Die and utilization sizing

Before placement you have to size the block. The gate netlist has a fixed total cell area; you choose how densely to pack it (utilization) and the die's aspect ratio. Utilization sets the core area, a fuller die is smaller and cheaper, and aspect sets its shape. The dashed square is the area budget.

The block starts too loose and a bit oblong: the die overflows the budget and the wires run too long.

• Fits the area budget - a bigger die costs more silicon. Pack tighter (raise utilization) to bring the core under the budget.
• Routable - too dense a die, or too skewed a shape, congests the routing. Keep utilization under the routable limit and the aspect near square.
• Timing closes - a big or oblong die stretches the longest wires; a small, square die keeps them short.

Push utilization as high as it will still route, keep the block square, then Submit design. The tightest routable square scores best.