Chapter - One.ppt

Real-Time Embedded Systems
Abdi Mosisa
Chapter One
Introduction

Lecture: Introduction to
Embedded Systems
Embedded Real-Time Systems

Motivation
 Continuously increasing interest (in industrial, research and
education sectors) as well as rapid evolution in embedded
systems in the last years…
 Driving Forces:
 Progress in microelectronics / microprocessor technology, and
real-time operating systems (cost, performance, spread).
 Computer science / engineering is now part of the basic
education in all scientific fields, as well as part of everyday
life.
 Strong Belief: if a system can be controlled, it can be
controlled by a microprocessor!
 Huge industrial activity in embedded systems

What is an embedded system?
1. Special Purpose Computer System
2. Embedded or ‘hidden’ in another system
3. Has several restrictions in design / development / operation
4. Embedded systems are Reactive
5. Often, it may have real-time restrictions (requirements for
responding before a deadline expires)

What is an Embedded System?
 First, it is a computer system: anything that uses a
microprocessor, but is not a general-purpose computer:
 Consumer electronics:
 cellular phones, settop boxes, televisions, remote controls, game
consoles, Internet appliances, PDAs, Alarm Systems, hi-fi systems,
home cinemas,…
 Home appliances (“White Appliances”) like refrigerators, washing
machines (…which now-days include microprocessors and may also
have internet connection…)
 Telecommunications systems equipment
 Defense and weapon systems
 Automotive systems
 Systems for Process control
 Robots, Cars, Planes, Nuclear plants,…, include several
microprocessors / embedded systems
4

What is an Embedded System?
 Second, it is embedded, or ‘hidden’ inside another system:
 the user interacts with a special-purpose system, and not with
the computer inside the system
 the end-user typically does not or cannot modify or upgrade
the internal system himself

 Third, it has many sets of constraints / limitations, from the following:
 Cost (€0.1 adds up over thousand/million units…)
 Processor speed (for cost, size reasons)
 Memory (probably no hard disk, sometimes only few Kbytes only)
 Display and user interface (…also it may target users that are computer
illiterate)
 Network bandwidth (if network connection at all)
 Low Power Consumption (limited battery, lack of cooling system)
 Small Size, Low Weight (handheld devices, transportation cost issues)
 Reliability
 Safety-critical (must function correctly, must not function incorrectly)
 Security
 Operation in Harsh environmental conditions (Heat, vibration, shock,
power fluctuations, RF interference, lightning,…)

 Fourth: Embedded Systems are Reactive:
 computations occur in response to external events, that may
be:
 Periodic events (e.g., rotating machinery and control loops, timers,…)
 Aperiodic events (e.g., button closures, user interactions)
 Fifth: it may have real-time requirements (responding before a
deadline expires)
 Real-Time: timing correctness is part of system
correctness
 Hard real-time
 Absolute deadline, beyond which answer is useless
 Deadline may include minimum time as well as maximum time
 Soft real-time
 Occasionally missing a deadline is not catastrophic
 Utility of answer degrades with time difference from deadline
 In general, Real Time does not mean Real Fast

A Typical Embedded System
CPU
Cache
Memory
I/O
MMI
D/A
A/D
Microcontroller
Sensors Actuator
Auxiliary Systems
(power, cooling)
Diagnostic
tools
External
Environment
Electro-mechanical
backup and safety
And a customer’s
view…:
Reduced Cost
Increased Functionality
Improved Performance
Increased Dependability
An Embedded Designer's View…
CPU: Performance, Compilers, Operating Systems, Cost.
Memory Size, I/O connections, peripherals, Cost.
Functionality, Timetomarket, Cost & Cost.

Embedded System Examples – Diverse Restrictions
 Pocket remote control RF transmitter
 Software handcrafted for small size (less than 1 KB)
 Industrial equipment controller (e.g., elevator)
 Safetycritical software; realtime control loops
 Digital TV Set Top Box
 Software may be handcrafted at low layers, but at upper layers it supports
hardware agnostic applications downloadable over the network!
 Military signal processing (e.g., Radar/Sonar)
 Software handcrafted for extremely high performance

Trends in Embedded Systems
 Increasing code size
 migration from hand (assembly) coding to high-level
languages
 Reuse of hardware and software components
 processors (micro-controllers, DSPs)
 software components (drivers)
 Increasing integration and system complexity
 integration of RF, DSP, network interfaces,…
 32-bit processors, I/O processors

Microprocessor
 There exists at least one microprocessor in (the heart of) an
embedded system
 Microprocessor: CPU, memory, cache
 Microcontroller:
 Microprocessor, plus:
 Controllers for I/Os, peripherals, A/D-D/As, DMAs,
special devices tailored for specific application, etc.
 Extra Memory / Caches
 Microprocessors are general purpose - target a broad application
area
 Microcontrollers are specialized, tailored for specific applications
(e.g. for DVDs the microcontroller includes MPEG-2 hardware).

