Quartus® Prime Standard Edition User Guide: Design Compilation

ID 683283
Date 10/22/2021
Document Table of Contents Perform Timing Budgeting if Required

If you optimize partitions independently and integrate them to the top-level design, or compile with empty partitions, any unregistered paths that cross between partitions are not optimized as entire paths. In these cases, the Quartus® Prime software has no information about the placement of the logic that connects to the I/O ports. If the logic in one partition is placed far away from logic in another partition, the routing delay between the logic can lead to problems in meeting timing requirements. You can reduce this effect by ensuring that input and output ports of the partitions are registered whenever possible. Additionally, using the same top-level project framework helps to avoid this problem by providing the software with full information about other design partitions in the top-level design.

To ensure that the software correctly optimizes the input and output logic in any independent partitions, you might be required to perform some manual timing budgeting. For each unregistered timing path that crosses between partitions, make timing assignments on the corresponding I/O path in each partition to constrain both ends of the path to the budgeted timing delay. Assigning a timing budget for each part of the connection ensures that the software optimizes the paths appropriately.

When performing manual timing budgeting in a partition for I/O ports that become internal partition connections in a top-level design, you can assign location and timing constraints to the virtual pin that represents each connection to further improve the quality of the timing budget.

Note: If you use design partition scripts, the Quartus® Prime software can write I/O timing budget constraints automatically for virtual pins.