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To reduce test application time, a proper scheduling is necessary for the cores.
Even if we assume the availability of multiple I/O channels from the
Automated
Test Equipment
(ATE), system pins may be associated with only a few cores,
primarily dedicated for input-output operations. Test patterns are to be routed
from such an input core to an output core. Thus, even if multiple I/O cores
are available, test parallelism may be restricted by the availability of routing
resources through the NoC.
As a result, NoC test scheduling has become a major research area. The non-
preemptive version of the problem is
NP-hard
[1]. The fully preemptive version
is solvable optimally in
O
(
n
3
) time [1],
n
being the number of cores. The prob-
lem can be solved as an instance of job-shop problem. The test session for the
sequential and BIST based core, in practice, may be nonpreemptive [2]. There-
fore, all cores in a NoC need not be preemptive. Purely combinational cores may
be taken as preemptive, sequential or BIST based core testing is not preemp-
tive. Preemption also depends on type of fault-model assumed. In particular, the
assumption does not hold for transition and linked faults. Ideally, a NoC will
contain cores such that, only a subset of them support preemptive testing. Thus,
the overall scheduling problem remains NP-hard. A judicious mix of sequences
testing preemptive and non-preemptive cores can have better flexibility in utiliz-
ing test times which may otherwise remain idle, due to resource conflicts. This
has motivated us to formulate a
Particle Swarm Optimization
(PSO) problem
to identify test schedule for NoCs having both types of core.
The rest of the paper is organized as follows. Section 2 presents the problem
definition along with the test time computation for individual cors. Section 3
presents a survey of related works on test scheduling. Section 4 and 5 enumerates
the PSO formulation. Result has been discussed in Section 6. Section 7 draws
conclusion.
2 Problem Definition
The input to the test scheduling problem consists of the following.
-Aset
C
=
of
N
c
cores in the NoC.
- Each core
C
i
has a test set
T
i
associated with it. The test may be preemptive
or non-preemptive in nature. A non-preemptive test set has to be applied
to the core as a single group. On the otherhand, a preemptive test can be
divided into multiple test sessions for a single core.
-Asetofpairs
P
of cores marked as input-output pairs. The overall test
scheduling problem is to identify the schedule to test all cores in the system.
{
C
i
,
1
≤
i
≤
N
c
}
To test a core, a test wrapper interfaces between the core and NoC environ-
ment. Test wrappers convert core scan-chains into wrapper scan-chains (each of
almost equal length). In this work, we have used test wrapper design algorithm
proposed in [4]. A mesh based NoC implementation of ITC benchmark
d695
[5]
has been shown in Fig. 1. It has two number of I/O pairs indicated by the in-
coming and outgoing arrows. A channel of an
Automatic Test Equipment
(ATE)
