RSBST: an Accelerated Automated Software-Based Self-Test Synthesis for Processor Testing

Software-based test (SBST) techniques are increasingly being used for testing of modern processors because of the ease of synthesis using evolutionary approaches, coverage for difficult to test faults, non-intrusive nature, low hardware overhead, etc. However, the test synthesis time required by SBST is high. In this paper, an advanced SBST technique, termed as Rapid SBST (RSBST) is proposed that reduces the overall test synthesis time by reusing the simulation responses of existing test programs of identical observability. The test codes, developed using the evolutionary process, that produce similar fault simulation results are reused for the fault evaluation. We exploit this reusability to enhance the speed of the test synthesis process. The efficacy of the proposed scheme is demonstrated on a 32-bit MIPS processor and on a minimal configuration of 7-stage SPARC V8 Leon3 soft processor. The traditional SBST synthesis requires 122 hours for the MIPS processor and 142 hours for the Leon3 processor to develop test program sets that cover 93.9% and 92.9% of the behavioral-level faults of these processors, respectively. An existing enhanced greedy-cover method, that also detects the hard-to-test faults, improves the coverage towards 96.3% for the MIPS processor and 95.8% for the Leon3 processor, but this slower test development consumes 168 hours and 172 hours, respectively. In the proposed RSBST scheme, the synthesized test codes achieve an adequate fault coverage of 96.1% for the MIPS processor and 95.5% for the Leon3 processor. This accelerated test pattern generation takes 90 hours and 98 hours for these two processors. So it may be concluded that the proposed RSBST technique speeds up the traditional SBST synthesis by a factor of 1.35 while maintaining the fault coverage above 95.5%. To validate the test quality evaluation using behavioral fault models, a strong correlation (94.8%) between the behavioral faults and gate-level faults of MIPS processor is demonstrated and verified for the proposed RSBST scheme. Also, the simulation responses of the test programs synthesized by RSBST scheme consumes only 14.25% of storage space when compared with the storage consumption of the actual simulation used by the existing test code generation methods.