Towards an automatic generation of diagnostic in-field SBST for processor components

This paper deals with a diagnostic software-based self-test program for multiplexer based components in a processor. These are in particular the read ports of a multi-ported register file and the bypass structures of an instruction pipeline. Based on the detailed analysis of both multiplexer structures, first a manually coded diagnostic test program is presented. This test program can detect all single and multiple stuck-at data- and address faults in a multiplexer structure. But it does not fully cover the control-logic of the bypass. By further refinements a 100% fault coverage for single stuck-at faults, including the control logic, is finally obtained. Based on these results, an ATPG-assisted method for the generation of such a diagnostic test program is described for arbitrary processor components. This method is finally applied to the multiplexer structures for which the manually coded test program is available. The test length and test coverage of the generated test program and of the hand-coded test program are compared.