solution to these limitations lies in adopting the flexible and novel
partitioning strategy for hierarchically designs outlined in this paper.
The attribute of the partition will be defined as COVER cell. Placement
and routing of partitions is reclosed in ECO (Engineering Change Order)
mode without any change in top-level placement. The proposed closure
technique is subdivided into top-level (placement frozen) and
block-level (ECO mode) implementation.
Reconsider Case 1
block-level implementation. Congestion is seen over the bottom side of
partition A, when merged at the top. In order to resolve this
congestion, the designer has to manipulate partition A to free some
resources in terms of area for top. As discussed, shrinking the size of
the partition will reset the entire block closure activities and need
extra resources for re-closure. The proposed approach is based upon
virtual shrinking of the block size. This means getting area from the
blocks and allocating the same space for top in congested regions
without changing actual block width/height and without major changes in
block-level placement and routing. This can be done by generating empty
area in the block, using placement and routing blockages where no
standard cells are placed and no signals are routed.
Assume the floorplan for partition A is similar to that shown in figure 4.
Figure 4: Case study floorplan for partition A (before and after implementation)
to pin placement along the bottom side of partition A, there is little
to do there. In order to get some area from partition A, the only option
left is on the top side of the partition where memories and some logic
cell are placed. To get area from top, establish a placement and routing
blockage at the top side in partition A, and move the memories out from
these blockages (shifting down as shown in figure 4). Do the placement
and routing in ECO mode so that only the placement and routing of the
standard cells that are in the blockage region get re-placed and
re-routed rather than performing complete closure from scratch. This
will generate the white space at top side, which can be viewed as
virtually shrinking the block from Y to Y’= Y - delta Y from the top