Computers as Components Principles of Embedded Computing System Design Dr. Prof. Huang Tingle Group...

Computers as ComponentsPrinciples of EmbeddedComputing System Design

Dr. Prof. Huang Tingle

Group of IIPIGuilin University of Electronic Technology

Embedded Computing 2

Outline

The embedded computing space. Platforms: system-on-chip,

networks. Architectures, applications,

methodologies. Standards-based design.

Multiple standards.

Example embedded computing systems

Motorola Siemens

Early history

Late 1940’s: MIT Whirlwind computer was designed for real-time operations. Originally designed to control an aircraft

simulator.

First microprocessor was Intel 4004 in early 1970’s.

HP-35 calculator used several chips to implement a microprocessor in 1972.

Early history, cont’d.

Automobiles used microprocessor-based engine controllers starting in 1970’s. Control fuel/air mixture, engine

timing, etc. Multiple modes of operation: warm-

up, cruise, hill climbing, etc. Provides lower emissions, better fuel

efficiency.

Multiprocessor systems-on-chips

Roughly speaking, system-on-chip with at least two processors.

Usually heterogeneous multiprocessor: CPUs, DSPs, etc. Hardwired accelerators. Mixed-signal front end.

Consumer electronics categories

2001 2002 2003 2004

Satellite TV

$1.18 $1.12 $1.48 $1.89

DVR (40E6)

0.14 0.57 0.18 0.54

DVD 2.1 2.43 2.7 2.46Set-top Internet

0.20 0.12 0.63 0.341

PC (120E6)

12.96 12.61 15.58 17.2

Wall Street Journal/EIA

Consumer electronics prices

Best Buy November 2003:

Characteristics of embedded systems

Very high performance. Vision + compression + speech + networking

all on the same platform.

Multiple task, heterogeneous.Real-time.Often low power.Highly reliable.

I reboot my piano every 4 months, my PC every day.

Mudge et al: Mobile supercomputing

Future mobile platform: Speech recognition. Cryptography. Augmented reality. Typical applications (email, etc.).

Requires 16x 2 GHz Pentium 4. Peak power must not exceed 75 mW.

Assumes 5% battery improvement per year.

Mudge et al: Performance trends for desktop processors

i386 i486 Pentium Pentium Pro Pentium II Pentium III Pentium 4 One Gen Two Gen Three Gen

Technology (relative FO4 delay)

Pipelining (relative FO4 gates/stage)

ILP (relative SPECInt/Mhz)

Performance

Moore's Law Speedup

Performance Gap

10k SPECInt2000

Technology (relative FO4 delay)

Pipelining (relative FO4 gates/stage)

ILP (relative SPECInt/Mhz)

Performance

Moore's Law Speedup

Performance Gap

10k SPECInt2000

Moore's Law Speedup

Performance Gap

10k SPECInt2000

Mudge et al: Power trends for desktop processors

Total Power (W)

Dynamic Power (W)

Static Power (W)

75 mW Peak Power

Power Gap

Total Power (W)

Dynamic Power (W)

Static Power (W)

75 mW Peak Power

Power Gap

Platforms

An architecture that is designed for an application domain: Can be used in several products. Allows customization.

Platforms are often customized for their target audience.

Platforms spread out development costs over more products.

Some people hope for a single universal platform…

Why multiple platforms?

People still care about cost. People care about power

consumption. Sufficiently general solutions don’t

fit on one chip.

Intel IXP2850 network processor

Packet processing, control processing, security.

Software development environment includes simulator.

Xscale

Securityprocessor

16 microengines

TI OMAP

Targets communications, multimedia.

Multiprocessor with DSP, RISC.

C55x DSP

OMAP 5910:

Memory ctrl

MPUinterface

SystemDMA

control

bridge

ST Nomadik

Targets mobile multimedia.

A multiprocessor-of-multiprocessors.

