A floorplan example

Generally not every functional block would only reside on one specific layer of chip. To handle the foldable blocks introduced in the last chapter, we introduce a shadow block for each of the potentially multi-level blocks (This discussion is for stacking of two layers of chips, but can be generalized to the case of stacking more than two layers of chips). It is assumed that the area of such a block can flow from it to its shadow block and vice versa. Of course, a potentially multi-level block can also be completely placed in one layer, and if this is the case its shadow block would have an area of 0. The idea of shadow blocks is illustrated in Fig. 5.3. 

With the concept of shadow block, we are able to extend our floorplanning algorithm to handle the second formulation of 2.5-D floorplanning problem. 

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