Vivado error: Timing not met (negative WNS) - what to do?
Vivado
Fig: Critical path timing violation — setup margin insufficient, WNS is negative
Analyze timing violations and optimization: pipelining, constraints, logic simplification, resource allocation.
A negative WNS (Worst Negative Slack) means data does not arrive stably within the setup window before the capturing clock edge. Common causes: too many combinational logic stages, routing congestion, clock skew, and unreasonable constraints.
Fig: Data arrives too late on the critical path, leaving negative setup slack (WNS < 0)
To fix it, compress the critical path first: insert pipeline registers to split long paths, refine physical constraints and routing strategy, use set_multicycle_path for multi-cycle paths and set_false_path for false paths, and simplify logic or rebalance resources to reduce single-stage delay.