Intel® Quartus® Prime Standard Edition User Guide: Design Compilation

ID 683283
Date 9/24/2018
Public
Document Table of Contents

1.10.9.4. Derived Clocks and PLLs in Design Partition Scripts

If a clock in the top level is not directly connected to a pin of a lower‑level partition, the lower-level partition does not receive assignments and constraints from the top‑level pin in the design partition scripts.

This issue is of particular importance for clock pins that require timing constraints and clock group settings. Problems can occur if your design uses logic or inversion to derive a new clock from a clock input pin. Make appropriate timing assignments in your lower-level Intel® Quartus® Prime project to ensure that clocks are not unconstrained.

If the lower-level design uses the top-level project framework from the project lead, the design will have all the required information about the clock and PLL settings. Otherwise, if you use a PLL in your top-level design and connect it to lower-level partitions, the lower-level partitions do not have information about the multiplication or phase shift factors in the PLL. Make appropriate timing assignments in your lower‑level Intel® Quartus® Prime project to ensure that clocks are not unconstrained or constrained with the incorrect frequency. Alternatively, you can manually duplicate the top‑level derived clock logic or PLL in the lower-level design file to ensure that you have the correct multiplication or phase-shift factors, compensation delays and other PLL parameters for complete and accurate timing analysis. Create a design partition for the rest of the lower-level design logic for export to the top level. When the lower‑level design is complete, export only the partition that contains the relevant logic.