Adaptive and Deadlock-Free Tree-Based Multicast Routing for Networks-on-Chip

Abstract

This paper presents the first synthesizable network-on-chip (NoC) based on a mesh topology, which supports adaptive and deadlock-free tree-based multicast routing without virtual channels. The deadlock-free routing algorithms for unicast and multicast packets are the same. Therefore, the routing function gate-level implementation is very efficient. Multicast packets are injected to the network by sending multiple packet headers beforehand. The packet headers contain destination addresses to set up multicast trees connecting a source with multiple destination nodes. An additional locally uniform identification (ID) field is packetized together with flits belonging to the same packet. Therefore, flits of different unicast or multicast packets can be interleaved in the same queue because of the local ID-tags, which are updated and mapped dynamically to support bandwidth scalability of interconnection links. Deadlocks in tree-based multicast routing are handled using a flit-by-flit round arbitration and a fair hold-release tagging mechanism. The effectiveness of the novel mechanism has been experimented under multiple multicast conflicts scenarios, where the experimental results show that all traffic is accepted in-order and lossless in their destination nodes even if adaptive routing functions are used and the sizes of the multicast messages are very long.