In post-silicon debugging, only a limited number of states (flip-flops) can be traced, due to the area overhead that is introduced by trace buffers. Therefore, it is important to select the states which can restore most of the other states. There exist researches that try to heuristically select a set of flip-flops (FFs) which maximizes the number of restored FFs. Those existing works are not so robust and the cost functions used for selections do not work well in some cases. In this paper, we introduce a hardware based implementation which tries to improve selection by repeatedly swapping the flip-flops to be traced. As this is faster than software by 3-4 orders of magnitude, we can swap much more times and get consistent results even for large circuits.
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