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ModelSim®/Questa® Core Advanced Topics

Student Workbook

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Table of Contents

ModelSim/Questa Core Advanced Topics

I

Module 1: Introduction: Functional Verification Overview ............................. 13

Objectives ........................................................................................................................................... 14

Module Overview ............................................................................................................................... 15

2-Day Course Agenda ........................................................................................................................ 16

Digital Simulation Design Flow ......................................................................................................... 17

Functional Verification ...................................................................................................................... 18

Digital Functional Verification .......................................................................................................... 19

Functional Verification Techniques ................................................................................................... 20

Hardware Assisted Functional Verification ....................................................................................... 21

Digital Simulation Using ModelSim / Questa Core ........................................................................... 22

Summary ............................................................................................................................................ 24

Module 2: Tcl/Tk Overview.................................................................................. 25

Objectives ........................................................................................................................................... 26

Module Overview ............................................................................................................................... 27

Why Tcl/Tk? ...................................................................................................................................... 28

Some Examples of Using Tcl/Tk in Debugging ................................................................................ 29

Tcl Overview ...................................................................................................................................... 30

Tk Overview ....................................................................................................................................... 31

Tcl Commands ................................................................................................................................... 32

Basic Tcl Syntax ................................................................................................................................. 33

Tcl Variables ...................................................................................................................................... 34

Command Substitution ....................................................................................................................... 35

Quotes ................................................................................................................................................. 36

Curly Braces ....................................................................................................................................... 37

Table of Contents

ModelSim/Questa Core Advanced Topics

II

Control Structures .............................................................................................................................. 38

Simulation Commands ....................................................................................................................... 39

Using Commands to Add Signals to the Wave Window ................................................................... 40

Using Commands to Organize Signals in the Wave Window ........................................................... 41

Grouping Signals in the Wave Window ............................................................................................. 42

Tcl Script Example ............................................................................................................................. 43

Creating a Simulation Script .............................................................................................................. 44

Simulation Script Example ................................................................................................................. 45

Tk Widget Overview .......................................................................................................................... 46

Tk Commands .................................................................................................................................... 47

Simple Tk Example ............................................................................................................................ 48

Adding a Customized Button to the Main Window ........................................................................... 49

Additional Tcl/Tk Resources ............................................................................................................. 51

Summary ............................................................................................................................................ 52

Lab 1: Tcl/Tk Application .................................................................................................................. 53

Module 3: Code Coverage .................................................................................... 55

Objectives ........................................................................................................................................... 56

Code Coverage ................................................................................................................................... 57

Purpose of Code Coverage ................................................................................................................. 58

Code Coverage in ModelSim / Questa Core ...................................................................................... 59

Types of Code Coverage .................................................................................................................... 60

Unified Coverage Database (UCDB) ................................................................................................. 62

Coverage Modes ................................................................................................................................. 63

Statement Coverage ............................................................................................................................ 64

Table of Contents

ModelSim/Questa Core Advanced Topics

III

Branch Coverage ................................................................................................................................ 65

Expression Coverage .......................................................................................................................... 67

Condition Coverage ............................................................................................................................ 68

Focused Expression Coverage............................................................................................................ 70

Toggle Coverage ................................................................................................................................ 72

Extended Toggle Coverage ................................................................................................................ 73

Finite State Machine (FSM) Coverage ............................................................................................... 74

Invoking Code Coverage: Two-Step Flow ......................................................................................... 75

Invoking Code Coverage: Alternative Two-Step Flows .................................................................... 76

Invoking Code Coverage: Three-Step Flows ..................................................................................... 77

Union of Coverage Types .................................................................................................................. 79

Enabling Code Coverage in the GUI, 2-Step Flow ............................................................................ 80

Enabling Code Coverage in the GUI, 3-Step Flow ............................................................................ 81

Code Coverage Windows ................................................................................................................... 82

Code Coverage in the Structure Window ........................................................................................... 83

Code Coverage Analysis Window ..................................................................................................... 84

Viewing Toggle Coverage.................................................................................................................. 88

Toggle Coverage Data ........................................................................................................................ 89

Instance Coverage Window ............................................................................................................... 91

Code Coverage in the Source Window .............................................................................................. 92

Excluding Lines and Files From Coverage Statistics ......................................................................... 95

Saving and Recalling Exclusions ....................................................................................................... 96

