A BIST scheme for RTL controller-data paths based on symbolic testability analysis

This paper introduces a novel scheme for testing register-transfer level controller/data paths using built-in self-test (BIST). The scheme uses the controller netlist and the data path of a circuit to extract a test control/data flow (TCDF) which consists of operations mapped to modules in the circuit and variables mapped to registers. This TCDF is used to derive a set of symbolic justification and propagation paths (known as test environment) to test some of the operations and variables present in it. If it becomes difficult to generate such test environments with the derived TCDFs, a few test multiplexers are added at suitable points in the circuit to increase its controllability and observability. This test environment can then be used to exercise a module or register in the circuit with pseudorandom pattern generators which are placed only at the primary inputs of the circuit. The test responses can be analyzed with signature analyzers which are only placed at the primary outputs of the circuit. Every module in the module library is made random-pattern testable, whenever possible, using gate-level testability insertion techniques. Finally a BIST controller is synthesized to provide the necessary control signals to form the different test environments during testing, and a BIST architecture is superimposed an the circuit. Experimental results on a number of industrial and university benchmarks show that high fault coverage (>99%) can be obtained with our scheme in a small number of test cycles at an average area (delay) overhead of only 6.4% (2.5 %).