Audioaccelerator

Videoaccelerator

heterogeneousmultiprocessors

ST MMDSP+

Embedded processor core used in multiple chips: Runs at 175 MHz. 1 cycle per instruction. 2-level instruction cache. 16/24-bit fixed point. 32-bit floating point. C programmed Fully synthesizable.

Nomadik video accelerator

MMDSP+data

RAMinstrRAM

Interruptcontroller

Picturepost

processing

Videocodec

Pictureinput

processing

Localdatabus

MasterAHBDMA

Automotive embedded systems

Today’s high-end automobile may have 100 microprocessors: 4-bit microcontroller checks seat

belt; microcontrollers run dashboard

devices; 16/32-bit microprocessor controls

engine.

BMW 850i brake and stability control system

Anti-lock brake system (ABS): pumps brakes to reduce skidding.

Automatic stability control (ASC+T): controls engine to improve stability.

ABS and ASC+T communicate. ABS was introduced first---needed to

interface to existing ABS module.

BMW 850i, cont’d.

sensor

ABShydraulic

The eternal triangle

Hardware and software architectures determine capabilities.

Applications guide design decisions.

Methodologies allow repeatable, predictable design.

architectures

applications

methodologies

Observations and implications

A little domain knowledge helps a lot. The architectural design space is

large and chunky. Less synthesis, more analysis.

IP components must be adapted to play together. Configurable IP, wrappers. Supporting tools (compilers, etc.) must

be adaptable.

Software in consumer devices (ST)

Modern audio standards (Dolby, MP3, etc.):

Modern video standards (MPEG-2, DV, etc.):

1 million lines of code.

2 million lines of code and counting.

Software and MPSoC design

The MPSoC must run the application. Design verification must include the soft

ware running on the hardware. May not know all possible code at desi

gn time. Limits design characterization. Must provide programming environment

MPSoCs and standards

Standards enable large markets. MPSoCs need large markets to justify chip deve

lopment costs, reduce manufacturing overhead.

MPSoCs provide benefits: Low power. High performance.

Meeting the standard requires effort: Platform must allow multiple implementations. Standard is complex and hard to implement.

Design challenges in standards-driven markets

Design and verify methods within the standard. Standards allow differentiation.

Design and verify methods outside the standard’s scope. User interface, etc.

Design and verify interfaces. Within standard, connection to extra-

standard elements.

Standards-based systems

Reference implementation forms a basis for product. Port to platform. Enhance performance, features.

Want to minimize unnecessary changes to the software.

Must make some changes to the software.

Characteristics of reference implementations

The specification does not describe hardware or software.

The spec is in the domain of signal processing, etc.

Designed for and tested on workstations. Infinite memory. Poor cache behavior. Single process. Limited real-time behavior.

The executable spec misrepresents some system properties:

Error handling. Buffer management.

H.264 motion estimation, cont’d.

Multiple reference frames increases accuracy. Handles

occlusion.

Once again, receiver is more complex.

Why are standards so complex?

Algorithm designers like to design algorithms. Standards are

complex.

Standards bodies must embody competing interests, ideas in their standards.

MPEG Tamperemeeting

Design refinement

Bad news: hard to learn the platform in order to

change it.

Good news: an existing design can be measured,

analyzed, and refined.

Worldwide shipping by UPS ...

roughly US$ 50 for CD and US$ 100 for paper copy

(1500 pages, heavy!) Bluetooth.com

Four types of people

Algorithms people. Don’t like programming. Don’t know that hardware exists.

Software people. Don’t like hardware.

Hardware people. Tolerate software. Don’t know applications exist.

Managers. Don’t know anything. Don’t do anything.

Example: MPEG-2 codec

One of the reference MPEG-2 codecs. Simple algorithms.

Designed for workstation operation. Implementers must port to chosen plat

form. Limited memory. Limited CPU.

