VHDL : Programming By Example

476 Pages·2002·11.06 MB·English

by  Perry, Douglas L

VHDL:
Programming
by Example
Douglas L. Perry
Fourth Edition
McGraw-Hill
New York • Chicago • San Francisco • Lisbon • London
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CONTENTS
Foreword xiii
Preface xv
Acknowledgments xviii
Chapter 1 Introduction to VHDL 1
VHDL Terms 2
Describing Hardware in VHDL 3
Entity 3
Architectures 4
Concurrent Signal Assignment 5
Event Scheduling 6
Statement Concurrency 6
Structural Designs 7
Sequential Behavior 8
Process Statements 9
Process Declarative Region 9
Process Statement Part 9
Process Execution 10
Sequential Statements 10
Architecture Selection 11
Configuration Statements 11
Power of Configurations 12
Chapter 2 Behavioral Modeling 15
Introduction to Behavioral Modeling 16
Transport Versus Inertial Delay 20
Inertial Delay 20
Transport Delay 21
Inertial Delay Model 22
Transport Delay Model 23
Simulation Deltas 23
Drivers 27
Driver Creation 27
Bad Multiple Driver Model 28
Generics 29
Block Statements 31
Guarded Blocks 35
vi Contents
Chapter 3 Sequential Processing 39
Process Statement 40
Sensitivity List 40
Process Example 40
Signal Assignment Versus Variable Assignment 42
Incorrect Mux Example 43
Correct Mux Example 45
Sequential Statements 46
IF Statements 47
CASE Statements 48
LOOP Statements 50
NEXT Statement 53
EXIT Statement 54
ASSERT Statement 56
Assertion BNF 57
WAIT Statements 59
WAIT ON Signal 62
WAIT UNTIL Expression 62
WAIT FOR time_expression 62
Multiple WAIT Conditions 63
WAIT Time-Out 64
Sensitivity List Versus WAIT Statement 66
Concurrent Assignment Problem 67
Passive Processes 70
Chapter 4 Data Types 73
Object Types 74
Signal 74
Variables 76
Constants 77
Data Types 78
Scalar Types 79
Composite Types 86
Incomplete Types 98
File Types 102
File Type Caveats 105
Subtypes 105
Chapter 5 Subprograms and Packages 109
Subprograms 110
Function 110
Contents vii
Conversion Functions 113
Resolution Functions 119
Procedures 133
Packages 135
Package Declaration 136
Deferred Constants 136
Subprogram Declaration 137
Package Body 138
Chapter 6 Predefined Attributes 143
Value Kind Attributes 144
Value Type Attributes 144
Value Array Attributes 147
Value Block Attributes 149
Function Kind Attributes 151
Function Type Attributes 151
Function Array Attributes 154
Function Signal Attributes 156
Attributes ’EVENT and ’LAST_VALUE 157
Attribute ’LAST_EVENT 158
Attribute ’ACTIVE and ’LAST_ACTIVE 160
Signal Kind Attributes 160
Attribute ’DELAYED 161
Attribute ’STABLE 164
Attribute ’QUIET 166
Attribute ’TRANSACTION 168
Type Kind Attributes 169
Range Kind Attributes 170
Chapter 7 Configurations 173
Default Configurations 174
Component Configurations 176
Lower-Level Configurations 179
Entity-Architecture Pair Configuration 180
Port Maps 181
Mapping Library Entities 183
Generics in Configurations 185
Generic Value Specification in Architecture 188
Generic Specifications in Configurations 190
Board-Socket-Chip Analogy 195
Block Configurations 199
Architecture Configurations 201
viii Contents
Chapter 8 Advanced Topics 205
Overloading 206
Subprogram Overloading 206
Overloading Operators 210
Aliases 215
Qualified Expressions 215
User-Defined Attributes 218
Generate Statements 220
Irregular Generate Statement 222
TextIO 224
Chapter 9 Synthesis 231
Register Transfer Level Description 232
Constraints 237
Timing Constraints 238
Clock Constraints 238
Attributes 239
Load 240
Drive 240
Arrival Time 240
Technology Libraries 241
Synthesis 243
Translation 243
Boolean Optimization 244
Flattening 245
Factoring 246
Mapping to Gates 247
Chapter 10 VHDL Synthesis 251
Simple Gate—Concurrent Assignment 252
IF Control Flow Statements 253
Case Control Flow Statements 256
Simple Sequential Statements 257
Asynchronous Reset 259
Asynchronous Preset and Clear 261
More Complex Sequential Statements 262
Four-Bit Shifter 264
State Machine Example 266
Contents ix
Chapter 11 High Level Design Flow 273
RTL Simulation 275
VHDL Synthesis 277
Functional Gate-Level Verification 283
Place and Route 284
Post Layout Timing Simulation 286
Static Timing 287
Chapter 12 Top-Level System Design 289
CPU Design 290
Top-Level System Operation 290
Instructions 291
Sample Instruction Representation 292
CPU Top-Level Design 293
Block Copy Operation 299
Chapter 13 CPU: Synthesis Description 303
