Synchro-tokens: eliminating nondeterminism to enable chip-level test of globally-asynchronous SoC's

Globally asynchronous locally synchronous (GALS) clocking applied to a system-on-a-chip (SoC) results in a design in which each core is a synchronous block (SB) of logic with a locally generated clock. Inter-core communication is asynchronous and controlled by wrapper logic around the cores. The nondeterministic synchronization used by most GALS architectures makes chip-level silicon debug and functional test difficult and costly. Deterministic GALS methodologies make dataflow assumptions which are only valid for a very limited set of applications. This paper describes a novel deterministic GALS methodology called "synchro-tokens" whose parameterized wrappers are flexible enough to be useful for a wide range of applications while supporting synchronous debug and test methodologies such as 1149.1 and P1500. The validation of determinism, estimation of area overhead, and analysis of performance impact are detailed.