SENG 440 Slides Lesson 01

7/25/2019 SENG 440 Slides Lesson 01

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SENG 440 Embedded Systems. Copyright c 2015 Mihai SIMA Lesson 1: Introduction

Lesson 1: Introduction

Characteristics and design of embedded systems an introduction

Quality & performance metrics measurable features of an ES implementation

Processors for embedded systems

Custom embedded processor design Comparison between ARM, Nios (Altera), MicroBlaze (Xilinx), 8051, 68HC11

Emphasize on ARM Software optimization techniques

What is wrong with plain software

Prole driven compilation Efficient C programming

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Outline

Embedded system denition

Embedded systems common characteristics

Examples of embedded systems

The desktop computer (PC)

Embedded system design process

Formalisms for embedded system design

Design metrics

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Embedded system denition

Hard to dene . Nearly any computing system other than a desktop computer

A device that includes a programmable computer but is not itself a general-

purpose computer

U.S. Supreme Court Justice Potter Stewarts famous quote about obscenity:

I know it when I see it

is a useful, if incomplete, guideline about embedded system.

Despite the difficulty in strictly dening embedded system, an observer can

usually tell when a subject is an embedded system based on a number of common characteristics

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Michael Barrs Embedded Systems Glossary

An embedded system is a special-purpose computer system designed to performa dedicated function

Unlike a general-purpose computer, an embedded system performs one or a fewpre-dened tasks, usually with very specic requirements, and often includestask-specic hardware and mechanical parts not usually found in a general-purpose computer

Since the system is dedicated to specic tasks, design engineers can optimize it,reducing the size and cost of the product

Embedded systems are often mass-produced, beneting from economies of scale.

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Embedded systems common characteristics

Single-functioned : repetitive execution of a specic task

Reactive and real time : continuously interaction with an environment, at a

speed imposed by the environment Tightly constrained : very tight constraints on various design metrics

Programmable, but usually not user programmable

Usually low power , low size, and low weight

Low cost

An embedded system is not always a separate block - very often it is physicallybuilt-in to the device it is controlling

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Examples of embedded systems

Simple appliances, such as washers and dryers

An appliance for a computationally intensive task, such as laser printing

A hand-held device, such as a cellular phone

An industrial controller in a factory

Telecommunications devices, such as modems

A safety-critical controller, such as an anti-lock brake controller in a car

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The desktop computer (PC)

Provides medium performance for a large number of applications

PC is user programmable, thus the end user can adapt it to do virtually anything

Price is on the order of hundreds of dollars

Size and weight (much) larger than the ES counterpart

Power consumption is still signicant

Operating systems running on PC are typically not real-time

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The embedded world

The programmer is exposed to hardware itself

Floating-point operations are typically not supported in hardware

Floating-point constructs translate into whole routines Fixed-point operations are highly recommended

Data-level parallelism is typically supported in hardware

Single Instruction Multiple Data (SIMD) Instruction-level parallelism may also be supported

Pipelined processors

Specialized computing blocks (peripherals) are widely used

C language is the necessary evil

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Embedded system design process

Encompasses different levels of abstraction : requirements, specication,structure, components, and system integration formalism is needed

We seek for an implementation that fullls desired functionality design metrics We have to nd good and cheap solutions (not necessarily the best and the

cheapest) in short time (not necessarily the shortest time)

We have to look at the embedded systems from an engineering point of view :adapt existing projects, use previous experience, and do not reinvent the wheel

We have to be able to speak a multitude of languages in order to describeefficiently the complex ordering and causality relations between the inputs andthe corresponding outputs

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Formalisms for embedded system design Why do we need a formalism for (embedded) system design?

Different design tasks at different level of abstraction Usually is a complex task carried out by a heterogenous team

The members of the team should speak the same (formal) language Unied Modeling Language (UML) (object-oriented)

The design is described as a number of interacting objects, rather than a fewlarge monolithic blocks of code

At least some of those objects will correspond to real pieces of hardware orsoftware in the system

Since UML is a language, it can be used for other design tasks as well, e.g.,writing large software package

Using UML rather than presenting UML is of interest for the course Youhave to read by yourselves: G. Booch, J. Rumbaugh, and I. Jacobson, The Unied Modeling Language User Guide , Addison-Wesley, 1999

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Design metrics

Design metric = a measurable feature of a systems implementation

Common design metrics:

NRE cost Unit cost Size Performance Power consumption Flexibility

Time-to-prototype Time-to-market Maintainability Correctness Safety ...