ALU 306
Comp 309
Control 311
Reg 321
Regarray 322
Shift 324
Trireg 326
Chapter 14 CPU: RTL Simulation 329
Testbenches 330
Kinds of Testbenches 331
Stimulus Only 333
Full Testbench 337
Simulator Specific 340
Hybrid Testbenches 342
Fast Testbench 345
CPU Simulation 349
Chapter 15 CPU Design: Synthesis Results 357
x Contents
Chapter 16 Place and Route 369
Place and Route Process 370
Placing and Routing the Device 373
Setting up a project 373
Chapter 17 CPU: VITAL Simulation 379
VITAL Library 381
VITAL Simulation Process Overview 382
VITAL Implementation 382
Simple VITAL Model 383
VITAL Architecture 386
Wire Delay Section 386
Flip-Flop Example 388
SDF File 392
VITAL Simulation 394
Back-Annotated Simulation 397
Chapter 18 At Speed Debugging Techniques 399
Instrumentor 401
Debugger 401
Debug CPUDesign 401
Create Project 402
Specify Top-Level Parameters 403
Specify Project Parameters 403
Instrument Signals 404
Write Instrumented Design 405
Implement New Design 405
Start Debug 406
Enable Breakpoint 406
Trigger Position 408
Waveform Display 408
Set Watchpoint 409
Complex Triggers 410
Appendix A Standard Logic Package 413
Appendix B VHDL Reference Tables 435
Appendix C Reading VHDL BNF 445
Contents xi
Appendix D VHDL93 Updates 449
Alias 449
Attribute Changes 450
Bit String Literal 452
DELAY_LENGTH Subtype 452
Direct Instantiation 452
Extended Identifiers 453
File Operations 454
Foreign Interface 455
Generate Statement Changes 456
Globally Static Assignment 456
Groups 457
Incremental Binding 458
Postponed Process 459
Pure and Impure Functions 460
Pulse Reject 460
Report Statement 461
Shared Variables 461
Shift Operators 463
SLL—shift left logical 463
SRL—shift right logical 463
SLA—shift left arithmetic 463
SRA—shift right arithmetic 463
ROL—rotate left 464
ROR—rotate right 464
Syntax Consistency 464
Unaffected 466
XNOR Operator 466
Index 469
About the Author 477
PREFACE
This is the fourth version of the book and this version now not only provides
VHDLlanguage coverage but design methodology information as well. This
version will guide the reader through the process of creating a VHDL
design, simulating the design, synthesizing the design, placing and routing
the design, using VITAL simulation to verify the final result, and a new
technique called At-Speed debugging that provides extremely fast design
verification. The design example in this version has been updated to reflect
the new focus on the design methodology.
This book was written to help hardware design engineers learn how to
write good VHDLdesign descriptions. The goal is to provide enough VHDL
and design methodology information to enable a designer to quickly write
good VHDLdesigns and be able to verify the results. It will also attempt
to bring the designer with little or no knowledge of VHDL, to the level of
writing complex VHDLdescriptions. It is not intended to show every pos-
sible construct of VHDLin every possible use, but rather to show the de-
signer how to write concise, efficient, and correct VHDL descriptions of
hardware designs.
This book is organized into three logical sections. The first section of the
book will introduce the VHDLlanguage, the second section walks through
a VHDL based design process including simulation, synthesis, place and
route, and VITALsimulation; and the third section walks through a design
example of a small CPU design from VHDL capture to final gate-level
implementation, and At-Speed debugging. At the back of the book are
included a number of appendices that contain useful information about the
language and examples used throughout the book.
In the first section VHDLfeatures are introduced one or more at a time.
As each feature is introduced, one or more real examples are given to show
how the feature would be used. The first section consists of Chapters 1
through 8, and each chapter introduces a basic description capability of
VHDL. Chapter 1 discusses how VHDLdesign relates to schematic based
design, and introduces the basic terms of the language. Chapter 2 describes
some of the basic concepts of VHDL, including the different delay mecha-
nisms available, how to use instance specific data, and defines VHDLdri-
vers. Chapter 2 discusses concurrent statements while Chapter 3 introduces
the reader to VHDLsequential statements. Chapter 4 talks about the wide