Transcript Embedded System

Design of Embedded Systems
UNIT I
EMBEDDED DESIGN LIFE CYCLE
Product specification – Hardware / Software partitioning – Detailed
hardware and software design – Integration – Product testing – Selection
Processes – Microprocessor Vs Micro Controller – Performance tools –
Bench marking – RTOS Micro Controller – Performance tools – Bench
marking – RTOS availability – Tool chain availability – Other issues in
selection processes.
A “short” list of Embedded Systems
Auto focus cameras
 ATMs
 Avionic systems
 Automatic transmission
 Battery Chargers
 Camcorders
 Cell phones
 Cordless Phones
 Digital Cameras
 DVD players
 Electronic Toys/Games
 Fax machines
 Medical Equipment
 Microwave ovens
 Modems
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Network cards
 Pagers
 PDAs
 Photocopiers
 Portable Video games
 Pont of Sales terminals
 Printers
 Scanners
 Satellite phones
 Teleconferencing
systems
 Televisions
 Set-top boxes
 VCR’s
 Video phones
and many more ….  Washers and dryers
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Embedded systems from real life
Mobile Phones and Base Stations
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Multiprocessor
 8-bit/32-bit for UI; DSP for signals
 32-bit in IR port; 32-bit in Bluetooth
8-100 MB of memory
All custom chips
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Massive signal processing
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Several processing tasks per connected
call
Based on DSPs
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Standard or custom
100s of processors
Embedded systems from real life
Sewing Machine
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User interface
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”Smart”
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Embroidery patterns
Touch-screen control
Sets pressure of foot depending
on task
Raise foot when stopped
New functions added by
upgrading the software
Embedded systems from real life
Cars
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Multiple
processors
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Up to 100
Networked
together
Large diversity in processor
types:
 8-bit – door locks, lights, etc.
 16-bit – most functions
 32-bit – engine control,
airbags
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Multiple networks
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Body, engine,
telematics, media,
safety
Functions by embedded
processing:
 ABS: Anti-lock braking
systems
 ESP: Electronic stability
control
 Airbags
 Efficient automatic
gearboxes
 Theft prevention with smart
keys
 Blind-angle alert systems
Embedded systems from real life
Smart Beer Glass
Capacitive
sensor for fluid
level
8-bit, 8-pin
PIC processor
Contact less
transmission
of power and
readings
Inductive coil for
RF ID activation &
power
CPU and reading coil in the
table. Reports the level of
fluid in the glass, alerts
servers when close to empty
Embedded systems from real life
Extremely Large
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Functions requiring
computers:
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Radar
Weapons
Damage control
Navigation
basically everything
Computers:
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Large servers
1000s of processors
Embedded systems from real life
Inside Your PC
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Custom processors
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32-bit processors
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Graphics, sound
IR, Bluetooth
Network, WLAN
Harddisk
RAID controllers
8-bit processors
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USB
Keyboard, mouse
Characteristics of Embedded Systems (1)
 Must be dependable,
• Reliability R(t) = probability of system working correctly
provided that is was working at t=0
• Maintainability M(d) = probability of system working
correctly d time units after error occurred.
• Availability A(t): probability of system working at time t
• Safety: no harm to be caused
• Security: confidential and authentic communication
Even perfectly designed systems can fail if the assumptions
about the workload and possible errors turn out to be wrong.
Making the system dependable must not be an after-thought,
it must be considered from the very beginning
Characteristics of Embedded Systems (2)
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Must be efficient
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Energy efficient
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Code-size efficient
(especially for systems on a chip)
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Run-time efficient
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Weight efficient
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Cost efficient
Dedicated towards a certain application
Knowledge about behavior at design time can be used
to minimize resources and to maximize robustness
Dedicated user interface
(no mouse, keyboard and screen)
Hybrid systems (analog + digital parts).
Characteristics of Embedded Systems (3)
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Many ES must meet real-time constraints
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A real-time system must react to stimuli from the
controlled object (or the operator) within the time interval
dictated by the environment.
For real-time systems, right answers arriving too late are
wrong.
„A real-time constraint is called hard, if not meeting
that constraint could result in a catastrophe“
[Kopetz, 1997].
All other time-constraints are called soft.
A guaranteed system response has to be explained
without statistical arguments
Frequently connected to physical environment
through sensors and actuators,
Characteristics of Embedded Systems (4)
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Typically, ES are reactive systems:
„A reactive system is one which is in continual
interaction with is environment and executes at a
pace determined by that environment“ [Bergé, 1995]
Behavior depends on input and current state.
 automata model appropriate,
model of computable functions inappropriate.
Not
every ES has all of the above characteristics.
Def.:
Information processing systems having most
of the above characteristics are called embedded
systems.
Why Embedded Systems Are
Different?
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Embedded systems are dedicated to specific
tasks, whereas PCs are generic computing
platforms.
Embedded systems are supported by a wide
array of processors and processor architectures.
Embedded systems are usually cost sensitive.
Embedded systems have real-time constraints.
Why Embedded Systems Are
Different?
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If an embedded system is using an operating
system at all, it is most likely using a real-time
operating system (RTOS), rather than
Windows 9X, Windows NT, Windows 2000,
Unix, Solaris, or HP- UX.
The implications of software failure are much
more severe in embedded systems than in
desktop systems.
Embedded systems often have power
constraints.
Embedded systems often must operate under
extreme environmental conditions.
Why Embedded Systems Are
Different?
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Embedded systems have far fewer system
resources than desktop systems.
Embedded systems often store all their
object code in ROM.
Embedded systems require specialized
tools and methods to be efficiently
designed.