More details in F. Vahid and T. Givargis, Embedded System Design: A Unied Hardware/Software Introduction , John Wiley & Sons 2001

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Design metrics (contd) Non-Recurring Engineering (NRE) cost

One-time monetary cost of designing the system Once the system is designed, any number of units can be manufactured

without incurring any additional design cost

Example: NRE cost for printing a book includes the typesetting cost Time-to-market

The time required to develop a system to the point that it can be released and sold to customers

D

W W

Revenue

Delay = DMarket window = 2W

M a r k e

t r i s e

End of productlineopportunity

marketBeginning of

Percent Revenue Loss = D (3 W D )

2W 2 100

Example:W = 6 months and D = 2 monthPercent Revenue Loss = 45%

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Design metrics (contd)

Performance and Flexibility

Assume a computing engine that cannot meet the performance requirements Augment it with specialized computing units (e.g., MAC unit) Specialized computing unit(s) means lower exibility Balance between performance and exibility = fundamental trade-off in the

design of a computing engine

Power consumption

Specialized computing unit(s) means lower number of instructions Lower number of instructions means use power for computation instead of

instruction issuing

Unit cost Specialized computing units need additional silicon area

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Design metrics (contd)

There are so many design metrics

The design task is actually an optimization problem in a multi-dimensional space

Finding the optimum is a hot research/development area today

Given a problem (requirements and design tools), nd the optimum solution Given a problem build the design tools

Can the optimum solution be reached? For our course we will assume a linear cost function of design metrics:

Cost function = K 1

Performance +K 2

Flexibility +K 3

Power +...

Modeling the system can be a complex task

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Performance metric Performance = how long the system takes to execute a task

The most widely used design metric

Two main measures of performance: Latency : the time between the start of the tasks execution and the end Throughput : the number of tasks that can be processed per unit time

Speed-up : common method of comparing the performance of two systems:

speed-up of A over B = speed of Aspeed of B

To avoid confusion, say improve performance or improve execution time(latency) instead of increase performance and decrease execution time

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Firmware Terminology

Firmware = executable software that is stored within a ROM

The software written for embedded systems is often called rmware

Not entirely correct

The term rmware was originally used for micro-programs written for microsequencers.

Later on, rmware was coined to indicate a functional replacement for hardwareon low cost microprocessors.

Firmware can be thought of as semi-permanent since it remains the sameunless it is updated by a rmware updater.

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What we learned

Embedded systems are hard to dene

Designing an embedded system is an engineering task

Embedded systems design process includes different levels of abstraction

A formalism for embedded systems design is most welcome

Many design metrics put a high pressure on the design

U.S. Supreme Court Justice Potter Stewarts quote about obscenity

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About project Why ARM processor?

It is widely used in embedded systems There is a large amount of software

The ARM Company

It does not manufacture processor chips It licenses an instruction set, that is, an architecture

There are many vendors that provide ARM chips

For ARM I can provide:

Cross-compiler (runs on an Intel-Linux box, generates ARM-Linux executable) Simulator (runs on an Intel-Linux box)

Installing and using Linux is recommended for all students

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List of available projects My oppinion : the embedded systems market requires the following projects

Color Space Conversion (RGB-to-YCC and YCC-to-RGB)

Audio compression and decompression (A law, law) Discrete Cosine Transform and Inverse Discrete Cosine Transform Discrete Fourier Transform and Inverse Discrete Fourier Transform RSA Cryptography based on Montgomery Multiplication Matrix diagonalization and matrix inversion FIR and IIR ltering Hufmann encoding and decoding Motion estimation COordinate Rotation DIgital Computer (CORDIC)

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Project main goals Write C code that implements a specic task using strictly xed-point arithmetic

Fixed-point arithmetic requires a little bit of attention

Reduced dynamic range (example: with 8 bits we can represent at most 256different values, so that the entire world is shrinked to 256 values)

Innity cannot be mapped to a nite value, therefore it is the programmerresponsibility to determine the largest value to be represented within aparticular precision

Truncation and round-off errors should be of particular concern

Augment the ARM standard instruction set with a new instruction

Unfortunately, the compiler wont be able to detect the new instruction, andtherefore it is the programmer responsibility to explicitly instantiate the newoperation (for example, by means of assembly inlining constructs)

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