An Introduction to the Digital Design Process

Arturo Díaz-PérezDepartamento de Computación

Laboratorio de Tecnologías de InformaciónCINVESTAV-IPN

The Design Process

CPUMem I/O

Control

DatapathReg.File

ALU

shift

er

src1src2

dst

The Design Process, cont.

adde

ra 32

32b32 c

HAa0b0

FAa1b1

FAa31b31

s0

s1

s31cout

The Design Process, cont.

sum

cout

ab

cin

in1

in2out

Vcc

Abstraction Hierarchy

A set of interrelated representation levels thatallow a system to be represented in varyingamounts of detail Top

Level 1

Level iLevel i+1

Level N

Botton

Detailvaries Transformation

Design Environment

Behavioral Design

Datapath Design

Logic Design

Physical Design

Manufacturing

Design Idea

Chip or Board

Flow Graph, Pseudo Code, ...

Bus & Register Structure.

Gate Wirelist, Netlist.

Transistor List, Layout,...

Datapath Representation

Procedurefor Controlof Movementof DataBetweenRegistersandBuses

MAINLOGICUNIT

REG2REG1

REG3

LOGIC

DATA CONTROL

Design Procedure

Design: a series of transformation from one representation of a system to another until a representation exists that can be fabricated.

Synthesis: The process of transforming one representation in the design abstraction hierarchy to another representation.

At each levelDesign entrySimulationSynthesisTest generation

Design automation helps transforming one format to another

Types of Descriptions

Behavioral domain: A domain in which a component is described by defining its input/output response.

Algorithmic: a procedure or program to model the behavior of the device without implying any particular physical implementation.

Dataflow: a model in which the data dependencies in the description match those in a real implementation.

Structural domain: A domain in which a component is described in terms of an interconnection of more primitive components.

Pictorial vs. Textual Representation

CCT full_adder( a, b, c, s, c0 )XOR( RISE = 16, FALL = 12 )

g1( w1, a, b )g5( s, w1, c )

NAND( RISE4 = 12, FALL = 10 )g2( w2, c, b );g3( w3, c, a );g4( w4, b, a );g6( c0, w3, w4, w5 );

INPUT a, b, clWIRE w1, w2, w3, w4;OUTPUT s, c0;END CIRCUIT full_adder

s

c0

a

b

c

w1

w2

w3

w4

g1

g2

g3

g4

g5

g6

Textual Representation

Hardware description language: A high level programming language withspecialized constructs for modelinghardware.

Text is better for representation forrepresenting complex behavior; picturesare better for illustrating interrelationships.

CAD Tools

CAD ToolsCAD Tools

EditorEditor Checker/AnalyzerChecker/Analyzer Optimizer/SynthesizerOptimizer/SynthesizerSimulatorSimulator

TextText GraphicsGraphics StochasticStochastic DeterministicDeterministic

NaturalLanguageNatural

LanguageComputerLanguage

ComputerLanguage

Editors

Textual: Spice, VHDL.

Graphics: schematic capture.A library of primitive symbols including a simulation model to each primitive: native or standar parts families: TTL, CMOS, etc.

A system of graphic windows which can be used to create an interconnect of graphic tokens.

Commands for creating wirelists: to physically build the circuit or to test circuit response.

Simulation Tools

Simulator: A program which models the response of a system to input stimuli

Behavioral Design

Datapath Design

Logic Design

Physical Design

Manufacturing

Chip or Board

Flow Graph, Pseudo Code, ...

Bus & Register Structure.

Gate Wirelist, Netlist.

Transistor List, Layout,...

Behavioral Simulator

Datapath Simulator

Gate Level Simulator

Device Simulator

Final TestingProduct sample

Design IdeaSimulation Tools

Oblivious Simulation

1

2

3

4

5

6

7

a

b

z

GATE FUNCTION INPUT1 INPUT2 OUTPUT

1234567

InputInputNOTNOTANDANDOR

ab21145

----326

0011000

Event Driven Simulation

Event driven simulation requires a linked listdata structureEvaluate circuit only when events occurOffers a faster simulation for digital circuitsVHDL is an event driven simulation

- Inp 0

1

- Inp 0

2

- Not 0

3

- Not 0

4

And 0

5

And 0

6Or 0

7

a

b

Simulator Organization

TimeQueueTimeQueue

SignalTracer

SignalTracer

TimeQueue

Processor

TimeQueue

ProcessorProcessorExecutor

ProcessorExecutor

InsertandDelete

events activate

scheduler

Simulation System

TextEditorText

Editor

AnalyzerAnalyzer

DesignLibrary(IMF)

DesignLibrary(IMF)

SchematicEditor

SchematicEditor

ModelBuilderModelBuilder SimulateSimulate

VHDL SourceAnalyzerErrorMessages

Run timeerror messages

Simulation ResultsOther tools

Synthesis Tools

Synthesizer: A computer program thatautomatically performs a translation from one designrepresentation to another or a program that assists a human in making hte translation.

Ideally a behavioral description is synthesized to a layout (silicon compiler).

Most current tools transform data path to gate list.

Synthesis

Behavioral Design

Datapath Design

Logic Design

Physical Design

Manufacturing

Design Idea

Chip or Board

Flow Graph, Pseudo Code, ...

Bus & Register Structure.

Gate Wirelist, Netlist.

Transistor List, Layout,...

2

1

4

35

6

Synthesis Tools

Synthesis Tools

High level synthesizers:AlgorithmicDataflowBehavioral

Low level synthesizers:logic: structural gate level to circuit or layout.algebraic: behavioral gate level to structural gate level or layout.silicon compilers: gate level to layout level.

Summary

Design process is a series of transformations from one representation to another until until a lowlevel representation is achieved:

behavioral, datapath, logic, physical and manufacturing.

Synthesis is the process of transforming one representation in the design abstraction hierarchy to another representation.Two basic ways of description: structural and behavioral.Two basic ways for design entrying: graphical and textual.HDL: a high level programming language with specialized constructs for modeling hardware.CAD tools are used at any level of the design process:

editors, simulators, analyzers/checkers, and synthesizers/optimizers.