Embedded Systems:
Professional Opportunities

Why embedded systems are important?
 Embedded Systems dominate the worldwide computer system
market
 Yearly:
 The worldwide market of general purpose computers is of the
order of billion US $
 The worldwide market of embedded systems is also of the
order of billion US $
 ~100 million desktop PCs are produced
 ~7 billion microprocessors for embedded systems are
produced (one for each person on earth)
 While Desktop PC market is saturating, embedded market is
growing
 Embedded systems account for 90-95% of all microprocessors
produced worldwide!

Embedded System Categories
 General Computing
 Applications similar to desktop computing, but in an embedded package
(lower cost, targeting also computer illiterates,…)
 Settop boxes, game consoles, internet appliances, automatic tellers,
wearable computers),…
 Control Systems
 Closedloop feedback control of realtime systems
 Vehicle engines, chemical process, industrial process, nuclear power, flight
control,…
 Signal Processing
 Computations involving large data streams (signals)
 Radar, Sonar, video compression, Digital TV / HDTV broadcast centers…
 Communication & Networking
 Switching and information transmission
 Telephone systems, Internet, satellite systems…

Examples
 Telecommunications
 Wireline Access Systems
(copper enhancement,
DSLAM)
 Wireless Access Systems
(microwave systems)
 Terminal Equipments
(ISDN modems, DSL
modems, IP phones,
payphones,…)
 Defense Systems
 Secure Communications
 Crypto-systems

Examples
 General Computing
 DiTV Set-top boxes, Home-
Gateways, Home Networking
 Interactive TV Applications /
Electronic Program Guides
(embedded software)
 Content Distribution Systems
 Fleet Management Systems
 Systems and terminal equipment
for lottery operations
 Information kiosks
 Smart Cards Applications
 Cash Registers
 Energy Meters

Several Types of Embedded System Functions
 Applicationspecific interfacing
 Buttons, bells, lights,...
 Highspeed I/O
 Signal processing
 Multimedia data compression
 Digital filtering
 Control Laws
 PID control
 Fuzzy logic
 Sequencing logic
 Finite state machines
 Switching modes between control laws
 Fault response
 Detection & reconfiguration
 Diagnosis
 ...

Embedded Systems Designer’s Knowledge
 Hardware and Software
 The ‘low level’: computer architecture, micro-processors / micro-controllers,
assembly language, A/D-D/A converters, integrated circuit (ASIC/FPGA)
design
 The ‘higher level’: programming languages C/C++, (Java ?), object-oriented
systems
 Operating systems:
 …mainly the “lower half” of the OS (which is connected to h/w):
interrupts, synchronization, process communication, scheduling,
concurrency
 …but also the “upper half” (which is connected to applications)
 Embedded systems often use simple operating system kernels or real-time
operating systems, with typically small footprints and support for real-time
scheduling
 Applications: networking, signal processing, control

Embedded Systems Designer’s Skills
 Global System View
 …the system is not just the microprocessor…
 …not just digital logic…
 HW/SW Boundaries
 …optimal and under constraints (cost, space, performance,…)
 Products
 …from specs to production…
 …performance vs. cost trade-offs…
 …cost, cost, cost…
 …analyzability, how can I be sure that the system functions correctly?…
 …not just design – full product life-cycle…
 Will / Ability for Teamwork
 Communication Skills
 …other field scientists / engineers…
 …marketing, production…
 …end-customer…

Embedded System Designer: Global View
Multi-Discipline
 Electronic Hardware
 Mechanical Hardware
 Software
 Control Algorithms
 Signal Processing
 Humans
 Society/Institutions
MultiPhase
 Requirements
 Design
 Manufacturing
 Deployment
 Logistics
 Retirement
MultiObjective
 Dependability
 Affordability
 Safety
 Security
 Scalability
 Timeliness

Education
 Difficulties
 Embedded systems cover a wide spectrum of computer
science and various engineering sectors.
 Embedded Systems Education requires a wide background for
the students.
 Intensive lab training is required.
 Target
 Courses must focus in the System / global view (not just
relevant subjects e.g. operating systems, microprocessors,
etc.)

Embedded System Design approaches
 Embedded problems typically solved using one of the following
three approaches
 Use a combination of custom designed hardware and possibly
some software on an embedded processor that is integrated
with the hardware
 Use custom software designed to run on an off-the-shelf
embedded processor (our focus)
 Use an application specific processor (a processor that has
been optimized to run the specific class of applications
efficiently) with custom software

Pre-Requisite Knowledge/Skills
 Basic, working knowledge of computer architecture
 Knowledge of (and experience with) C programming
 Fundamentals of data structures and algorithms
 Just knowing Java is not enough
 Need to know, understand and manipulate “pointers”
 Some experience with assembly-language programming
 Knowledge of instruction sets of any modern microprocessors
(x86, ARM, PowerPC, 680x0, MIPS) should be a helpful
starting point

Chapter - One.ppt

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