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Debugging-Driven Content

Written by signoff engineers — GLS taught as a debugging discipline, not a tool-command list. You learn to root-cause the X, reset, and timing failures the netlist exposes.

Interview-Ready Depth

Topics mirror what GLS and signoff interviews actually test — SDF annotation, X-propagation, setup/hold debug, CDC behaviour, and low-power sim.

Working-Example Driven

One progressive project — a D flip-flop grown into a mini-SoC — with RTL, netlist, SDF, testbench, expected log, and a debug walkthrough behind every concept.

Gate Level Simulation Complete Curriculum

Your Learning Roadmap

16 chapters · 87 tutorials — from your first netlist to a mini-SoC signoff flow.

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Chapter 0
GLS Foundations
0.1Why Gate-Level Simulation Exists0.2What GLS Catches That Nothing Else Does0.3Where GLS Sits in the RTL-to-Signoff Flow0.4Zero-Delay vs Unit-Delay vs Full-Timing GLS0.5A Mental Model for Reading Gate-Level Sims
Chapter 1
RTL vs Gate-Level Simulation
1.1How Netlist Behaviour Diverges from RTL1.2What Synthesis Changes — and Why It Matters1.3Initial Blocks, Force & Constructs That Vanish1.4Four-State vs Two-State Simulation1.5Working Example: A D Flip-Flop from RTL to Gates
Chapter 2
Netlists & Standard-Cell Libraries
2.1Anatomy of a Synthesized Netlist2.2Inside a Standard-Cell Library (.lib)2.3Cell Simulation Models & UDPs2.4specify Blocks & Timing Arcs2.5Sequential Cell Models: Notifiers & Timing Checks2.6Working Example: Reading a Counter Netlist
Chapter 3
Timing Basics for GLS
3.1Delay Types: Distributed, Lumped & Pin-to-Pin3.2Setup, Hold & Timing-Check Fundamentals3.3Interconnect Delay & the Post-Layout Picture3.4Timing Corners: Which Corner to Simulate & Why3.5Pulse Rejection & Glitch Behaviour
Chapter 4
SDF Annotation
4.1What SDF Is and What It Carries4.2Anatomy of an SDF File4.3The SDF Back-Annotation Flow4.4MIN:TYP:MAX and Delay Selection4.5Debugging Failed & Partial SDF Annotation4.6Working Example: Annotating the Counter with SDF
Chapter 5
GLS Testbench Adaptation
5.1Why an RTL Testbench Breaks on the Netlist5.2Hierarchical References & Bind After Synthesis5.3Timing-Aware Stimulus & Clock Generation5.4Writing GLS-Friendly Checkers & Strobes5.5Working Example: Adapting an FSM Testbench
Chapter 6
X-Propagation
6.1Where X Comes From at the Gate Level6.2X-Pessimism vs X-Optimism6.3How X Flows Through Muxes, Flops & Latches6.4Why RTL Hides Bugs the Netlist Exposes6.5Controlling X-Propagation (Xprop Modes)6.6Working Example: Root-Causing an X in the FSM
Chapter 7
Reset & Initialization Debug
7.1Reset Behaviour at the Gate Level7.2Uninitialised Flops & the Startup Problem7.3Asynchronous Reset Assertion & Release7.4Reset Sequencing Across a Design7.5Working Example: Debugging a Stuck Reset
Chapter 8
Timing-Violation Debug
8.1Reading Setup/Hold Violation Messages8.2Root-Causing a Setup Violation8.3Root-Causing a Hold Violation8.4Real Violations vs Simulation Artifacts8.5Timing Checks, Notifiers & X-Injection8.6Working Example: A Clock-Gated Block Violation
Chapter 9
CDC & Asynchronous Behaviour in GLS
9.1What GLS Reveals About Clock-Domain Crossings9.2Metastability & Why Simulators Can't Model It9.3Synchronisers Under Real Delays9.4Asynchronous FIFO Behaviour in GLS9.5Working Example: A CDC Glitch Only GLS Caught
Chapter 10
Low-Power GLS
10.1Power Intent & UPF for Simulation10.2Power-Aware Gate-Level Simulation10.3Isolation & Level-Shifter Cells in Sim10.4Retention Flops & State Across Power-Down10.5Power Switching, Corruption & X-Injection10.6Working Example: A Power-Gated Clock-Gated Block
Chapter 11
Scan / DFT Interaction
11.1Where DFT and GLS Intersect11.2Scan Chains in the Netlist11.3Simulating Shift & Capture11.4ATPG Pattern GLS & Mismatch Debug11.5Working Example: Scan Reset & X Issues
Chapter 12
GLS Debug Methodology
12.1A Repeatable GLS Debug Mindset12.2Triaging the First Point of Divergence12.3Waveform Debugging at the Gate Level12.4Force, Deposit & Bisecting a Failure12.5RTL-vs-GLS Comparison & Mismatch Isolation12.6Common GLS Mistakes & How to Avoid Them
Chapter 13
Simulation Performance & Regression Strategy
13.1Why GLS Is Slow — and What to Do About It13.2Speeding Up Gate-Level Runs13.3Choosing What to Run in GLS13.4GLS in the Regression & Signoff Pipeline13.5Automating GLS Triage & Reporting
Chapter 14
Industry Case Studies
14.1DFF: From RTL to a Clean GLS Run14.2Counter: Full-Timing GLS with SDF14.3FSM: X-Cleanup & Reset Signoff14.4UART / Timer Peripheral GLS14.5AXI-Lite Peripheral GLS14.6Mini-SoC GLS Signoff Flow
Chapter 15
Interview & Signoff Review Preparation
15.1Top GLS Interview Questions15.2Scenario-Based GLS Questions15.3GLS Debug Drills15.4GLS Signoff Review Checklist15.5GLS Readiness Self-Assessment