VHDL for Logic Synthesis, 3rd Edition

Preface xi

List of Figures xv

List of Tables xvii

1 Introduction 1

1.1 The VHDL Design Cycle 1

1.2 The Origins of VHDL 2

1.3 The Standardisation Process 3

1.4 Unification of VHDL Standards 4

1.5 Portability 4

2 Register-Transfer Level Design 7

2.1 The RTL Design Stages 8

2.2 Example Circuit 8

2.3 Identify the Data Operations 10

2.4 Determine the Data Precision 12

2.5 Choose Resources to Provide 12

2.6 Allocate Operations to Resources 13

2.7 Design the Controller 14

2.8 Design the Reset Mechanism 15

2.9 VHDL Description of the RTL Design 15

2.10 Synthesis Results 16

3 Combinational Logic 19

3.1 Design Units 19

3.2 Entities and Architectures 20

3.3 Simulation Model 22

3.4 Synthesis Templates 25

3.5 Signals and Ports 27

3.6 Initial Values 29

3.7 Simple Signal Assignments 30

3.8 Conditional Signal Assignments 31

3.9 Selected Signal Assignment 33

3.10 Worked Example 34

4 Basic Types 37

4.1 Synthesisable Types 37

4.2 Standard Types 37

4.3 Standard Operators 38

4.4 Type Bit 39

4.5 Type Boolean 39

4.6 Integer Types 41

4.7 Enumeration Types 46

4.8 Multi-Valued Logic Types 47

4.9 Records 48

4.10 Arrays 49

4.11 Aggregates, Strings and Bit-Strings 53

4.12 Attributes 56

4.13 More on Selected Signal Assignments 60

5 Operators 63

5.1 The Standard Operators 63

5.2 Operator Precedence 64

5.3 Boolean Operators 70

5.4 Comparison Operators 73

5.5 Shifting Operators 76

5.6 Arithmetic Operators 79

5.7 Concatenation Operator 84

6 Synthesis Types 85

6.1 Synthesis Type System 85

6.2 Making the Packages Visible 87

6.3 Logic Types – Std_Logic_1164 90

6.4 Numeric Types – Numeric_Std 95

6.5 Fixed-Point Types – Fixed_Pkg 105

6.6 Floating-Point Types – Float_Pkg 119

6.7 Type Conversions 134

6.8 Constant Values 144

6.9 Mixing Types in Expressions 146

6.10 Top-Level Interface 147

7 Std_Logic_Arith 151

7.1 The Std_Logic_Arith Package 151

7.2 Contents of Std_Logic_Arith 152

7.3 Type Conversions 161

7.4 Constant Values 162

7.5 Mixing Types in Expressions 164

8 Sequential VHDL 167

8.1 Processes 167

8.2 Signal Assignments 170

8.3 Variables 171

8.4 If Statements 172

8.5 Case Statements 177

8.6 Latch Inference 178

8.7 Loops 181

8.8 Worked Example 187

9 Registers 191

9.1 Basic D-Type Register 191

9.2 Simulation Model 192

9.3 Synthesis Model 193

9.4 Register Templates 195

9.5 Register Types 199

9.6 Clock Types 199

9.7 Clock Gating 200

9.8 Data Gating 201

9.9 Asynchronous Reset 203

9.10 Synchronous Reset 208

9.11 Registered Variables 210

9.12 Initial Values 211

10 Hierarchy 213

10.1 The Role of Components 213

10.2 Indirect Binding 214

10.3 Direct Binding 219

10.4 Component Packages 220

10.5 Parameterised Components 222

10.6 Generate Statements 225

10.7 Worked Examples 230

11 Subprograms 243

11.1 The Role of Subprograms 243

11.2 Functions 243

11.3 Operators 254

11.4 Type Conversions 258

11.5 Procedures 261

11.6 Declaring Subprograms 267

11.7 Worked Example 270

12 Special Structures 279

12.1 Tristates 279

12.2 Finite State Machines 284

12.3 RAMs and Register Banks 292

12.4 Decoders and ROMs 297

13 Test Benches 301

13.1 Test Benches 301

13.2 Combinational Test Bench 302

13.3 Verifying Responses 305

13.4 Clocks and Resets 307

13.5 Other Standard Types 310

13.6 Don’t Care Outputs 312

13.7 Printing Response Values 314

13.8 Using TextIO to Read Data Files 315

13.9 Reading Standard Types 318

13.10 TextIO Error Handling 319

13.11 TextIO for Synthesis Types 321

13.12 TextIO for User-Defined Types 322

13.13 Worked Example 325

14 Libraries 327

14.1 The Library 327

14.2 Library Names 328

14.3 Library Work 329

14.4 Standard Libraries 330

14.5 Organising Your Files 333

14.6 Incremental Compilation 335

15 Case Study 337

15.1 Specification 337

15.2 System-Level Design 338

15.3 RTL Design 340

15.4 Trial Synthesis 352

15.5 Testing the Design 353

15.6 Floating-Point Version 361

15.7 Final Synthesis 362

15.8 Generic Version 364

15.9 Conclusions 366

Appendix A Package Listings 369

A.1 Package Standard 369

A.2 Package Standard_Additions 373

A.3 Package Std_Logic_1164 380

A.4 Package Std_Logic_1164_Additions 383

A.5 Package Numeric_Std 389

A.6 Package Numeric_Std_Additions 393

A.7 Package Fixed_Float_Types 400

A.8 Package Fixed_Pkg 401

A.9 Package Float_Pkg 415

A.10 Package TextIO 429

A.11 Package Standard_Textio_Additions 431

A.12 Package Std_Logic_Arith 432

A.13 Package Math_Real 436

Appendix B Syntax Reference 439

B.1 Keywords 439

B.2 Design Units 440

B.3 Concurrent Statements 441

B.4 Sequential Statements 443

B.5 Expressions 444

B.6 Declarations 445

References 449

Index 451