Systematic software-based self-test for pipelined processors

Software-based self-test (SBST) has recently emerged as an effective methodology for the manufacturing test of processors and other components in systems-on-chip (SoCs). By moving test related functions from external resources to the SoC's interior, in the form of test programs that the on-chip processor executes, SBST eliminates the need for high-cost testers, and enables high-quality at-speed testing. Thus far, SBST approaches have focused almost exclusively on the functional (directly programmer visible) components of the processor. In this paper, we analyze the challenges involved in testing an important component of modern processors, namely, the pipelining logic, and propose a systematic SBST methodology to address them. We first demonstrate that SBST programs that only target the functional components of the processor are insufficient to test the pipeline logic, resulting in a significant toss of fault coverage. We further identify the testability hotspots in the pipeline logic. Finally, we develop a systematic SBST methodology that enhances existing SBST programs to comprehensively test the pipeline logic. The proposed methodology is complementary to previous SBST techniques that target functional components (their results can form the input to our methodology), and can reuse the test development effort behind existing SBST programs. We applied the methodology to two complex, fully pipelined processors. Results show that our methodology provides fault coverage improvements of up to 15% (12% on average) for the entire processor, and fault coverage improvements of 22% for the pipeline logic, compared to a conventional SBST approach.