Fully Reliable Dynamic Routing Logic for a Fault-Tolerant NoC Architecture

A fault-tolerant adaptive wormhole routing function for Networks-on-Chips (NoCs) is presented. The novelty of this routing logic is that it is capable of using runtime information on availability of links to dynamically bypass faulty channels. When faults occur, no offline reconfiguration or dropping of packets is necessary. Instead, dynamic routes are suggested on-the-fly. Routing decisions are based only on local knowledge, which allows for fast switching. Our approach does not use any costly virtual channels. As we do not prohibit cyclic dependencies, the routing function provides minimal routing from source to destination even in the presence of faults. We have implemented the architecture design using synthesizable HDL. Using simulations, we have assessed the overhead of our approach in terms of latency, power and area. On average, even with 40% of the links faulty our routing logic is capable performing correctly. Using formal verification, we have proven 100% reliability up to three faults, i.e., for any combination of three faults our routing logic remains connected, deadlock-free and livelock-free.

Deadlock Prevention with Wormhole Routing

The problem of preventing deadlocks and livelocks in computer communication networks with wormhole routing is considered. The method to prevent deadlocks is to prohibit certain turns (i.e., the use of certain pairs of connected edges) in the routing process, in such a way that eliminates all cycles in the graph. A new algorithm that constructs a minimal (irreducible) set of turns that breaks all cycles and preserves connectivity of the graph is proposed and analyzed. The algorithm is tree-free and is considerably simpler than earlier cycle-breaking algorithms. The properties of the algorithm are proven, and lower and upper bounds for minimum cardinalities of cycle-breaking connectivity preserving sets for graphs of general topology, as well as for planar graphs, are presented. In particular, the algorithm guarantees that not more than 1/3 of all turns in the network become prohibited. Experimental results are presented on the fraction of prohibited turns, the distance dilation, as well as on the message delivery times and saturation loads for the proposed algorithm in comparison with known tree-based algorithms. The proposed algorithm outperforms the tree-based algorithms in all characteristics that were considered.

Deadlock Prevention with Wormhole Routing

In this chapter, the problem of constructing minimal cycle-breaking connectivity preserving sets of turns for graphs that model regular or near regular multiprocessor systems, as a method to prevent deadlocks is investigated. Cycle-breaking provides for deadlock-free wormhole routing defined by turns prohibited at some nodes. The lower and upper bounds for minimal cardinalities of cycle-breaking connectivity preserving sets for several classes of graphs such as homogeneous meshes, p-ary n-cubes, cube-connected cycles, hexagonal and honeycomb meshes and tori, Hamiltonian graphs and others are obtained and presented along with some preliminary experimental results.