Scan-based debug methods give high observability of internal signals, however, they require halting the system to scan out responses from the circuit-under-debug (CUD). This is time consuming as many scan dumps may be required. In this paper, conventional scan chains that have non-destructive scan out capability are configured to operate as multiple MISRs during system operation. Information from the multiple MISRs is monitored periodically to identify erroneous behavior. A procedure for constructing the MISRs to maximize debug capability is described. A three step process is used to zero in on the first clock cycle in which an error is present with a small number of scan dumps. Moreover, a method for bypassing errors is described to permit debug in the presence of multiple bugs.
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