Creating Coverage Reports ................................................................................................................ 97

Saving Coverage Data ........................................................................................................................ 98

Reloading Coverage Data in the GUI .............................................................................................. 100

Table of Contents

ModelSim/Questa Core Advanced Topics

IV

Merging Coverage Data in the GUI ................................................................................................. 102

Invoking Coverage View Mode in the GUI ..................................................................................... 103

Coverage View Mode with UCDB Loaded ..................................................................................... 104

Generating HTML Reports .............................................................................................................. 105

Managing Coverage Data ................................................................................................................. 107

Managing Coverage Data Off-Line .................................................................................................. 109

Understanding Optimization Effects ................................................................................................ 111

Customizing the Optimization Level for Coverage ......................................................................... 112

Coverage Optimization Levels ......................................................................................................... 113

Summary .......................................................................................................................................... 114

Lab 2: Code Coverage ...................................................................................................................... 115

Module 4: vopt for Performance ........................................................................ 117

Objectives ......................................................................................................................................... 118

Module Overview ............................................................................................................................. 119

Optimization (vopt) .......................................................................................................................... 120

vopt — The Big Picture ................................................................................................................... 121

Default Performance Mode .............................................................................................................. 122

Preserving Visibility and Enabling Access ...................................................................................... 123

Design Optimization and Visibility .................................................................................................. 125

Adjusting Design Visibility Through the GUI ................................................................................. 126

Design Visibility versus Performance .............................................................................................. 129

3-Step vopt Flow .............................................................................................................................. 130

2-Step vopt Flow .............................................................................................................................. 131

1-Step vopt Flow .............................................................................................................................. 132

Table of Contents

ModelSim/Questa Core Advanced Topics

V

vopt: Use for Different Flows .......................................................................................................... 134

Lab 3: vopt for Performance ............................................................................................................ 135

Module 5: Optimization Flows and Methods ................................................... 137

Objectives ......................................................................................................................................... 138

Module Overview ............................................................................................................................. 139

ModelSim / Questa Core Structure and Flow .................................................................................. 140

Optimization Flow ............................................................................................................................ 141

RTL/Behavioral Designs .................................................................................................................. 142

vopt Commands for RTL Simulation ............................................................................................... 143

Verilog Delay Modes ....................................................................................................................... 144

Verilog Delay Mode for Gate-Level Simulation .............................................................................. 145

Verilog Gate-Level Without SDF .................................................................................................... 148

Verilog Gate-Level With SDF ......................................................................................................... 149

vopt Switches for Gate-Level Simulation ........................................................................................ 150

Increasing Verilog Gate-Level Optimizations ................................................................................. 152

Analyzing Cell Optimization Results ............................................................................................... 154

Compiled SDF .................................................................................................................................. 156

Verilog Coding Style for Maximum Performance ........................................................................... 157

Direct Programming Interface .......................................................................................................... 159

vcom Performance Commands ........................................................................................................ 160

VHDL Coding for Performance ....................................................................................................... 161

Measuring Time and Memory Usage ............................................................................................... 164

Alternate Elaboration Flow .............................................................................................................. 165

When to Use an Elaboration File ..................................................................................................... 167

Table of Contents

ModelSim/Questa Core Advanced Topics

VI

Tips for Performance ........................................................................................................................ 168

General Performance Issues ............................................................................................................. 170

Summary .......................................................................................................................................... 171

Module 6: Statistical and Memory Profiler ...................................................... 173

Objectives ......................................................................................................................................... 174

Module Overview ............................................................................................................................. 175

Challenges ........................................................................................................................................ 176

Statistical and Memory Profilers ...................................................................................................... 177

Statistical Sampling Profiler ............................................................................................................. 178

Invoking the Profiler ........................................................................................................................ 179

Profile Commands ............................................................................................................................ 181

Enable Profiling ................................................................................................................................ 182

Graphical Views ............................................................................................................................... 183

Understanding In and Under ............................................................................................................ 184

Graphical Views ............................................................................................................................... 186

Profile Details Window .................................................................................................................... 188

Integration With the Source Window ............................................................................................... 189

Saving a Profile Report File ............................................................................................................. 190

Memory Allocation Profiler ............................................................................................................. 191

Capacity Analysis ............................................................................................................................. 192

Displaying Capacity Objects in the Wave Window ......................................................................... 194

