Assess your understanding of industry-level VLSI debugging and timing closure techniques with scenario-based questions. This quiz focuses on process challenges, timing analysis, root-cause debugging, physical design issues, and solutions to common closure problems in VLSI design flows.
During post-silicon validation of a complex VLSI chip, an engineer observes setup timing violations at certain clock domains. Which approach is typically used first to identify the root cause?
Explanation: Analyzing static timing reports for critical paths helps engineers pinpoint where the largest setup margin violations occur, which is vital for root cause analysis. Changing the fabrication process is not appropriate as a first step without understanding the violation. Re-running synthesis may help after root cause is identified, but not as an initial action. Ignoring failure data risks missing genuine design issues and is not an acceptable debugging practice.
A VLSI design shows increased hold timing violations after ECO (Engineering Change Order) placement. Which factor is most likely responsible?
Explanation: Cell resizing during ECO can inadvertently increase the length and capacitance of interconnects, potentially leading to more hold violations. Power grid optimization errors primarily affect power integrity, not timing. Signal glitches from logic removal might cause functional issues but do not directly cause hold violations. Setup time miscalculation affects setup, not hold violations.
In an industry-scale VLSI design, which signoff tool report is primarily reviewed to ensure clock skew is within acceptable limits before tape-out?
Explanation: The clock tree synthesis report provides direct information about clock skew and balance across various domains, vital for timing closure before tape-out. Antenna check summaries focus on manufacturing issues during fabrication. Functional coverage relates to verification completeness, not directly to timing. Parasitic extraction sheets provide detail on wiring capacitances, but not on clock skew specifically.
An engineer discovers a failing path during timing closure that spans multiple voltage domains. What is the recommended method to robustly debug this issue?
Explanation: Reviewing level shifter placement and domain crossing techniques enables the engineer to ensure that transitions between voltage domains are properly handled, which is critical for timing integrity. Increasing chip supply voltage globally affects power and reliability, not just the domain crossing. Reducing scan chains is a test-related activity, not relevant to domain timing issues. Replacing all flip-flops with latches could introduce new timing problems and is not a standard fix.
In VLSI physical design, which scenario could result in late-stage timing violations after routing is completed?
Explanation: Excessive wirelength after routing increases resistance and capacitance (RC delay), which can degrade timing performance and cause violations. Misplaced scan-in ports might affect test access but not timing directly. Low switching activity settings in simulation affect power estimation, not physical timing. Incorrect virtual probe points are related to debug visibility but do not cause timing failures.