A cost effective system-on-a-chip (SOC) test strongly hinges on the parallel independent test of SOC cores, which can only be ensured through proper core isolation techniques. Whereas a core isolation mechanism can provide controllability and observability at the core I/O interface, its implementation may have various implications on area, functional timing, test time and data volume, and at-speed coverage on the core interface. In this paper, we provide an in-depth analysis of the soft core isolation problem by covering a wide spectrum of techniques ranging from the utilization of only functional registers to the utilization of only wrapper cells. We model the generalized problem of finding the minimum number of isolation registers, in the form of a mixture of functional registers and wrapper cells, by mapping the problem onto the maximum Boolean satisfiability problem; by utilizing the key findings in this mapping, we implement a computationally efficient heuristic for selecting a subset of core I/Os, on which wrapper cell insertion minimizes the total number of interface registers. Finally, we demonstrate the application of this heuristic, with area and performance constraints also accounted for, delivering a wide spectrum of tradeoff points for isolating a soft core.

Cost effective SOC test strongly hinges on parallel, independent test of SOC cores, which can only be ensured through proper core isolation techniques. While a core isolation mechanism can provide controllability and observability at the core I/O interface, its implementation may have various implications on area, functional timing, test time and data volume, and at-speed coverage on the core interface. This paper proposed a non-intrusive core isolation technique that is based on the utilization of existing core registers for isolating the core. The authors provide a core register partitioning algorithm that is capable of identifying the core interface registers, and of robustly isolating a core, resulting in a computationally efficient core isolation implementation that is area and performance efficient at the same time. The proposed isolation technique also ensures minimal test time increase and no at-speed coverage loss on the core interface, offering an elegant solution for soft cores, and thus enabling significant SOC test cost reductions