MulCh: a multi-layer channel router using one, two, and three layer partitions

Abstract

Multilayer routing is an important problem in the physical design of integrated circuits as technology evolves towards several layers of metallization. MulCh is a channel router accepting specification of an arbitrary number of routing layers. Though several other channel routers for three layers of interconnect have been proposed, the only previously reported practical implementation for an arbitrary number of layers was that of Chameleon [4]. Chameleon is based on a strategy of decomposing the multilayer problem into two and three layer problems in which one of the layers is reserved primarily for vertical wire runs and the other layer(s) for horizontal runs. In some situations, however, it is advantageous to consider also layers that allow the routing of entire nets, using both horizontal and vertical wires. Hence, MulCh incorporates layers permitting this more general type of wiring. MulCh can route channels with any number of layers and automatically chooses a good assignment of wiring strategies to the different layers. The algorithms have been devised so that MulCh is expected to always perform at least as well as Chameleon in terms of area occupied by the routing. In test cases, MulCh shows significant improvement over Chameleon in terms of channel width, net length, and number of vias.

Single-layer channel routing and placement with single-sided nets

“…Though VLSI chips generally use more than one interconnection layer, single-layer routing actually becomes more relevant as technological advances increase the number of layers on a chip. The heuristic multilayer channel router MulCh [1] obtains good results by dividing general problems into subproblems with one, two, or three layers.…”

Minimum separation for single-layer channel routing

“…For example, the heuristic multilayer channel router MulCh [5] finds good solutions to general channel routing problems by dividing them into essentially independent subproblems of one, two, or three layers. The ability to efficiently determine the minimum width of single-layer subproblems provides MulCh with a greater ability to find a good way of partitioning the original problem.…”

An Efficient Approach for Four-Layer Channel Routing in VLSI Design

“…In this example channel we can see that the net 7 starts from first column and next net 2. So, after sorting all the nets, the sorting order of the nets becomes (7,2,1,5,4,3,8,6). First we select that net N which is first in the sorted list and that is stored into another list L. Then we choose the net N s which start first after the net N ends.…”