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Placement Steps

All PnR tools provide an option to do placement optimization. The tools usually have many settings, but you cannot just do placement optimization. You need to know the settings that effect QoR, along with those that you need learn on maybe case-to-case basis.
The single-placement command can be a complex set of several steps. They would normally be done in the sequential order:

 

  • Global placement: Coarse placement of std cells.

  • High fanout synthesis: Buffering high fanout nets.

  • Scan chain reordering: Scan chains can be reordered based on global placement to reduce wirelength and hence congestion.

  • Timing optimization:

    • Sizing of cells.

    • Vt swapping. 

    • Logical restructuring.

    • Cloning.

    • Buffering.

    • Incremental cell placement

    • Global or virtual routing estimates wirelength. This can be done almost incrementally after significant changes in placement or optimizations.

    • Incremental coarse placement for congestion removal.

    • Detail placement: Each std cell need to snap to nearest cell row with correct orientation to align with cell row. This may lead to little change in placements and hence timing.

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