Embedded Systems Hardware

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Embedded Systems

Hardware and Software IssuesDept of Electronics and Telecommunication Engineering

Jadavpur University, Kolkata 700 032

and

International Institute of Information Technology

Kolkata 700 091


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Introduction

D. Mukhopadhyay

What are embedded systems?

How are embedded systems designed?

(Hardware and Software)

Critical Design challenges

Tools of the trade

Future directions


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What is an Embedded System?

Embedded systems are more limited inhardware and/or software functionality than a

personal computer.

An embedded system is designed to perform

a dedicated function. An embedded system is a computer system

with higher quality and reliability

requirements than other types of computer

systems.


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Embedded System?

Computational

but not first-and-foremost a computer

Integral with physical processes

sensors, actuators

Reactive

at the speed of the environment

Heterogeneous

hardware/software, mixed architectures

Networked

shared, adaptive


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Embedded Systems and their Markets

Market Embedded Device

Automotive Ignition System, Engine Control, Brake System

Consumer

Electronics

Digital and Analog Televisions, Set-Top Boxes,

Kitchen Appliances, Toys/Games, Telephones/Cell

Phones/Pagers, Cameras, GPS

Industrial

Controls

Robotics and Manufacturing Controls

Medical Infusion Pumps, Dialysis Machines, Prosthetic

Devices, Cardiac MonitorsNetworking Routers, Hubs, Gateways

Office

Automation

Fax Machine, Photocopier, Printers, Monitors,

Scanners


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Design of Embedded Systems

Task partitioning between hardware and

software

Hardware design and integration

Software development

System integration

Test strategies


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Hardware-Software Partitioning

Some tasks could be performed usinghardware or software.

Example:

A system receiving data packets needs tocalculate a Cyclic Redundancy Check (CRC)value. If the packet is OK, an ACK signalshould be sent within a specified time.

CRC could be calculated in S/W or bydedicated H/W.


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Criteria for choice between

H/W and S/W

Hardware adds a per unit cost

Software adds a fixed cost

Hardware provides speed Software provides flexibility

Software solution can reduce cost at

least when production is in highvolume

Hardware solution used when fastresponse is required


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Example of CRC check

Choice depends on how much time we have forsending the ACK signal

If S/W is too slow, we have no choice H/Wmust be used

If S/W can meet the timing spec., we coulduse S/W

S/W solution needs Real Time guarantee


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Hardware Design

Since a micro-controller in anembedded system will run just oneprogram all the time, hardwareresources must be matched to needs of

the application.

Modern technology has made it

possible to put the entire electronicsinclusive of sensors, analog circuits,digital circuits etc. on a single chip.(System On a Chip or SoC).


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Hardware Design Challenges

Compatibility of the entire system Interface design (linear to digital,

asynchronous to synchronous etc.)

Low power design

Modularity and ability to upgrade the system

in the field.

Time to market


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Low Power Design

Especially important in 3 cases1. Battery operated and mobile systemse.g.

a portable MP3 music player

2. Systems with a limited power sourcesuchas a smart public call booth which derives

power from phone lines.

3. High complexity and speed systemswhere heat dissipation is a problem


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Low Power Design Techniques

Power smart blocks which go to a lowpower or off mode when not in use.

Reduced voltage swing on loaded

buses Coding schemes which minimize the

number of transitions on signal lines

Reduced activity (toggling) Reduced capacitances

Superior device engineering


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Software Design

Software must provide the algorithms etc.needed for implementing the applications.

These algorithms often have an impact on

the choice of hardware as well.

For example, whether a DSP processor

should be used or not.

Most embedded system software needs to

be real time software.


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Generic Requirements

Software must be Modular

Each module should have local effects

Should be reusable, adaptable

Self documenting

In embedded systems, hardware and

software design must go hand in hand


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Real Time Systems

Real time systems have to guarantee that

they will respond to an external event withina specified amount of time.

Real Time systems dont have to be real

fast. They do have to be reliably on time.


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Type of Real Time Systems

Based on the type of timing guarantee

they provide, real time systems are

classified as

soft real time

or

hard real time.


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Soft Real Time Systems

Soft real time systems provide a time

guarantee, but missing an event is not

catastrophic.

For example, image decoding used duringsatellite TV reception must be completed

within a frame time.

If this guarantee is missed, there will be a

visible glitch.

Annoying but not catastrophic!


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Hard Real Time Systems

Hard real time systems are used when

missing a timing deadline will lead to

catastrophic results.

For example, a missile guidance system

should not miss any events!


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So why use soft real time

systems at all?

Both soft and hard real time systems

provide a real time guarantee. But if we can

afford to miss a few events, this guaranteed

response time can be much shorter.

Soft real time systems would be used in

non-critical applications which need to be

very fast.


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Hard and Soft

Real Time Systems

The time guarantee provided by soft real time

systems is statistical in nature whereas

that provided by hard real time systems is

absolute.

Design of soft real time systems optimizes

average case response whereas hard real

time systems must be designed for worstcase situations.


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Is real time software any different?

Interrupt handling has to be specially

careful.

Since interrupt handling and task

scheduling is done at the operating system

level, special real time compliant operating

systems should be used.


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Software Components

Device drivers

Schedulers

Real time routines

Non real time routines

Inter process communications

Pipes

Semaphores etc

Watchdog timers


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Inter-Process Communications

Signals

Pipes and FIFOs

Message Queues Semaphores

Shared Memory


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Future Directions Many more embedded systems will be full

systems on a single chip. This implies that

the software and hardware designs will

merge.

As systems on chip become more complex,software distributed over multiple

processors and running over different

memory spaces will become common


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Future Directions. Embedded systems will be developed in

unusual applications. For example: stress

detectors built into walls, powered and

accessed by RF beams.

Existing applications will become far moresophisticated with standardized user

interfaces such as web interfaces with

XML.


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Future Directions for

Developers

More and more multi-disciplinary expertise

will be required. For example biology-

chemistry-electronics and VLSI for bio-

sensors.

Fields of micro-processors, VLSI,

communications and information

technology will merge for developing

embedded systems.


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Discussion

What are the most challenging aspects of

these applications (and how does a

company make money) ?

Interaction mechanisms: sensors,

actuators, wireless networks Reliability and survivability

Infrastructure

Services Legislation

* * * * *


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Wireless Embedded System Networks


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Embedded System: A Connected Effort

Key Challenges

Control environmental parameters:

Temp, Humidity etc.Minimize power consumption

Cheap and small

Limited operation range of network:

Maximum 50 to 100 m

Low data rate per node: 1 10 bits/node(average)

Low mobility (at least 90% of nodes stationary)


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We Need Foundational Research

The science of computation has systematically

abstracted away the physical world. The scienceof physical systems has systematically ignored

computational limitations.

Embedded software systems, however, engage

the physical world in a computational manner.

It is time to construct a Hybrid Systems Science that

is simultaneously computational and physical.

Time, concurrency, robustness, continuums, and

resource management must be remarried to

computation.


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In Hardware

Low Power

Higher speed

Smaller size

Increased functionality

Increased productivity Reproducibility (especially in sensors and

actuators)

Networking and networked embedded systems


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But More So In Software

To create a modern computational systems science

and systems design practice with

Concurrency

Composability

Time

Hierarchy

Heterogeneity

Resource constraints

Portability Verifiability

Understandability

Documents

Embedded Systems Hardware