Functional verification of a frequency-programmable switch chip with asynchronous clock sections

An integral part of the IBM eServer z990 I/O subsystem is the self-timed interface (STI) switch chip. The STI switch is an application-specific integrated circuit (ASIC) designed to provide high I/O connectivity and high bandwidth within the system. The complexity of the functional verification of the STI switch chip is inherent in the implementation of seventeen logical clock domains and the support of six different STI interfaces with programmable frequencies. The logic within these clock domains is connected via asynchronous interfaces. This paper describes the methodology to verify the functionality of the switch chip with various STIs by introducing a combination of verification techniques. This involves random biased stimulus generation, automated result prediction checking, and the use of cycle simulation to stress the logical design. The cycle simulation required new techniques to model equivalent behavior in order to verify the correct integration of nondigital components on the chip. Advanced methods were implemented to ensure correctness of the frequency-dependent design units and functionality across the asynchronous interfaces. A single verification environment was developed, providing the flexibility to seamlessly support the different levels of design abstraction and uncover the design errors at the appropriate level.