# PCCNoC: Packet Connected Circuit as Network on Chip for High Throughput and Low Latency SoCs
## 2 Related Work
FastPass can transfer packets via the pre-defined non-overlapping lanes to guarantee that the packet is not blocked by congestion or deadlock. Extra lanes are need for routers, which increases the design complexity of SoC. FastTrackNoC [23] presents a method of bypassing the VC switch traversal (ST) stage to reduce packet latency. It adds a fast-track path to a 2D mesh router between the head of a single input virtual channel (VC) buffer and its most used opposite output to reduce router processing time. CS NoCs mainly use the fully customized network connections method [24; 25; 26; 27; 28; 29]. Fully customized network connections are based on static communication task graphs. However, as the flexibility of such architectures is limited to a specific application, they lack flexibility in modern many-core architectures, where multiple tasks of applications are scheduled to run concurrently. As a result, they may not support applications such as H.264 [30] which requirement dynamic communication setups. Many hybrid NoCs have been proposed in recent research. The connection setup of hybrid switch networks can be implemented by a packet configuration [31; 32; 33; 34] or by a master-controlled dedicated network configuration [35; 36; 37; 38]. In [32], a technique called Hybrid Circuit Switching \"HCS\" is presented. It consists of a network setup which handles the construction and reconfiguration of circuits and then stores the switch configuration for active circuits, along with a data network for packet transferring which intermingles circuit-switched flits with packet-switched flits. The packet does not wait for an acknowledgment that a circuit has been successfully constructed. If there are no unused circuit planes, incoming circuit-switched (CS) flits are tagged as packet-switched flits and remain packet-switched until their destination. QoS cannot be guaranteed, as the router can change the packet type dynamically. In [34], a TDM (time division multiplexing) circuit-switched part for transferring Guaranteed Service (GS) packets and a packet-switched part for transferring best effort (BE) packets were proposed. The packet switched network utilizes the unreserved resources to increase resource utilization. The problem is that the setup latency is not guaranteed, because of the unpredictable contention of best-effort packets. In the CirKet switching mechanism [35], messages are divided into two different priority classes: high priority (HP) messages and low priority (LP) messages. HP packets have a higher priority as compared to LP packets in obtaining network resources. HP uses pseudo-circuit switching that does not share network resources with other communications. LP changes crossbar configuration to establish new link communication. This requires external router calculation time, as LP and HP can be transferred simultaneously. PCSAT_NET [37] is composed of a configuration network (Cfg_net), a status network (Stat_net), and a data network (Data_net). It uses a dedicated configuration network for communication setup and a specific state network for state information transferring. It is able to solve the problem of long path locking time, however, the trade-off in terms of increased silicon cost and time certainty has to be considered.