Routing L-Shaped Channels in Nonslicing-Structure Placement

The concept of L-shaped channels was first introduced in RRDO [1] to generate a feasible routing order for nonslicing-structure placement in building-block layout design. This paper presents two approaches for the L-shaped channel-routing problem. In the Manhattan approach, only horizontal and vertical wires are used. The L-shaped channel is divided into two subchannels. The vertical subchannel will be routed first, then the horizontal subchannel will be routed by a special channel router which can handle fixed terminals on 3 sides. Since the routing constraints will change during the boundary movement, several iterations may be needed to complete the routing. In the non-Manhattan approach, 45° wires are used to preserve the routing constraints when the boundary is moved in the 45° direction. With all the vertical constraints substituted by 45° constraints, the L-shaped channel-routing problem can be directly mapped into the straight-type channel-routing problem. Horizontal or vertical extension wires are used to connect terminals on an indented boundary and to separate terminals which are too close to allow the generation of 45° wires. Experimental results show that both approaches provide good solutions to the L-shaped channel-routing problem.