Integer Linear Programming Based Fault-Tolerant
Topology Synthesis for Application-Specific NoC
Zhigang Li, Jinglei Huang, Qi Xu and Song Chen
∗
Department of Electronic Sci. & Tech., University of Science and Technology of China, Hefei 230027, China
∗
Email: songch@ustc.edu.cn
Abstract—In nano era, fault tolerance has become a significant
challenge for IC designers. Even a single link failure on NoC
can halt communication between application modules, which
makes the entire chip lose efficacy. In this paper, considering link
failures, we propose an integer linear programming (ILP) based
method to generate K fault-tolerance topologies for application
specific NoCs (ASNoC). Compared with the FTTG method,
which can generate only one-link failure tolerance topologies,
the proposed mehtod show better energy efficiency and average
hops, and can scale upward to generate K (K > 1) link fault-
tolerance topologies.
I. INTRODUCTION
As an increasing number of processing elements (PEs) has
been integrated on a single chip, a variety of interconnection
schemes have been proposed, including crossbars, rings, buses,
and Network-on-Chip (NoC) [1]. The packet switching based
NoC is considered a promising solution to the interconnection
challenges of future SoC designs [2]. It is scalable and
has been widely utilized to decouple communication from
computation, thus improving performance.
However, the fast scaling in technology has caused rapid
increasing of the probability of facing faults in different NoC
components [3] while the reliability of a NoC is critical to
guarantee the reliability of communication. Even a single link
failure on NoC can halt communication between application
modules, which makes the entire chip lose efficacy.
NoC architecture consists of regular or irregular topolo-
gies. Compared to regular topologies, irregular topologies
are fitter for designing application-specific NoCs because of
low energy consumption, low area overhead, etc. [4]. There
are many works addressing the synthesis of the application-
specific NoC topologies [5]–[8]. However, these works seldom
consider fault tolerance in the NoC topologies. Especially,
the application specific NoCs have low path diversity and
could not work normally if any hardware faults occur such as
routers or links. In [9], a fault tolerant NoC architecture was
proposed with cores linked to two switches instead of one and
a dynamically reconfigured routing algorithm is used to escape
faulty switches. K.-C. Chang et al. [10] proposed a fault-
tolerant topology generation (FTTG) method for application-
specific NoC, which focuses on permanent link and router
port failures. The authors tried to add a minimum number of
extra routers and links to ensure that each router and link must
be on a cycle, which provides at least two alternative routing
paths to achieve fault-tolerance capability. The NoC topologies
are generated in two phases. In the first phase, the links
between the routers (router topology) are constructed and, in
the second phase, the links from cores to routers are built (core
mapping). However, the router topology and the core mapping
strongly depend on each other and, consequently, it is difficult
for FTTG method to effectively explore the design space
of the network topologies. Additionally, the FTTG can only
generate one-failure tolerant topologies and cannot be applied
to generating multiple-fault tolerant network topologies.
Motivated by the above argument, we propose an ILP based
method for generating multiple link-faults tolerant application-
specific topology. To generate K link-faults tolerant topologies,
we build an ILP model to simultaneously solve the router
topology generation and core mapping problem by finding
K + 1 alternative link-disjoint communication paths for each
communication flow. If there is a link failure, we can choose
another alternative path to replace the path including the link
failure. Because of K +1 alternative communication paths, the
generated topology can tolerate K link faults.
The remainder of this paper is organized as follows. Section
II formulates the K-fault-tolerant application-specific NoC
topology generation problem. In Section III, we describes the
overview of the proposed framework in III-A and present
our K-fault-tolerant topology generation methodology in III-C.
The experimental results are provided in Section IV, followed
by conclusions in Section V.
II. PRELIMINARIES &PROBL E M FORMULATION
Definition 1: (Core Communication Graph G
cc
): an undi-
rected graph G
cc
=(V
cc
,E
cc
) is defined, in which each n-
ode c
i
∈ V
cc
represents a core c
i
and each undirected edge
e
i, j
=(c
i
,c
j
) ∈ E
cc
represents the communication between the
cores c
i
and c
j
. Besides, the communication requirement for
each edge e
i, j
∈ E
cc
is given by w
i, j
. In Fig.1, we give the G
cc
of the MP3 encoder from [11].