Fault Modeling for Simulation and ATPG - Models in Hardware Testing - page 113

the above-mentioned activation conditions while [0, R max ] contains all resistances
which could theoretically result in an effect at an output.
To calculate G-FC , G-ADI information must be provided as an input. For both
E-FC and G-FC , the integral in the denominator is computed using the approxi-
mationbyweightedsumof¡. To obtain O-FC , a check is performed whether the
C-ADI is empty.

4.2.4 Experimental Results

An interval-based resistive bridging fault simulation based on the algorithms pre-
sented in this section has been implemented ( Engelke 2006b ). Table 4.1 shows
results for selected circuits from the ISCAS (Int'l Symp. on Circuits and Sys-
tems) benchmark suite. We applied 1,000 random test patterns to 10,000 ran-
domly selected non-feedback two-node bridging faults in each circuit. We derived
the density function ¡ from published data based on measurements ( Rodrıguez-
Montanes 1992 ). All four fault coverage metrics introduced here are reported for
combinational ISCAS-85 circuits and combinational cores of sequential ISCAS-89
circuits (indicated by prefix cs). The final row contains average results for all 42
ISCAS circuits.
As mentioned above, G-FC is the accurate metric, although its calculation is
complex. Hence, the usefulness of other fault coverage definitions should be judged
based on their ability to approximate G-FC at low computational cost. It turns out
that P-FC yields results which are overly pessimistic, underestimating G-FC by
more than 15% on average. On the other hand, E-FC and O-FC often provide a
tight under- and over-approximation, respectively, cs00953 being an outlier. E-FC
and O-FC define a “corridor” with an average width of some 2.5% in which G-FC is
confined. For some circuits, the accurate value of G-FC is closer to E-FC (cs13207,
cs15850), for some it is closer to O-FC (c5315, cs35932), and for some it is just in
the middle of these values (c7552, cs38584).

Tabl e 4. 1 Fault coverages for 1,000 random test patterns and 10,000 random

faults
Circuit P-FC E-FC G-FC O-FC

c5315 81.73 99.59 99.90 99.94

C7552 80.37 98.60 99.02 99.52

cs00953 82.13 92.00 97.19 98.33

cs13207 75.23 95.61 95.82 97.63

cs15850 76.46 96.37 96.69 98.04

cs35932 77.47 96.47 98.52 98.52

cs38417 79.79 95.58 97.72 99.22

cs38584 77.09 90.73 91.57 92.55

Average (42 ISCAS circuits) 80.67 95.08 96.98 97.59