Buffer Placement on a Setup Path

Normally setup is fixed by sizing cells; buffers are mainly for fanout. If a buffer must be inserted, place it near the capture flop.

Paths near the launch flop may share or originate from that flop, so a buffer there could affect many other paths - improving some and degrading others. Insert near the launch flop only if all those paths are violating and the change improves overall slack.

KEY Insert near the capture flop to avoid disturbing other paths sharing the launch flop.

Setup Violation Surviving Placement

A setup violation after placement is usually not alarming unless it comes from a genuinely bad placement. Check the macro and module placement - for example, a module being split across several clusters can be fixed with placement guides or bounds.

Give the tool the right constraints at placement, re-run with high timing effort, and let CTS and routing optimization take further passes - each stage improves things. Large slacks (even -500ps over thousands of paths) are aggressively closed later by the STA team using upsizing, DRV fixes and LVT swaps.

Remember the place-stage routing and timing engines are not sign-off quality and cannot match tools like PrimeTime or Tempus.

KEY Don't panic - check placement quality, raise effort, and let CTS/routing/STA close it later.

Placement Optimization in SoCE and Astro

• Pre-place optimization.
• In-place optimization.
• Post-place optimization.
• Incremental optimization.
• Timing-driven optimization.
• Congestion-driven optimization.