MPEG-2 porting challenges

Codec uses a mixture of buffering strategies. Some buffers are statically allocated. Some buffers are allocated from the

May need to change number representation. Integer, double-precision, etc.

Error messages use Unix methods.

Example: H.264 codec

Reference encoder is 700,000 lines of C code. Uses simple algorithms.

Supports a wide range of: Display sizes. Features.

H.264 porting challenges

Figure out what code is of interest. Large call graph.

May need to change number representation. Integer, double-precision, etc.

Buffer management. Buffer allocation takes up over 50%

of CPU time.

Multiple standards

Many MPSoCs must implement multiple standards: Communications. Networking. Multimedia. Security.

Requires running a lot of different types of algorithms. Good case for specialization, co-design, configu

rable CPUs, etc. Need some general-purpose computers for loa

d sharing, compatibility.

Platforms, standards, and MPSoCs

A platform allows multiple variations of a system. Well-suited to standards.

Programmability is key to platform-based design.

The design productivity gap

2001 2003 2006 2009

design

Two phases of platform-based design

Semiconductor house designs the platform. Requirements may

come from standards, systems houses.

Systems house uses the platform. May need to start

design before chip is available.

requirements past designs

platform

userneeds

product

Challenges in platform-based design

Don’t have the full application. Must estimate characteristics of part

of the application. Must determine the appropriate

level of programmability. Programmability often costs in area,

power. Must provide programming tools

along with the chip.

Transaction-level modeling is not enough

The MPSoC must run the complete application. Implementing transactions is necessary

but not sufficient. Transactions are relatively short term. SoCs have a lot of state in memory.

Need to thoroughly exercise that state over a long period.

Summary

Chip designers are now system designers. Must deal with hardware and software.

Today’s applications are complex. Reference implementations must be

optimized, extended.

Platforms present challenges for: Hardware designers---characterization,

optimization. Software designers---performance/power

evaluation, debugging.

CD-PLAYER

Compact disc players

Device characteristics.Hardware architectures.Software.

CD audio

44.1 kHz sample rate.16 bit samples.Stereo.Additional data tracks.

Compact disc

Data stored on bottom of disc:

substrate aluminumcoating

plasticcoating

CD medium

Rotational speed: 1.2-1.4 m/s (CLV).Track pitch: 1.6 microns.Diameter: 120 mm.Pit length: 0.8 -3 microns.Pit depth: .11 microns.Pit width: 0.5 microns.Laser wavelength: 780 nm.

CD layout

Data stored in spiral, not concentric circle:

CD mechanism

Laser, lens, sled:

detectorsdiffraction

gratingsled

Laser focus

Focus controlled by vertical position of lens.

Unfocused beam causes irregular spot:

In focusOut of focus Out of focus

Laser pickup

Side spotdetectors

Level:A+B+C+DFocus error:(A+C)-(B+D)Tracking error:E-F

Servo control

Four main signals: focus (laser) @ 245 kHz; tracking (laser) @ 245 kHz; sled (motor): @ 800 Hz; Disc motor.

Optical pickup

Eight-to-fourteen modulation: Fourteen-bit code guarantees a

maximum distance between transitions.

00000011 00100100000000

Error correction

CD capacity: 6.99 GB raw, 700 MB formatted.

Reed-Solomon code: g(x) = (x-) (x- 2) … (x- n-k-1) (x- n-k)

Produces data, erasure bits.Time to solve varies greatly depending on

noise.CD interleaves Reed-Solomon blocks to

reduce effects of large data gaps.

CIRC encoding

Cross-interleaved Reed-Solomon coding. Interleaves to reduce burst errors.

Each 16-bit sample split into two 8-bit symbols.

Specs: Max correctable burst: 4000 bits = 2.5 mm Max interpolatable burst: 12,300 bits = 7.7 m

CIRC algorithm

Sample split into two symbols.Six samples from each channel (=24

symbols) are chosen.Samples are delayed and scrambled.Parity symbols (Q symbols) are generated.Values are delayed by various amounts.P parity symbols are generated.Even words delayed by one symbol, P and Q

words are inverted.Frame = 32 8-bit symbols.

