Integrated LFSR Reseeding, Test-Access Optimization, and Test Scheduling for Core-Based System-on-Chip

We present a system-on-chip (SOC) testing approach that integrates test data compression, test-access mechanism/test wrapper design, and test scheduling. An efficient linear feedback shift register (LFSR) reseeding technique is used as the compression engine. All cores on the SOC share a single on-chip LFSR. At any clock cycle, one or more cores can simultaneously receive data from the LFSR. Seeds for the LFSR are computed from the care bits for the test cubes for multiple cores. We also propose a scan-slice-based scheduling algorithm that attempts to maximize the number of care bits the LFSR can produce at each clock cycle, such that the overall test application time (TAT) is minimized. This scheduling method is static in nature because it requires predetermined test cubes. We also present a dynamic scheduling method that performs test compression during test generation. Experimental results for International Symposium on Circuits and Systems and International Workshop on Logic and Synthesis benchmark circuits, as well as industrial circuits, show that optimum TAT, which is determined by the largest core, can often be achieved by the static method. If structural information is available for the cores, the dynamic method is more flexible, particularly since the performance of the static compression method depends on the nature of the predetermined test cubes.