Generalized Fault Modeling for Logic Diagnosis - Models in Hardware Testing - page 140

Dynamic pattern faults contain an additional block describing an initial condition
for a set of signals. This initial condition has to be met first, and then the signals
must change to match the values given in the REQ section. The signal values given
in the initial condition correspond to the indexed (x 1 / values in CLF notation. A
dynamic pattern fault corresponds to a CLF with one minterm in the condition. In
addition, the minterm may contain both current and indexed previous signal values.
An example of a dynamic pattern fault is described below where a transition on
signal a causes a faulty value on signal c:
DYNAMIC f
INIT f
net a 0
net b 0
g REQ f
net a 1
net b 0
PROP f
net c 1/0
g
g
In CLF, this fault corresponds to c ˚ Œ a 1 b 1 a b c. The previous values of the
signals a and b have to be 0, the current value of signal a has to be 1, signal b must
stay at 0 and signal c must be 1. If the condition of a CLF is not Boolean, it has no
representation in the pattern fault notation.
A similar notation is used in Kundu et al. ( 2006 ) which also targets test genera-
tion. The fault effect can be described as slow-to-rise or slow-to-fall signal with a
certain delay. This way, ATPG can be advised to sensitize a path of sufficient length
from the fault site to an observation point to observe the fault effect. This explicit
definition of the temporal behavior of the fault impact has no direct representation
in CLF as it cannot be directly observed in logic diagnosis.
Another very general fault modeling technique with a wide application field uses
fault tuples ( Blanton et al. 2006 ) . A single fault tuple covers either a condition in
the form of a required signal value or a fault impact in the form of a new value for
a victim signal. For example, the condition fault tuple .a;0;i/ c requires the signal
a to carry the value 0 at time i , and the excitation fault tuple .b;0;i/ e describes
a stuck-at 0 on line b at time i . The product of fault tuples combines conditions
and excitations, so that the described fault impact is only present, if all condition
fault tuples are satisfied. For instance, the product of the two tuples above models a
bridge, where signal a AND-dominates signal b. Multiple products can be combined
with the OR-operation to model more complex faults.