Stage 1: Design Optimization - 2021.2 English

Vivado Design Suite User Guide: Design Analysis and Closure Techniques (UG906)

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2021.2 English

The Design Optimization stage is split into five steps that are executed sequentially. These steps are shown in the following diagram.

Figure 1. Design Optimization Steps

Within any given step, multiple implementation commands such as opt_design, place_design, and route_design can be run and QoR suggestions can be generated. For each step, there is a target suggestion list; if any of the generated suggestions appear on the target suggestion list, the design is reset to the required design stage for the suggestion to be successfully applied. If there are no suggestions available on the target suggestion list for a given step, the step is skipped.

The details of the Design Optimization steps are as follows.

Clean Up XDC
The design is checked for any causes that generate an implementation error and timing that is impossible to fix. If an error is picked up, the flow will exit. No suggestions are generated or applied at this stage.
Clean Up Utilization
Suggestions that reduce utilization without timing penalty are sought. In addition, some other non-utilization-based suggestions might be applied if they can be detected and fixed early in the flow.
Clean Up Clocking
The design is run to place_design to generate accurate clock skew timing numbers. If suggestions exist, the flow is reset and run through to route_design and a timing picture is generated.
Note: If there are no suggestions in the Clean Up Utilization and Clean Up Clocking stages, a special stage called First Pass is reported. This is used as a baseline reference to compare with subsequent stages. To reduce compile time, it is not generated if there are suggestions.
Clean Up Congestion
In this step, congestion suggestions are applied from post-route generated suggestions if they exist. If the design did not route, post-place generated suggestions are used.
Clean Up Timing
Individual timing paths are analyzed and suggestions applied.

At the end of stage 1 (Design Optimization), all post-route checkpoints are compared and the best run selector takes forward the best run to either stage 2 (Tool Option Exploration) or stage 3 (Last Mile Timing Closure).

To examine the modifications the IDR has made to the design, the QoR Suggestion Report shows which suggestions are GENERATED and APPLIED at each step. There are also multiple checkpoints generated which can be easily accessed from the design run directory.