IBPTB-based test scheduling

During the process of wrapper scan chain balance, it is inevitable that a certain number of idle bits will appear for the inequality in length between different wrapper scan chains. In this paper, a new wrapper scan chain balance algorithm called best exchange optimization (BEO) is presented first. This algorithm aims at minimizing the number of idle bits between wrapper scan chains. Later a new test scheduling method called idle bit percentage on test bus (IBPTB)-based test scheduling (ITS) is proposed. ITS generates optimal scheduling solution according to IBPTBs of test rectangles of each IP core. The benchmark circuits in ITC´02 are selected to be the objects for test in order to demonstrate the practicability and validity of both two algorithms. Experiment on core6 of ITC´02 SOC p93791 shows that BEO can generate more balanced wrapper scan chains than those by classic best fit decreasing (BFD) heuristic algorithm. The best improvement on the length of the longest wrapper scan chain is 2.629% reduced. Experiments on both d695 and p93791 in ITC´02 show that ITS is suitable for generating better scheduling solution than classic ILP for large SOCs. For d695, only one scheduling solution can achieve lower total test time than ILP by 9.62%. For p93791, there exist several scheduling solutions like that. The best improvement on total test time can reach 26.269%.