A systematic technique for verifying critical path delays in a 300 MHz Alpha CPU design using circuit simulation

A static timing verifier is an important tool in the design of a complex high performance VLSI chip such as an Alpha CPU. A timing verifier uses a simple and pessimistic delay model to identify critical failing paths in the design, which then need to be fixed. However, the pessimistic delay model results in a large number of correct paths being identified as failing paths, possibly leading to wasted design resources. Therefore, each critical path identified by the timing verifier needs to be analyzed using a circuit simulator such as SPICE in order to confirm that it is a real failure. Setting up such a simulation is complex, especially when the critical path consists of structures appearing in a datapath of the CPU. In this paper, we present algorithms for the construction of a model for simulating the maximum delay through a critical path. This technique has been used to analyze several critical paths during the design of a 300 MHz Alpha CPU.