Embedded microprocessors often have
dedicated debugging circuitry.
An embedded system example -- a
digital camera
Digital camera chip
CCD
CCD preprocessor
Pixel coprocessor
D2A
A2D
lens
JPEG codec
Microcontroller
Multiplier/Accum
DMA controller
Memory controller
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Display ctrl
ISA bus interface
UART
LCD ctrl
Single-functioned -- always a digital camera
Tightly-constrained -- Low cost, low power, small, fast
Reactive and real-time -- only to a small extent
Embedded System – A simplified view
CPU
embedded
computer
output
analog
input
analog
mem
Computer (programmable part) is surrounded by other
sub-systems, sensors and actuators.
The computer is called the micro-controller.
Its main functions are to monitor the physical
parameters of the surrounding systems and to control
these processes whenever needed. In some cases the
CPU is a DSP.
Typical Embedded System
Source : Embedded System Design Issues, Philip J. Koopman, ICCD96
Source : Embedded Systems Design,
Arnold S. Berger
HW / SW Design
HW & SW Development /
Debug
Hardware Design
51%
Software Design
Phase 7 : Maintenance and Upgrade
37%
Cost to fix bugs
Phase 6 : Acceptance testing
and Design
Phase 4 : Detailed
Phase 5 : HW / SW Integration
System
Specification
Phase 3 : Iteration
Phase 2 : HW / SW Partitioning
Phase 1 : Product Specification
The Embedded Design Life Cycle
System
Test
12%
Product Release
Tool-based view of the development cycle
Product Specification
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A common factor for the successful products
was that the design team (senior
management, marketing, sales, quality
assurance, and Engineering) shared a
common vision of the product they were
designing
In-circuit emulators
Hardware/Software Partitioning
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Partitioning decision- to decide which portion of
the problem will be solved in hardware and which
in software
It is possible to implement that algorithm purely
in software (the CPU without the FPU example),
purely in hardware (the dedicated modem chip
example), or in some combination of the two (the
video card example).
Laser Printer Design Algorithm
Data enters the printer and must be transformed into a legible ensemble of carbon
dots fused to a piece of paper
Concurrently, the processor services the data port and converts the incoming
data stream into a stream of modulation and control signals to a laser tube,
rotating mirror, rotating drum, and assorted paper-management “stuff.”
Iteration and Implementation
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This phase represents the early design work
before the hardware and software teams build “the
wall” between them
The hardware designers might be using simulation
tools, such as architectural simulators, to model
the performance of the processor and memory
systems.
The software designers are probably running code
benchmarks on self-contained, single-board
computers that use the target micro processor.
Hardware/Software Integration
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Big Endian/Little Endian Problem
Debugging an embedded or real-time
system
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Run control — The ability to start, stop, peak,
and poke the processor and memory.
Memory substitution — Replacing ROMbased memory with RAM for rapid and easy
code download, debug, and repair cycles.
Real-time analysis — Following code flow in
real time with real-time trace analysis.
Product Testing and Release
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Testing is more than making sure the
software doesn’t crash at a critical moment
Maintaining and Upgrading Existing
Products
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The majority of embedded system designers
(around 60 percent) maintain and upgrade
existing products, rather than design new
products.
The Selection Process
The Selection Process
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Is it available in a suitable implementation?
Is it capable of sufficient performance?
Is it supported by a suitable operating
system?
Is it supported by appropriate and adequate
tools?
Packaging the Silicon
Microprocessor versus Microcontroller
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Most embedded systems use microcontrollers instead of microprocessors
Microprocessor versus Microcontroller
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In a microprocessor-based system, the CPU and the various I/O
functions are packaged as separate ICs
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In a microcontroller-based system many, if not all, of the I/O
functions are integrated into the same package with the CPU
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The advantages of the microcontroller’s higher level of integration
are easy to see:
 Lower cost — One part replaces many parts.
 More reliable — Fewer packages, fewer interconnects.
 Better performance — System components are optimized for
their environment.
 Faster — Signals can stay on the chip.
 Lower RF signature — Fast signals don’t radiate from a large
PC board
Adequate Performance
Performance-Measuring Tools
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The Dhrystone benchmark is a simple C program that compiles to
about 2,000 lines of assembly code and is independent of operating
system services
Meaningful Benchmarking
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Real benchmarking involves carefully
balancing system requirements and variables
it’s important to analyze the real-time
behavior of the processor
Real-time performance can be generally
categorized into two buckets: interrupt
handling and task switching.
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EEMBC
The EEMBC benchmark consists of industry-specific tests
EEMBC
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EEMBC technical committee represent realworld algorithms against which the processor
can be measured
produces statistics on the number of times per
second the algorithm executes and the size of
the compiled code
RTOS Availability
RTOS Availability
Tool Chain Availability
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When evaluating the tool chain, integrated
coverage of these three broad categories:
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Compiler tools
Hardware and software debugging tools
Performance measuring tools
Compilers
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In-line assembly
Interrupt function
Assembly language list file generation
Standard libraries
Startup code
RTOS support
Tools integration
Optimizations
Support for Embedded C++ (EC++)
Hardware and Software Debugging
Tools
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An ICE
An interface to on-chip hardware debugging
resources
A ROM emulator
A logic analyzer
A performance analyzer
Other Issues in the Selection Process
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A prior commitment to a processor family
A prior restriction on language
Time-to-market factors
Summary
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Definition of Embedded Systems
Real Life Examples
ES Product Life Cycle in Design
Hardware / Software partitioning
Product testing
Selection Processes – Microprocessor Vs Micro
Controller
Performance tools – Bench marking
RTOS Micro Controller
Other issues in selection processes.