A Guide to SDC-based Timing Intent Verification with Questa One

As semiconductor designs continue to grow in complexity and timing margins become increasingly constrained, achieving predictable timing closure has evolved from a best practice into a critical requirement for first-pass silicon success. At the heart of this process lies the timing constraint file, i.e., the SDC (Synopsys Design Constraints), which defines the intended timing behavior of the design—including clocks, timing paths, and exception conditions. Despite its significance, SDC verifica­tion is often approached as a manual task or checklist item rather than a structured and integrated design flow step.

The risks of inadequate constraint verification are well understood. Under-constraining the design may obscure timing violations that only surface during silicon validation. On the other hand, over-constraining can lead to increased area and power consumption due to unnecessary buffering, logic replication, etc. As design schedules shorten and functional modes that a chip has to operate in increase, the need for a more automated and thorough approach to constraint verification is becoming crucial.

Questa™ One Sim addresses this challenge by providing an automated and compre­hensive solution for SDC verification. It integrates static structural checks and simulation-based verification to evaluate constraint correctness, completeness, and consistency. The tool detects common issues such as invalid or unused false and multicycle path declarations, undefined or misapplied clock definitions, and other inconsistencies.

A key advantage of Questa One Sim is its ability to measure constraint coverage, enabling teams to quantify which aspects of the SDC have been explicitly validated. It integrates seamlessly into existing simulation environments to correlate exception paths with actual design activity, thereby ensuring that constraints are not only syntactically correct but also behaviorally aligned with the underlying RTL.

By enabling higher levels of automation and visibility, Questa One Sim with its faster engines, empowers engineering teams to operate more efficiently and become faster engineers, allowing designers to focus on creation and refinement rather than late-stage debugging. This leads to faster engineers and, by comprehensively verifying the constraints, synthesis, place-and-route, and static timing analysis (STA) tools. Thus, Questa One Sim accelerates convergence, improves the reliability of signoff, and transforms SDC verification from a reactive, post-hoc activity into a proactive design step that is essential for modern SoC design.