Optimal test access architectures for system-on-a-chip

Test access is a major problem for core-based system-on-a-chip (SOC) designs. Since embedded cores in an SOC are not directly accessible via chip inputs and outputs, special access mechanisms are required to test them at the system level. An efficient test access architecture should also reduce test cost by minimizing test application time. We address several issues related to the design of optimal test access architectures that minimize testing time., including the assignment of cores to test buses, distribution of test data width between multiple test buses, and analysis of test data width required to satisfy an upper bound on the testing time. Even though the decision versions of all these problems are shown to be NP-complete, they can be solved exactly for practical instances using integer linear programming (ILP). As a case study, the ILP models for two hypothetical but nontrivial systems are solved using a public-domain ILP software package. © 2001 ACM.