Summary .......................................................................................................................................... 195

Lab 4: Analyzing Performance ........................................................................................................ 196

Module 7: Virtual Objects and Signal Spy ....................................................... 197

Table of Contents

ModelSim/Questa Core Advanced Topics

VII

Objectives ......................................................................................................................................... 198

Module Overview ............................................................................................................................. 199

Virtual Objects ................................................................................................................................. 200

Virtual Signals .................................................................................................................................. 201

Create Meaningful Definitions With Virtual Signals ....................................................................... 203

Combining Signals ........................................................................................................................... 204

Extract/Pad or Split Bus ................................................................................................................... 205

Virtual Regions ................................................................................................................................ 206

Virtual Functions .............................................................................................................................. 207

Virtual Signal Builder ...................................................................................................................... 210

Virtual Types .................................................................................................................................... 211

Other Virtual Commands ................................................................................................................. 212

User-Defined Radices ...................................................................................................................... 214

Managing Radices ............................................................................................................................ 216

Global Signal Radix ......................................................................................................................... 217

Virtual Signal Builder ...................................................................................................................... 218

Signal Spy ........................................................................................................................................ 219

init_signal_spy Procedure ................................................................................................................ 221

enable_signal_spy Procedure ........................................................................................................... 222

disable_signal_spy Procedure .......................................................................................................... 223

init_signal_spy VHDL Utility .......................................................................................................... 224

Probing Verilog Signals From the VHDL Testbench ...................................................................... 226

$init_signal_spy Verilog Task ......................................................................................................... 227

VHDL Extended and Verilog Escaped Identifiers ........................................................................... 232

Summary .......................................................................................................................................... 234

Table of Contents

ModelSim/Questa Core Advanced Topics

VIII

Lab 5: Signal Spy ............................................................................................................................. 235

Module 8: Waveform Compare ......................................................................... 237

Objectives ......................................................................................................................................... 238

Module Overview ............................................................................................................................. 239

Saving Waveform Datasets .............................................................................................................. 240

Opening Datasets .............................................................................................................................. 241

Managing Datasets ........................................................................................................................... 242

Dataset and Compare Windows ....................................................................................................... 243

Compare Datasets Using Waveform Compare ................................................................................ 244

Comparison Wizard .......................................................................................................................... 246

Waveform Compare Menus ............................................................................................................. 248

Compare by Signal Dialog Box ....................................................................................................... 249

Compare by Region Dialog Box ...................................................................................................... 250

Add Clocks Dialog Box ................................................................................................................... 251

Differences ....................................................................................................................................... 252

Clocked versus Continuous Differences .......................................................................................... 253

Compare Objects in the List Window .............................................................................................. 254

Write Report ..................................................................................................................................... 255

Save Differences .............................................................................................................................. 256

Save Rules ........................................................................................................................................ 257

Comparing Hierarchical and Flattened Designs ............................................................................... 258

Using Tcl Commands to Define a Comparison ............................................................................... 259

Tcl Compare Command ................................................................................................................... 260

Tcl Compare Example ...................................................................................................................... 261

Table of Contents

ModelSim/Questa Core Advanced Topics

IX

Tcl Compare Example Using "when" .............................................................................................. 263

Summary .......................................................................................................................................... 265

Lab 6: Waveform Compare .............................................................................................................. 266

Module 9: HDL Support and Gate-Level Simulation ...................................... 267

Objectives ......................................................................................................................................... 268

Module Overview ............................................................................................................................. 269

VHDL Support ................................................................................................................................. 270

VHDL-2008 Functionality ............................................................................................................... 271

VHDL VITAL SDF ......................................................................................................................... 272

SDF Annotation ................................................................................................................................ 274

Verilog Support ................................................................................................................................ 275

SystemVerilog .................................................................................................................................. 276

Why SystemVerilog? ....................................................................................................................... 277

SystemVerilog Support .................................................................................................................... 278

SystemVerilog Compilation Units ................................................................................................... 279

SystemVerilog Functionality ............................................................................................................ 280

Summary .......................................................................................................................................... 281

Lab 7: Gate-Level Simulation .......................................................................................................... 282

Module 10: FSM Viewer ..................................................................................... 283

Objectives ......................................................................................................................................... 284

Module Overview ............................................................................................................................. 285

