Intel® Quartus® Prime Pro Edition User Guide: Design Optimization

ID 683641
Date 10/04/2021

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1.3.2. Critical Path Delay Reduction Trade-Offs

To meet complex timing requirements involving multiple clocks, routing resources, and area constraints, the Intel® Quartus® Prime software offers a close interaction between synthesis, floorplan editing, place-and-route, and timing analysis processes.

By default, the Intel® Quartus® Prime Fitter works to meet the timing requirements, and stops when the requirements are met. Therefore, specifying realistic constraints is crucial for timing closure.

Under-constrained designs can lead to sub-optimal results. For over-constrained designs, the Fitter might over-optimize non-critical paths at the expense of true critical paths. In addition, area and compilation time may also increase.

For designs with high resource usage, the Intel® Quartus® Prime Fitter might have trouble finding a legal placement. In such circumstances, the Fitter automatically modifies settings to try to trade off performance for area.

The Intel® Quartus® Prime Fitter offers advanced options that can help improve the design performance when you properly set constraints. Use the Timing Optimization Advisor to determine which options are best suited for the design.

In high-density FPGAs, routing accounts for a major part of critical path timing. Because of this, duplicating or retiming logic can allow the Fitter to reduce delay on critical paths. The Intel® Quartus® Prime software offers push-button netlist optimizations and physical synthesis options that can improve design performance at the expense of considerable increases of compilation time and area. Turn on only those options that help you keep reasonable compilation times and resource usage. Alternately, you can modify the HDL to manually duplicate or adjust the timing logic.