Hardware Reference
In-Depth Information
Fig. 8.10
The fault injection attributes and the fault-tolerant target system
constitute the major attributes that fully characterize a fault injection test sequence.
In practice, the fault injection test sequence is made up of a series of
experiments
;
each experiment specifies a point of the
FxAxR
space.
Figure
8.10
exemplifies these notions and further details them, in particular, to
illustrate how the attributes relate to the state space of the target system (Mealy-style
state machine). Indeed, the
A
set encompasses the primary
D
and secondary (current
state)
Y
inputs. The
A
and
F
sets fully characterize the input domain
I
and combine
together to induce errors that are the patterns meant to test the FTMs. An additional
insight shown relates to the fact that the output domain
O
extends to the primary
U
(delivery of functional service to the users) and secondary
Z
(next state) outputs.
Note also the explicit observation, as part of
R
, of the error signaling (syndrome)
provided by the FTMs when subjected to the error patterns. The figure also identifies
deficiencies in the FTMs: incapacities in handling some error situations. Such “fault-
tolerance deficiencies” are the target of the fault injection testing experiments.
8.3.1.2
Modeling the Fault Pathology
The behavior of the target system can be described by a sequence of states character-
ized by a function linking these extended attributes as ¥.
I
/
D
O
,
with
I
Df
F
;
D
;
Y
g
time
, we also consider the time dimension t . For the sake of brevity, the system
function ¥.d;y;f
I
t/ can be decomposed according to the output domain sets as
¥
z
.d;y;f
I
t/
D
z
.t
C
1/ and ¥
u
.d;y;f
I
t/
D
u
.t
C
1/.
For example, the impact of a fault vector at time t (denoted f.t/) can be per-
ceived when the fault is activated:
8
t;
9
d.t/ and=or y.t/ s
u
ch that ¥ .d; y; f
I
t/
¤
¥.d;y;f
0
I
t/
(8.1)
where f
0
.t/ designates the vector “absence of fault”.
