Design planning for large SoC implemention at 40nm - Part 3

Bhupesh Dasila
EDN (August 9, 2013)

[Part 1 explores the process technology to learn its capabilities and limitations, including evaluating the technology libraries, determining the implementation tools and flows, and capturing the SoC requirements.

Part 2 covers comprehensive planning for complex designs at lower geometry.]

Floorplanning and PnR

A thorough exercise during physical architecture is the foundation for an efficient floorplan. It helps in reducing the overall turnaround time of the physical design phase. The broader prospective of the floorplan should be performed during the physical architecture phase, and the actual floorplaning phase should address the finer details of the floorplan, which impacts the physical design’s QoR.

Floorplanning guidelines

The seed for a floorplan primarily comes from physical architecture, die size-power estimation exercise and the technology. When creating a floorplan, it’s important to consider some basic characteristics of the process technology. The designer should have explored the technology enough in the context of metal stack and metal configuration. Also the designer should have gained ample experience about the availability of vertical and horizontal routing resources and their requirements for the design as per the physical architecture.

At any level, creating “non-preferred” routing (i.e. not using the preferred routing direction for that level) is not recommended. In the case of a channel-based floorplan, when placing blocks, four-way intersections in top-level channels should be avoided; “T” intersections create much less congestion. This consideration can be critical in leaving adequate space for routing channels, especially if there is not much opportunity for over-the-cell routing. Using fly lines can help determine optimal placement and orientation, but when the fly lines are numerous enough to “paint the area” between blocks, designers must rely on their best judgment for block placement, and later evaluate the results for possible modification.

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