Control word

8-bit control word for every 32-symbol block: P: 1 during music/lead-in, 0 at start of

selection. Q: track number, time, etc (spread over

98 bits). R, S, T, U, V, W: reserved.

Control and error correction

Skips caused by physical disturbance. Wait for disturbance to subside. Retry.

Read errors caused by disc/servo problems. Detect error. Choose location for retry. Retry. Fail and interpolate.

Retry problems

Data is stored in a spiral. Can’t seek track as on magnetic disc. Sled servo is very coarse.

Data is only weakly addressed. Must read data to know where to go.

Audio playback

Audio CD needs no audio processing.Tasks:

convert to analog; amplify.

Digital/analog conversion

1-bit MASH conversion:

interpolationnoise

shapingPWM integrator

Decoding is easier than encoding, but requires: decompression; filtering.

Basic CD standard for data discs.No standards for MP3 disc file

structure: player must understand Windows, Mac, Unix discs.

Jog/skip memory

Read samples into RAM, play back from RAM.

Modern RAMs are larger than needed for reasonable jog/skip.

Jog memory saves some power.

CD/MP3 player

AudioCPU

Jogmemory

Errorcorrector

ServoCPU

Analogin

Analogout

FE, TE, amp

focus,tracking,sled,motor

memory

display

DVD format

Similar to CD, but: shorter wavelength laser; tighter pits; two layers of data.

Audio on DVD

Alternatives: MP3 on data DVD (stereo). Audio track of video DVD (5.1). DVD audio (5.1). SACD (5.1).

Introduction

Object-oriented design.Unified Modeling Language (UML).

System modeling

Need languages to describe systems: useful across several levels of

abstraction; understandable within and between

organizations.Block diagrams are a start, but don’t

cover everything.

Object-oriented design

Object-oriented (OO) design: A generalization of object-oriented programming.

Object = state + methods. State provides each object with its own

identity. Methods provide an abstract interface

to the object.

OO implementation in C++

class display {pixels : pixeltype[IMAX,JMAX];

public:display() { }pixeltype pixel(int i, int j) { return pixels[i,j]; }void set_pixel(pixeltype val, int i, int j) { pixels[i,j] = val; }

OO implementation in C

typedef struct { pixels: pixeltype[IMAX,JMAX]; } display;

display d1;

pixeltype pixelval(pixel *px, int i, int j) { return px[i,j]; }

Objects and classes

Class: object type.Class defines the object’s state

elements but state values may change over time.

Class defines the methods used to interact with all objects of that type. Each object has its own state.

OO design principles

Some objects will closely correspond to real-world objects. Some objects may be useful only for

description or implementation.Objects provide interfaces to

read/write state, hiding the object’s implementation from the rest of the system.

Developed by Booch et al.Goals:

object-oriented; visual; useful at many levels of abstraction; usable for all aspects of design.

UML object

d1: Display

pixels: array[] of pixelselementsmenu_items

pixels is a2-D array

comment

object nameclass name

attributes

UML class

Display

pixelselementsmenu_items

mouse_click()draw_box

operations

class name

The class interface

The operations provide the abstract interface between the class’s implementation and other classes.

Operations may have arguments, return values.

An operation can examine and/or modify the object’s state.

Choose your interface properly

If the interface is too small/specialized: object is hard to use for even one application; even harder to reuse.

If the interface is too large: class becomes too cumbersome for designers

to understand; implementation may be too slow; spec and implementation are probably buggy.

Relationships between objects and classes

Association: objects communicate but one does not own the other.

Aggregation: a complex object is made of several smaller objects.

Composition: aggregation in which owner does not allow access to its components.

Generalization: define one class in terms of another.

