On-chip variation (OCV) derating for timing analysis

[robtaylor]

Summary

Apply OCV derating factors to launch vs. capture paths, matching commercial STA practice for within-die process variation.

Current State

GEM uses flat SDF delay values with no derating. Commercial tools apply different scaling factors to launch (data) and capture (clock) paths to model process variation across the die.

Proposed Approach

• Add --ocv-derate <early_factor> <late_factor> CLI flag
• For setup analysis: scale launch path delays by late factor, capture by early factor
• For hold analysis: scale launch path delays by early factor, capture by late factor
• Typical values: early=0.95, late=1.05 (5% derating)
• Future: support AOCV (path-depth-dependent derating) and SOCV (statistical OCV)

Impact

Medium — industry standard practice for signoff. Without derating, timing results are optimistic.

Effort

Medium — need to track launch/capture path separation and apply scaling.