FSM Recognition ............................................................................................................................. 286

FSM Viewer Modes ......................................................................................................................... 287

FSM Recognition in the Transcript Window ................................................................................... 288

Table of Contents

ModelSim/Questa Core Advanced Topics

X

Viewing FSM Information in the GUI ............................................................................................. 289

FSM List Window Menu .................................................................................................................. 290

FSM Viewer and Wave Windows .................................................................................................... 291

FSM Properties ................................................................................................................................. 293

Integration With the Source Window ............................................................................................... 294

FSM Viewer Display Controls ......................................................................................................... 295

FSM Viewer – Transitions to Reset ................................................................................................. 298

Export the FSM Viewer Window as an Image ................................................................................ 300

Summary .......................................................................................................................................... 301

Lab 8: FSM Viewer .......................................................................................................................... 302

Module 11: Event Tracing .................................................................................. 303

Objectives ......................................................................................................................................... 304

Module Overview ............................................................................................................................. 305

Causality Traceback ......................................................................................................................... 306

Recommended Usage Flow .............................................................................................................. 307

Alternative Usage Flow .................................................................................................................... 308

Post-Simulation Causality Traceback .............................................................................................. 309

Terminology ..................................................................................................................................... 310

Causality Traceback from the GUI .................................................................................................. 311

Tracing First Sequential From the Wave Window ........................................................................... 312

Show Drivers Control Bar ................................................................................................................ 315

Tracing From the Source Window ................................................................................................... 316

Tracing From the Objects Window .................................................................................................. 318

Tracing From the Schematic Window ............................................................................................. 319

Table of Contents

ModelSim/Questa Core Advanced Topics

XI

Tracing Immediate Driver From the Wave Window ....................................................................... 321

Tracing to the Root Cause ................................................................................................................ 323

Tracing to the Root Cause of an Unknown ...................................................................................... 324

Finding All Possible Drivers ............................................................................................................ 325

Tracing from a Specific Time .......................................................................................................... 326

Viewing Causality Path Details ........................................................................................................ 327

Causality Traceback Preferences ..................................................................................................... 328

Summary .......................................................................................................................................... 329

Lab 9 : Causality Traceback ............................................................................................................. 330

Module 12: Selected Advanced Debugging Topics .......................................... 331

Objectives ......................................................................................................................................... 332

Module Overview ............................................................................................................................. 333

Debugging Issues ............................................................................................................................. 334

Checkpoint and Restore ................................................................................................................... 335

Contention and Float Checking ........................................................................................................ 336

Toggle and Stability Checking ......................................................................................................... 337

Contention, Float, and Stability Checking Script ............................................................................. 338

Example: Contention Checking ....................................................................................................... 339

Example: Float Checking ................................................................................................................. 340

Example: Stability Checking ............................................................................................................ 341

Iteration Violations ........................................................................................................................... 342

IP Integrity for compile .................................................................................................................... 344

-nodebug Command ......................................................................................................................... 345

Preoptimizing Regions of the Design ............................................................................................... 347

Table of Contents

ModelSim/Questa Core Advanced Topics

XII

Source Window: Finding Declaration .............................................................................................. 348

Source Window: Finding Where used ............................................................................................. 349

Source Window: Tracing Readers .................................................................................................... 350

Source Window: Tracing Drivers .................................................................................................... 351

Dataflow Window: Point-to-Point Tracing ...................................................................................... 353

List Window: Signal Search ............................................................................................................. 354

Wave Window: Signal Search .......................................................................................................... 355

Wave Window: Signal Grouping ..................................................................................................... 356

Saving Waveforms Between Two Cursors ...................................................................................... 357

Wave Window: Expanded Time ...................................................................................................... 358

Wave Window: Expanded Time at Active Cursor ........................................................................... 359

Wave Window: Expanded All Time ................................................................................................ 360

Wave Window: Expanded Time Deltas in the List Window ........................................................... 361

Wave Window: Events Mode .......................................................................................................... 362

Wave Window: Deltas Mode versus Events Mode .......................................................................... 363

Post-Simulation Results Analysis .................................................................................................... 364

Post-Simulation Coverage Analysis ................................................................................................. 365

Related Functional Verification Training Courses ........................................................................... 366

Summary .......................................................................................................................................... 367

Lab 10: Debugging a Design ............................................................................................................ 368