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

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

1.5. Deciding Which Design Blocks Should Be Design Partitions

The incremental compilation design flow requires more planning than flat compilations. For example, you might have to structure your source code or design hierarchy to ensure that logic is grouped correctly for optimization.

It is a common design practice to create modular or hierarchical designs in which you develop each design entity separately, and then instantiate them in a higher‑level entity, forming a complete design. The Intel® Quartus® Prime software does not automatically consider each design entity or instance to be a design partition for incremental compilation; instead, you must designate one or more design hierarchies below the top-level project as a design partition. Creating partitions might prevent the Compiler from performing optimizations across partition boundaries. However, this allows for separate synthesis and placement for each partition, making incremental compilation possible.

Partitions must have the same boundaries as hierarchical blocks in the design because a partition cannot be a portion of the logic within a hierarchical entity. You can merge partitions that have the same immediate parent partition to create a single partition that includes more than one hierarchical entity in the design. When you declare a partition, every hierarchical instance within that partition becomes part of the same partition. You can create new partitions for hierarchical instances within an existing partition, in which case the instances within the new partition are no longer included in the higher-level partition, as described in the following example.

In the figure below, a complete design is made up of instances A, B, C, D, E, F, and G. The shaded boxes in Representation i indicate design partitions in a “tree” representation of the hierarchy. In Representation ii, the lower-level instances are represented inside the higher-level instances, and the partitions are illustrated with different colored shading. The top‑level partition, called “Top”, automatically contains the top-level entity in the design, and contains any logic not defined as part of another partition. The design file for the top level may be just a wrapper for the hierarchical instances below it, or it may contain its own logic. In this example, partition B contains the logic in instances B, D, and E. Entities F and G were first identified as separate partitions, and then merged together to create a partition F-G. The partition for the top-level entity A, called “Top”, includes the logic in one of its lower-level instances, C, because C was not defined as part of any other partition.

Figure 6. Partitions in a Hierarchical Design

You can create partition assignments to any design instance. The instance can be defined in HDL or schematic design, or come from a third-party synthesis tool as a VQM or EDIF netlist instance.

To take advantage of incremental compilation when source files change, create separate design files for each partition. If you define two different entities as separate partitions but they are in the same design file, you cannot maintain incremental compilation because the software would have to recompile both partitions if you changed either entity in the design file. Similarly, if two partitions rely on the same lower-level entity definition, changes in that lower-level affect both partitions.

The remainder of this section provides information to help you choose which design blocks you should assign as partitions.