Design for Testability512.3.1Ad HocApproachThead hocapproach involves using a set of design practice and modificationguidelines for testability improvement.Ad hocDFT techniques typically involveapplying good design practices learned through experience or replacing a bad designpractice with a good one. Table 2.5 lists some typicalad hoctechniques. In thissubsection, we describe test point insertion, which is one of the most widely usedad hoctechniques. A few other techniques are further described in Section 2.6.Additionalad hoctechniques can be found in [Abramovici 1994].TABLE 2.5TypicalAd hocDFT TechniquesA1Insert test pointsA2Avoid asynchronous set/reset for storage elementsA3Avoid combinational feedback loopsA4Avoid redundant logicA5Avoid asynchronous logicA6Partition a large circuit into small blocks220.127.116.11Test Point InsertionTest point insertion(TPI) is a commonly usedad hocDFT technique for improv-ing the controllability and observability of internal nodes. Testability analysis is
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