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

ID 683283
Date 9/24/2018
Document Table of Contents Avoid Signals That Drive Multiple Partition I/O or Connect I/O Together

Do not use the same signal to drive multiple ports of a single partition or directly connect two ports of a partition. If the same signal drives multiple ports of a partition, or if two ports of a partition are directly connected, those ports are logically equivalent. However, the software has limited information about connections made in another partition (including the top-level partition), the compilation cannot take advantage of the equivalence. This restriction usually produces sub-optimal results.

If your design has these types of connections, redefine the partition boundaries to remove the affected ports. If one signal from a higher-level partition feeds two input ports of the same partition, feed the one signal into the partition, and then make the two connections within the partition. If an output port drives an input port of the same partition, the connection can be made internally without going through any I/O ports. If an input port drives an output port directly, the connection can likely be implemented without the ports in the lower-level partition by connecting the signals in a higher-level partition.