Class derivation

May want to define one class in terms of another. Derived class inherits attributes,

operations of base class.

Derived_class

Base_class

UMLgeneralization

Class derivation example

Display

pixelselementsmenu_items

pixel()set_pixel()mouse_click()draw_box

BW_display Color_map_display

baseclass

derived class

Multiple inheritance

Speaker Display

Multimedia_display

base classes

derived class

Links and associations

Link: describes relationships between objects.

Association: describes relationship between classes.

Link example

Link defines the contains relationship:

message

msg = msg1length = 1102

message

msg = msg2length = 2114

message set

count = 2

Association example

message

msg: ADPCM_streamlength : integer

message set

count : integer

0..* 1

contains

# contained messages # containing message sets

Stereotypes

Stereotype: recurring combination of elements in an object or class.

Example: <<foo>>

Behavioral description

Several ways to describe behavior: internal view; external view.

State machines

state state name

transition

Event-driven state machines

Behavioral descriptions are written as event-driven state machines. Machine changes state when receiving

an input.An event may come from inside or

outside of the system.

Types of events

Signal: asynchronous event.Call: synchronized communication.Timer: activated by time.

Signal event

<<signal>>mouse_click

leftorright: buttonx, y: position

declaration

mouse_click(x,y,button)

event description

Call event

draw_box(10,5,3,2,blue)

Timer event

tm(time-value)

Example state machine

regionfound

got menuitem

calledmenu item

foundobject

objecthighlighted

finish

mouse_click(x,y,button)/find_region(region)

input/outputregion = menu/which_menu(i) call_menu(I)

region = drawing/find_object(objid) highlight(objid)

Sequence diagram

Shows sequence of operations over time.

Relates behaviors of multiple objects.

Sequence diagram example

m: Mouse d1: Display u: Menu

mouse_click(x,y,button)which_menu(x,y,i)

call_menu(i)

Summary

Object-oriented design helps us organize a design.

UML is a transportable system design language. Provides structural and behavioral

description primitives.

Models of Computation

Topics

Why models of computation? Structural models. Finite-state machines. Turing machines. Petri nets. Control flow graphs. Data flow models. Task graphs. Control flow models.

Models of computation

Models of computation affect programming style.

No one model of computation is good for all algorithms.

Large systems may require different models of computation for different parts.Models must communicate compatibly.

Processor graph

Finite state machine

State transition graph and table are equivalent:

s1 s20/0

0 s1 s2 0

1 s1 s1 0

0 s2 s2 1

1 s2 s3 0

0 s3 s3 0

1 s3 s1 1

Finite state machine properties

Finite state. Nondeterministic variant.

Nondeterministic FSM

Several transitions out of a state for a given input. Equivalent to executing

all alternatives in parallel.

Can allow moves---goes to next state without input.

s1 s2a

Deterministic FSM from nondeterministic FSM Add states for the v

arious combinations of nondeterminism.

s1 s2a

nondeterministic

s1 s12a

deterministic

1 0 1 0 10 1 0 1 1 0 11 0

Turing machine

General model of computing:

program

Turing machine step

1. Read current square.

2. Erase current square.

3. Take state-dependent action:1. Print new value.

2. Move to adjacent cell.

3. Set machine to next state.

Turing machine properties

Example program: If (state = 2 and cell =

0): print 0, move left, state = 4.

If (state = 2 and cell = 1): print 1, move left, state = 3.

Can be implemented on many physical devices.

Turing machine is a general model of computability.

Can be extended to probabilistic behavior.

Turing machine properties

Infinite tape = infinite state machine. Basic model of computability.

Lambda calculus is alternative model.Other models of computing can be shown to

be equivalent/proper subset of Turing machine.

Control flow graph

Commonly used to model program structure.

x = a - b

i = 0?

y = c + d

CDFG properties

Finite state model. Single thread of control. Can handle subroutines.

