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

ID 683082
Date 9/26/2022

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2.2.3. Optimizing Clocking Schemes

Like combinational logic, clocking schemes have a large effect on the performance and reliability of a design.

Avoid using internally generated clocks (other than PLLs) wherever possible because they can cause functional and timing problems in the design. Clocks generated with combinational logic can introduce glitches that create functional problems, and the delay inherent in combinational logic can lead to timing problems.

Tip: Specify all clock relationships in the Intel® Quartus® Prime software to allow for the best timing-driven optimizations during fitting and to allow correct timing analysis. Use clock setting assignments on any derived or internal clocks to specify their relationship to the base clock.

Use global device-wide, low-skew dedicated routing for all internally-generated clocks, instead of routing clocks on regular routing lines.

Avoid data transfers between different clocks wherever possible. If you require a data transfer between different clocks, use FIFO circuitry. You can use the clock uncertainty features in the Intel® Quartus® Prime software to compensate for the variable delays between clock domains. Consider setting a clock setup uncertainty and clock hold uncertainty value of 10% to 15% of the clock delay.

The following sections provide specific examples and recommendations for avoiding clocking scheme problems.