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Embedded Computing

Design & Co-design of

Embedded Systems

Maziar Goudarzi

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Today Program

Introduction to Embedded Systems

What are embedded systems?

Challenges in embedded computing

system design.

Design methodology.

Copyright Note:Main idea from Prof. Wolfs overheads for his book:

Computers as Components, MKP 2001.

Plus some modifications and additions.

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Introduction

What are embedded systems?

Challenges in embedded computing

system design.Design methodologies.

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Definition

Definition: Embedded System

Includes a programmable computer

But, is not a general-purpose computer

CPU

mem

input

output analog

analog

embedded

computer

Logic

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Embedded Systems

Advantages

Optimizations according to application

characteristicsdont need all the general-purpose

bells and whistles

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Examples

Embedded

System

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Early history

Late 1940s: MIT Whirlwind computer wasdesigned for real-time operations.

Originally designed to control an aircraftsimulator.

First microprocessor was Intel 4004 in

early 1970s.HP-35 calculator used several chips to

implement a microprocessor in 1972.

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Early history, contd.

Usage in automobiles ECU

Starting in 1970s.

Control fuel/air mixture, engine timing, etc.Multiple modes of operation: warm-up,

cruise, hill climbing, etc.

Provides lower emissions, better fuelefficiency.

Native example: Cadillac Iran!

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Microprocessor varieties

Microcontroller:includes I/O devices, on-board memory.

Digital signal processor (DSP):microprocessor optimized for digital signalprocessing.

Typical embedded word sizes: 8-bit, 16-bit, 32-bit.

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Application examples

Simple control: front panel of microwaveoven, etc.

Canon EOS 3 has three microprocessors.32-bit RISC CPU runs autofocus and eye

control systems.

Analog TV: channel selection, etc.Digital TV: programmable CPUs +

hardwired logic.

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Automotive embedded

systems

Todays high-end automobile may have 100microprocessors:

4-bit uController checks seat belt;

uControllers run dashboard devices;

16/32-bit uP controls engine.

Native examples

Samand LXPeugeot Persia ELX

Xantia, ...

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BMW 850i, contd.

brake

sensor

brake

sensor

brake

sensor

brake

sensor

ABShydraulic

pump

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Characteristics of

embedded systems

Sophisticated functionality.

Real-time operation.

Low manufacturing cost.

Low power.

Designed to tight deadlines by smallteams.

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Non-functional

requirements

Many embedded systems are mass-market items that must have low

manufacturing costs.Limited memory, microprocessor power, etc.

Power consumption is critical in battery-

powered devices.Excessive power consumption increases

system cost even in wall-powered devices.

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Design teams

Often designed by a small team ofdesigners.

Often must meet tight deadlines.6 month market window is common.

Cant miss back-to-school window for

calculator.

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Why use microprocessors?

Alternatives:

field-programmable gate arrays (FPGAs),

custom logic, etc.Microprocessors are often very efficient:

can use same logic to perform many

different functions.Microprocessors simplify the design of

families of products.

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The performance paradox

Microprocessors use much more logic toimplement a function than does custom

logic.But microprocessors are often at least as

fast:

heavily pipelined;large design teams;

aggressive VLSI technology.

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Power

Custom logic is a clear winner for lowpower devices.

Modern microprocessors offer features tohelp control power consumption.

Software design techniques can help

reduce power consumption.Transmetas Crusoe Processor (one of the

optional reading-assignments)

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Embedded Computing

Challenges in Embedded

System Design

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Challenges in embedded

system design

How much hardware do we need?

How big is the CPU? Memory?

How do we meet our deadlines?Faster hardware or cleverer software?

How do we minimize power?

Turn off unnecessary logic? Reduce memoryaccesses?

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Challenges, etc.

Does it really work?

Is the specification correct?

Does the implementation meet the spec?How do we test for real-time characteristics?

How do we test on real data?

How do we work on the system?Observability, controllability?

What is our development platform?

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Embedded Computing

Design Methodology

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Design methodologies

A procedure for designing a system.

Understanding your methodology helps

you ensure you didnt skip anything.Compilers, software engineering tools,

computer-aided design (CAD) tools, etc.,

can be used to:help automate methodology steps;

keep track of the methodology itself.

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Design goals

Functionality and user interface.

Performance.

Overall speed, deadlines.

Manufacturing cost.

Power consumption.

Other requirements (physical size, etc.)

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Levels of abstraction

requirements

specification

architecture

component

design

system

integration

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Stepwise refinement

At each level of abstraction, we must:

analyzethe design to determine

characteristics of the current state of thedesign;

refinethe design to add detail.

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Requirements

Plain language description of what theuser wants and expects to get.

May be developed in several ways:talking directly to customers;

talking to marketing representatives;

providing prototypes to users for comment.

F ti l

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Functional vs. non-

functional requirements

Functional requirements:

output as a function of input.

Non-functional requirements:time required to compute output;

size, weight, etc.;

power consumption;reliability;

etc.

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Our requirements form

name

purpose

inputs

outputsfunctions

performance

manufacturing cost

powerphysical size/weight

E l GPS i

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Example: GPS moving map

requirements

Moving mapobtains position

from GPS, paintsmap from localdatabase.

lat: 40 13 lon: 32 19

I-78

ScotchRoad

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GPS moving map needs

Functionality: For automotive use. Showmajor roads and landmarks.

User interface: At least 400 x 600 pixelscreen. Three buttons max. Pop-up menu.

Performance: Map should scroll smoothly.

No more than 1 sec power-up. Lock ontoGPS within 15 seconds.

Cost: $500 street price = approx. $100

cost of goods sold.

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GPS i

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GPS moving map

requirements form

name GPS moving map

purpose consumer-grademoving map for driving

inputs power button, twocontrol buttons

outputs back-lit LCD 400 X 600functions 5-receiver GPS; three

resolutions; displayscurrent lat/lon

performance updates screen within0.25 sec of movement

manufacturing cost $100 cost-of-goods-soldpower 100 mW

physical size/weight no more than 2: X 6:,12 oz.

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Specification

A more precise description of the system:

should not imply a particular architecture;

provides input to the architecture designprocess.

May include functional and non-functional

elements.May be executable or may be in

mathematical form for proofs.

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GPS specification

Should include:

What is received from GPS;

map data;user interface;

operations required to satisfy user requests;

background operations needed to keep thesystem running.

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Architecture design

What major components go satisfying thespecification?

Hardware components:CPUs, peripherals, etc.

Software components:

major programs and their operations.

Must take into account functional andnon-functional specifications.

GPS moving map block

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GPS moving map block

diagram

GPS

receiver

search

engine renderer

user

interfacedatabase

display

GPS moving map hardware

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GPS moving map hardware

architecture

GPS

receiver

CPU

panel I/O

display frame

buffer

memory

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Designing hardware and

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Designing hardware and

software components

Must spend time architecting the systembefore you start coding.

Architecture componentsSome are ready-made,

Some can be modified from existing designs

Others must be designed from scratch.

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System integration

Put together the components.

Many bugs appear only at this stage.

Have a plan for integrating components touncover bugs quickly, test as muchfunctionality as early as possible.

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Other Notes

Course web-page is now establishedhttp://ce.sharif.edu/courses/84-85/1/ce226/index.php