STEP 12: STA Ownership and Real-World Flow
This step explains how Static Timing Analysis is practiced in real projects and how responsibilities are divided across teams. Understanding ownership and interaction is essential to think and work like a real STA engineer. STA is not an isolated activity; it is tightly integrated with synthesis, physical design, and signoff flows.
Role of the STA Team
The STA team is responsible for defining, validating, and signing off timing for the design. Their primary ownership is timing correctness across all modes, corners, and operating conditions.
The STA team owns the timing methodology. This includes defining clocking strategies, writing and maintaining timing constraints, setting up Multi-Mode Multi-Corner environments, and ensuring that all required timing checks are enabled and correctly interpreted.
The STA team analyzes timing reports, identifies true timing violations, distinguishes real issues from false violations, and provides clear guidance on what needs to be fixed. They are responsible for timing signoff, meaning they approve whether the design is ready from a timing perspective.
What the STA Team Owns
The STA team owns timing constraints such as clock definitions, input and output delays, false paths, multicycle paths, clock groups, and uncertainty settings.
They own timing analysis across all stages, including pre-layout, post-CTS, post-route, and signoff STA.
They own interpretation of setup, hold, recovery, removal, pulse width, and clock gating checks.
They also own correlation between different tools and stages to ensure timing consistency.
Role of the Physical Design Team
The Physical Design team is responsible for implementing fixes in the design based on STA feedback. They do not decide timing intent but implement physical and structural changes to meet timing requirements.
The PD team modifies placement, buffering, routing, cell sizing, and clock tree structures to fix timing violations identified by STA.
They ensure that timing fixes do not violate physical rules, power limits, or signal integrity requirements.
What the PD Team Fixes
The PD team fixes setup violations by optimizing logic placement, resizing cells, restructuring data paths, or improving routing.
They fix hold violations by inserting delay buffers, adjusting clock tree balance, or modifying data path delays.
They address clock skew issues by refining clock tree synthesis and balancing clock paths.
They fix routing-related timing issues such as long nets, detours, and congestion.
Interaction with Synthesis
During synthesis, STA interacts with the synthesis flow to validate timing assumptions and constraints. The STA team reviews synthesis timing reports to ensure that timing intent is met at the logical level.
Feedback from STA may result in changes to synthesis constraints, target frequency adjustments, or logic optimizations before physical implementation begins.
Interaction with CTS
During Clock Tree Synthesis, STA plays a critical role in defining clock constraints and evaluating clock quality. The STA team reviews post-CTS timing to assess clock skew, insertion delay, and clock balance.
STA feedback helps guide CTS optimization to achieve the correct trade-off between setup and hold timing.
Interaction with Routing
After routing, STA evaluates timing with extracted parasitics and signal integrity effects. The STA team identifies routing-induced timing issues and communicates them to the PD team.
The PD team then modifies routing, inserts buffers, or adjusts placement to resolve these issues.
Real-World Timing Closure Flow
In real projects, timing closure is a continuous interaction between STA and PD teams. STA analyzes, PD fixes, and STA re-analyzes. This loop continues until timing is clean across all modes and corners.
An STA engineer must understand not only timing theory but also how fixes affect physical design and downstream flows.
Goal of STA Ownership and Real-World Flow
The goal of this step is to develop a system-level understanding of STA in practice. By understanding team ownership and real-world interaction, one can think like a real STA engineer, communicate effectively with PD teams, and drive timing closure efficiently and correctly.