Routing With Constraints for Post-Grid Clock Distribution in Microprocessors

Microprocessors typically employ a global grid followed by block-level buffered trees for clock distribution. The trees are connected to the grid by routing wires along reserved tracks. The routing of these clock wires, which present load to the grid, is constrained by delay/slope requirements at inputs of the block-level trees. This leads to a capacitance minimization problem during multiterminal routing, where routes use the reserved tracks and obey the constraints. This paper presents an algorithm that addresses the problem, improving wirelength by 14% over a competitive approach. The algorithm is employed for post-grid clock distribution in a 45 nm technology microprocessor.