Retiming-based partial scan

A generally effective criterion for the selection of flip-flops in the partial scan problem for sequential circuit testability is to select flip-flops that break the cyclic structure of the circuit and reduce its sequential depth. The selection of flip-flops may also be subject to a prescribed bound on the clock period of the modified circuit (timing-driven partial scan). In this paper we propose two techniques (for non-timing-driven and timing-driven partial scan) which address the above criterion based on a transformation of sequential circuits known as retiming. For non-timing-driven partial scan, we employ retiming to rearrange the flip-flops of the circuit, so that its functionality is preserved, while the number of flip-flops that are needed to break all cycles and bound the sequential depth is significantly reduced. For timing-driven partial scan, we propose a retiming-based technique that reduces the overall area overhead required to achieve the clock period bound. Experimental results on the ISCAS'89 circuits show the benefit of our approach in both timing-driven and non-timing-driven partial scan.