Hardware Reference
In-Depth Information
The number of suspects reported by logic diagnosis must be limited in order
to be used for volume analysis. If the number of suspects exceeds a parameter k,
significance for certain flaws is hardly obtained and further analysis may be too
expensive. If diagnosis successfully identified the culprit, the rank describes the
position of the corresponding evidence within the ordered list.
For each fault f with e.f; T /
D
.
T
;
T
;
T
/ we have
T
C
T
>0,ifT detects
f .Otherwise,f may be undetected due to redundancy, or T must be improved to
detect f .
Even if there are no suspects with
T
>0, the possible fault sites are ranked
by
T
. This way, multiple faults on redundant lines can be pointed out. For the
special case of
T
D
0, at least a subset of DUD failures can be explained with an
unconditional stuck-at fault.
The faults with e.f; T /
D
.
T
;
T
;
T
/ and
T
>0are the suspects, and by
simple iteration over the ranking, pairs of suspects f
a
;f
b
are identified with equal
evidences e.f
a
;T/
D
e.f
b
;T/. To improve the ranking, fault distinguishing pat-
terns have to be generated (
Veneris et al.
2004
;
Bartenstein
2000
) and applied to the
DUD. To reduce the number of suspects and the region under consideration further,
diagnostic pattern generation algorithms have to be employed which exploit layout
data (
Desineni et al.
2006
).
5.5
Evaluation
5.5.1
Single Line Defects
The fault machine for a stuck-at fault f at a line a will mispredict, if the condition of
the CLF a
˚
Œcond is not active while the CLF is actually modeling the defective
behavior of line a. We split the conditions into cond
D
cond
0
_
cond
1
with
cond
0
D
a
^
cond and cond
1
D
a
^
cond.Now,a
˚
cond
0
models a conditional
stuck-at 1 fault and a
˚
Œcond
1
models a conditional stuck-at 0 fault.
The unconditional stuck-at 0 fault at line a explains all the errors introduced by
a
˚
Œcond
1
, and there is no unconditional fault which can explain more errors.
The same argument holds for the stuck-at 1 fault at line a and a
˚
Œcond
0
.Asa
consequence, assuming faults at line a will explain all the errors, and there is no line
where assumed unconditional faults could explain more errors. However, there may
be several of those lines explaining all the errors, and the ranking explained in the
section above prefers those with a minimum number of mispredictions.
In
?
(
?
) the calculus described above is applied to large industrial circuits up to 1
million of gates, and analysis of stuck-at faults was used for validating the method.
For a representative sample of stuck-at faults, the ranked lists of evidences are gen-
erated, and for all the fault candidates f with e.f;T/
D
.
T
;0;0/and a maximum
number
T
of predictions, additional distinguishing patterns are generated as far as
possible.
