Generalized Fault Modeling for Logic Diagnosis - Models in Hardware Testing - page 143

culprits may be located. Second, for each of the possible fault sites, a cause-effect
simulation is performed for identifying those faults, which match the real observed
behavior ( Desineni et al. 2006 ; Amyeen et al. 2006 ). The resolution of a test set cor-
responds to the number of faults which cannot be distinguished any further ( Ve n e r i s
et al. 2004 ; Bartenstein 2000 ; Bhatti and Blanton 2006 ). The main drawback of the
cause-effect paradigms is the dependency on a fault model.

5.4.2 Fault Dictionaries vs. Adaptive Diagnosis

Cause-effect diagnosis can be speeded up, if for each fault and each failing pattern
the erroneous output is determined by simulation and then stored in a dictionary
( Pomeranz and Reddy 1992 ). Even after an effect-cause pass, the size of such a
dictionary may explode, and significant research effort has been spent for reducing
the size of fault dictionaries ( Boppana et al. 1996 ; Chess and Larrabee 1999 ; Liu
et al. 2008 ) . During debug and during diagnosis of first silicon, there exists an ef-
ficient alternative to precomputed fault dictionaries in so-called adaptive diagnosis
( Gong and Chakravarty 1995 ).
Here, we use faulty and fault free responses of the device under diagnosis (DUD)
in order to guide the automatic generation of new patterns for increasing the reso-
lution. A pattern analysis step extracts information from responses of the DUD and
accumulates them in a knowledge base. This knowledge in turn guides an automatic
test pattern generator (ATPG) to generate relevant patterns for achieving high di-
agnostic resolution. Such a diagnostic ATPG does not rely on a precomputed fault
dictionary, and significant memory savings are obtained. The loop ends, when an
acceptable diagnostic resolution is reached (Fig. 5.5 ) . The definition of the exact
abort criterion depends on the number and confidence levels of fault candidates. In
the subsequent sections we present the 'Partially Overlapping Impact couNTER'
(POINTER) approach ( Holst and Wunderlich 2009 ).

5.4.3 Pattern Analysis

In this section, we present a method to analyze the behavior of the DUD for a given
test set and a measure to quantify how well it is reflected by a certain CLF. The
SLAT paradigm will be just the special case of a perfect match for one pattern. Let
FM(f) be a fault machine, i.e. the circuit with stuck-at fault f injected. For each test
pattern t 2 T , we define the evidence

e.f; t/ D . t ; t ; t /

as tuple of natural numbers t ; t ; t 2 N (see Fig. 5.6 ) where: