Models for Delay Faults - Models in Hardware Testing - page 84

Tabl e 3. 2 TDFs detected by
functional broadside tests

Circuit # Faults # Func. det # Arb. det

S298 508 403 403

S344 552 522 522

S349 566 505 530

S382 646 488 500

S386 690 505 530

S444 764 554 568

S526 948 571 590

S641 734 575 699

S713 918 648 777

S820 1;574 1;281 1;283

S832 1;614 1;290 1;290

S1196 2;110 2;108 2;108

S1238 2;316 2;234 2;234

S1423 2;512 2;207 2;239

S1488 2;770 2;529 2;529

S1494 2;810 2;548 2;548

S5378 7;040 5;353 6;412

S35932 63;502 54;599 54;599

unreachable states, however they are restricted to state transitions that occur during
synchronization of the circuit. Additional fault coverage beyond that obtained by
functional broadside tests can be obtained using the synchronization broadside tests
( Pomeranz et al. 2009 a).

3.2.2 Pseudo-Functional Tests

Functional broadside tests require scanning in a reachable state. An alternate ap-
proach is to avoid shifting in an unreachable state. Unreachable states can be avoided
by implications learned from the sequential circuit. Several earlier works, for exam-
ple, Lin et al. ( 1998 ), Chen et al. ( 2003 ) used sequential static learning to identify
untestable stuck-at and TDF faults. These learned implications help in insuring that
the shifted in state of a broadside test is not an unreachable state. However, they
do not guarantee that a state that does not violate the learned implications is in-
deed a reachable state. For this reason tests generated using sequential learning are
called pseudo-functional tests ( Lin et al. 2005 ) . Several works have investigated
methods to generate pseudo-functional tests ( Lin et al. 2005 ; Zhang et al. 2005 ;
Syal et al. 2006 ). In Table 3.3 , the numbers of TDFs detected by pseudo-functional
broadside tests in larger ISACAS-89 benchmark circuits are given from Zhang
et al. ( 2005 ) . As expected the sets of faults detected by pseudo-functional broad-
side tests are smaller and proper subsets of the faults detected by arbitrary broadside
tests. Also pseudo-functional tests cause less switching activity during launch and
capture cycles ( Zhang et al. 2005 ). Another observation regarding the faults detected