like to make you think that this work is going to remain the basics of engi-
neering despite the fast-paced, ever changing competitive world. This book will continue mak-
ing you think about engineering basics and the way you think about engineering. But it will also
make you think about fundamentals of software engineering.
I am confident the reader will enjoy and find Embedded-Realtime Systems Programming a
useful experience.
Dr. Antonio M. Alvarez-Tinoco
Director, Philips Semiconductors
Design Competence Centre–Bangalore
Contents
Preface vii
Foreword xi
Section One: Introduction
CChhaapptteerr 11 IInnttrroodduuccttiioonn ttoo EEmmbbeeddddeedd RReeaallttiimmee SSyysstteemmss 3–18
1.1 Challenges for Embedded Systems 5
1.2 Fundamental components of Embedded Systems 7
1.3 Examples of Embedded Systems 12
1.4 Languages for Programming Embedded Systems 14
1.5 Organisation of the Book 14
1.6 Lessons Learnt 17
1.7 Review Questions 18
Section Two: Embedded nitty-gritty
CChhaapptteerr 22 TThhee BBuuiilldd PPrroocceessss ffoorr EEmmbbeeddddeedd SSyysstteemmss 21–48
2.1 Pre-Processing 22
2.2 Compiling 26
2.3 Cross Compiling 27
2.4 Linking 29
2.5 Locating 30
2.6 Compiler Driver 30
xiv
Contents
2.7 Linker MAP Files 31
2.8 Linker Scripts and Scatter Loading 34
2.9 Loading on the Target 35
2.10 Program Segments 36
2.11 Under the hood—Function Calling Mechanism 42
2.12 Lessons Learnt 47
2.13 Review Questions 48
CChhaapptteerr 33 TTyyppeess ooff mmeemmoorryy 51–67
3.1 Memory Access Procedure 52
3.2 Types of Memory 57
3.3 Lessons Learnt 66
3.4 Review Questions 67
CChhaapptteerr 44 MMeemmoorryy MMaannaaggeemmeenntt iinn EEmmbbeeddddeedd RReeaallttiimmee SSyysstteemmss 69–91
4.1 Memory management methods 69
4.2 General Treatise on Pointer-Related Bugs 89
4.3 Lessons Learnt 90
4.4 Review Questions 91
CChhaapptteerr 55 IInntteerrrruuppttss aanndd IISSRRss 93–127
5.1 What is an interrupt? 93
5.2 Polling Vs Interrupts 95
5.3 The Jargon Soup: Types of Interrupts 96
5.4 Interrupt Latency 98
5.5 Re-entrancy 98
5.6 Interrupt Priority and Programmable Interrupt Controllers 103
5.7 Types of ISRs 105
5.8 Looking under the hood on how interrupts work 113
5.9 Guidelines for Writing ISRs 117
5.10 Debugging ISRs 121
5.11 Lessons Learnt 126
5.12 Review Questions 127
