AN 1016: Timing Closure Methodology Quick Reference Guide
3.2.1. Analyze Post-Fit Timing Reports
In timing reports, the "slack" value is the margin by which a timing requirement is met (positive slack) or not met (negative slack). Ensuring all paths have a positive slack value indicates that all timing requirements are met, meaning that all signals arrive at their destinations within the required time frame. This condition ensures that the design works correctly at the targeted clock frequency.
After the Fitter stage completes, the Timing Analyzer automatically generates a subset of all available timing reports, summarizing how closely your design adheres to each of your constraints. Timing violations display in red text for easy identification, while compliant paths display in black text. The Setup Summary report displays by default when you open the Timing Analyzer. You can also generate additional detailed reports using the Timing Analyzer Reports menu, or by entering commands at the command-line.
Analyzing the Fmax Summary Report
The Timing Analyzer's Reports > Datasheet > Report Fmax Summary command generates a report panel showing the potential maximum frequency for every clock in your design. The Fmax report column indicates your clock's fastest frequency while maintaining a positive slack. Timing analysis calculates the maximum frequency for paths where the same clock drives source and destination registers or ports, excluding paths with different clocks. However, the Fmax report does not guarantee that your design meets timing requirements for recovery, removal, setup, or hold times. You must always review the Setup, Hold, Recovery, Removal, and Min Pulse Width slack summaries to ensure your design meets timing. The Restricted Fmax column takes into account hold timing in addition to setup timing, as well as minimum pulse and minimum period restrictions. The Restricted Fmax column may also display text indicating limiting factors.
Analyzing the Report Timing Report
The Timing Analyzer's Reports > Timing Slack > Report Timing command enables you to generate customized timing reports for any path or clock domain in your design. This command allows you to specify various report generation options, including the Clocks and Targets to display, the type of analysis to run, and additional settings to configure the number of paths shown and the output report format.