Minimally buffered deflection routing with in-order delivery in a torus

Bufferless deflection routing is a serious alternative to wormhole flow control and packet switching. It is based on the principle of deflecting a flit to a non-optimal route instead of buffering it, when two flits compete for the same link. The major weakness of deflection is the exploding number of misrouted flits at high network Load, which increases the duration of flits within the network and requires to reassemble the flits at the receiver. These deflections can be reduced significantly by adding a small side buffer instead of always deflecting flits. In the presented approach, the side buffer is complemented by a restricted deflection policy that preserves the flit order: x-y-routing in an unidirectional 2D-torus ensures that collisions are impossible, as long as a flit is transported in the same direction. Only at the transition from x-to y-direction, collisions may happen and are avoided by controlled in-order deflection in x-direction. In-order delivery not only simplifies the arbitration logic, but avoids costly mechanisms for livelock-prevention and reassembly of flits at the receiver.