Synchro-tokens: a deterministic GALS methodology for chip-level debug and test

This paper describes a novel deterministic globally-asynchronous locally-synchronous (GALS) methodology called "synchro-tokens". Wrappers around the synchronous blocks keep the system globally asynchronous while ensuring that each transition, although arriving at a nondeterministic time, is sensed by the synchronous block during a deterministic cycle of the local clock. This determinism facilitates debug and test methodologies, such as the use of stored-pattern testers, which are effective only when the system behavior is predictable and repeatable. Applications of synchro-tokens to GALS systems with two or more synchronous blocks and one or more asynchronous data channels are shown. Synchro-tokens supports both pipelined and unpipelined channels and a variety of clock generation methodologies. Novel schematic level designs of the wrapper components in a 180-nm technology are used to compare the performance of several different deterministic GALS design styles.