Systems and methods for controlling the execution of LBIST test cycles to
allow identification of errors in bit patterns produced by the functional
logic of a device under test. In one embodiment, an LBIST controller
enables continuous execution of LBIST test cycles (including functional
and scan shift phases) prior to a test cycle in which an error arises. In
the test cycle in which the error arises, the controller allows execution
of the functional phase, but not the following scan shift phase. The
computed bit patterns captured in the scan chains are thereby retained in
the scan chains, rather than being accumulated into a single MISR
signature value. The computed bit patterns can then be retrieved from the
scan chains (e.g., via a JTAG chain) and examined to determine the exact
location of the error.