Reconfigurable Scan Networks: Modeling, Verification, and Optimal Pattern Generation

Efficient access to on-chip instrumentation is a key requirement for post-silicon validation, test, debug, bringup, and diagnosis. Reconfigurable scan networks, as proposed by, for example, IEEE Std 1687-2014 and IEEE Std 1149.1-2013, emerge as an effective and affordable means to cope with the increasing complexity of on-chip infrastructure. Reconfigurable scan networks are often hierarchical and may have complex structural and functional dependencies. Common approaches for scan verification based on static structural analysis and functional simulation are not sufficient to ensure correct operation of these types of architectures. To access an instrument in a reconfigurable scan network, a scan-in bit sequence must be generated according to the current state and structure of the network. Due to sequential and combinational dependencies, the access pattern generation process (pattern retargeting) poses a complex decision and optimization problem. This article presents the first generalized formal model that considers structural and functional dependencies of reconfigurable scan networks and is directly applicable to 1687-2014-based and 1149.1-2013-based scan architectures. This model enables efficient formal verification of complex scan networks, as well as automatic generation of access patterns. The proposed pattern generation method supports concurrent access to multiple target scan registers (access merging) and generates short scan-in sequences.