Reducing Logic Delay - 2023.2 English

UltraFast Design Methodology Guide for FPGAs and SoCs (UG949)

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2023.2 English

Vivado implementation focuses on the most critical paths first, which often makes less difficult paths become critical after placement or after routing. AMD recommends identifying and improving the longest paths after synthesis or after opt_design, because it will have the biggest impact on timing and power QoR and will usually dramatically reduce the number of place and route iterations to reach timing closure.

Before placement, timing analysis uses estimated delays that correspond to ideal placement and typical clock skew. By using report_timing, report_timing_summary, or report_design_analysis, you can quickly identify the paths with too many logic levels or with high cell delays, because they usually fail timing or barely meet timing before placement. Use the methodology proposed in Identifying Timing Violations Root Cause to find the long paths which need to be improved before implementing the design.