Petri net

Parallel model of computation.

token transition

Firing rule

A transition is enabled if each place at its inputs have at least one token.A transition doesn’t have to fire right away.

Firing a transition removes tokens from inputs and adds a token to each output place.

In general, may require multiple tokens to enable.

Properties of Petri nets

Turing complete. Arbitrary number of tokens.

Nondeterministic behavior.Naturally model parallelism.

Task graph

Used to model multi-rate systems.

Task graph properties

Not a Turning machine. No branching behavior. May be extended to provide conditionals.

Possible models of execution time: Constant. Min-max bounds. Statistical.

Can model late arrivals, early departures by adding dummy processes.

Data flow graph

Partially-ordered computations:

+ -, *

+, -, *

-, +, *

Data flow streams

Captures sequence but not time. Totally-ordered set of values.

New values are appended at the end as they appear.

May be infinite.

88 -23 7 44 9 -28 -44 88 -23 7 44 9

Firing rules

A node may have one or more firing rules.

Firing rules determine when tokens are consumed and produced.Firing consumes a set of tokens at inputs,

generates token at output.

Example firing rules

Basic rule fires when tokens are available at all inputs:

Conditional firing rule depends on control input:

Data flow graph properties

Finite state model. Basic data flow graph is acyclic. Scheduling provides a total ordering of

operations.

Synchronous data flow

Lee/Messerschmitt: Relate data flow graph properties to schedulability.Synchronous communication between data flo

w nodes.Nodes may communicate at multiple rates.

SDF notation

Nodes may have rates at which data are produced nor consumed.

Edges may have delays.

+ -1 2

SDF example

This graph has consistent sample rates:

+ +2 1

separateoutputs

Delays in SDF graphs

Delays do not change rates, only the amount of data stored in the system.

Changes system start-up.

+ -1 2

Kahn process network

Process has unbounded FIFO at each input:

Each channel carries a possibly infinite sequence or stream. A process maps one or more input sequences to one or more output sequences.

processchannel

Properties of processes

Processes are usually required to be continuous: least upper boundedness can be moved across function boundary.

Monotonicity:X in X’ => F(X) in F(X’)

Networks of processes

A network of processes relates the streams of several processes.

If I = input sequences, X = internal sequences + outputs, then network behavior fixed point isX = F(X,I)

Network properties

A network of monotonic processes is a monotonic process.Even in the presence of feedback loops.

Can add nondeterminism in several ways:allow process to test for emptiness;allow process to be internally nondeterminate;allow more than one process to consume data from a c

hannel;etc.

Statecharts

Ancestor of UML state diagrams. Provided composite states:

OR states;AND states.

Composite states reduce the size of the state transition graph.

Statechart OR state

traditional

OR state

Statechart AND state

S1-3 S1-4

S2-3 S2-4

traditional

S5AND state

TCAS II specification

TCAS II: aircraft collision avoidance system.

Monitors aircraft and air traffic info. Provides audio warnings and directives to

avoid collisions. Leveson et al used RMSL language to cap

ture the TCAS specification.

State description: Transition bus for transitions between many states:state1

inputs

state description

outputs

TCAS top-level descriptionCAS

power-offpower-onInputs:TCAS-operational-status {operational,not-operational}

fully-operationalC

standby

own-aircraft

other-aircraft i:[1..30]

mode-s-ground-station i:[1..15]

Own-Aircraft AND stateCAS

Inputs:own-alt-radio: integer standby-discrete-input: {true,false}own-alt-barometric:integer, etc.

Effective-SL Alt-SL Alt-layer Climb-inibit Descend-inibit

Increase-climb-inibit

Increase-Descend-inibit

Advisory-Status

... ......

......

Outputs:sound-aural-alarm: {true,false} aural-alarm-inhibit: {true, false}combined-control-out: enumerated, etc.

Computers as Components Principles of Embedded Computing System Design Dr. Prof. Huang Tingle Group...

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