Generalized Fault Modeling for Logic Diagnosis - Models in Hardware Testing - page 139

5.3.1.1 Other General Fault Models

The idea of generalizing fault modeling to describe complex defects is not new.
However, the main motivation of the previous works was more related to test gen-
eration than to diagnosis. For efficient test generation, the initial values of internal
signals, the preconditions and the fault effects have to be given explicitly in a formal
way. Therefore, these notations are more restrictive in their formulation of condi-
tions than CLFs. We will take a quick look at three modeling approaches and discuss
their relation to the CLF calculus.
Pattern faults ( Keller 1996 ) distinguish between static and dynamic faults. Static
faults have a condition in the form of a set of required signal values. If the condition
is met, the fault is active and its impact is described as a set of value changes on
internal signals. The following example shows the description of a static OR-bridge:

STATIC f
REQ f
net a 1
PROP f
net b 0/1

g

g

Signal b changes from 0 to 1 if the aggressor signal a is 1. Two conditions have
to be met in order to detect this fault. Signal a has to be 1, and signal b has to be 0.
In CLF notation, this fault is equivalent to b ˚ Œa b.
In general, a pattern fault may require multiple signals to carry a specific value.
This corresponds to a conjunction of these signals in the condition of a CLF. If
the condition of CLF is a Boolean formula with only one minterm, the fault can
be expressed in the pattern fault model. The fault a ˚ Œb c for instance can be ex-
pressed as:

STATIC f
REQ f
net b 1
net c 0
PROP f
net a 0/1
net a 1/0

g

g

In contrast to the CLF calculus, the propagation description has two terms.