Apec: Improved Acknowledgement Prioritization Through Erasure Coding In Bufferless Nocs

Bufferless NoCs have been proposed as they come with a decreased silicon area footprint and a reduced power consumption, when compared to buffered NoCs. However, while known for their inherent simplicity, they suffer from early saturation and depend on additional measures to ensure reliable packet delivery, such as control protocols based on ACKs or NACKs. In this paper, we propose APEC, a novel concept for bufferless NoCs that allows to prioritize ACKs and NACKs over single payload flits of colliding packets by discarding the latter. Lightweight heuristic erasure codes are used to compensate for discarded payload flits. By trading off the erasure code overhead for packet retransmissions, a more efficient network operation is achieved. For ACK-based networks, APEC saturates at 2.1x and 2.875x higher generation rates than a conventional ACK-based bufferless NoC for packets between 5 and 17 flits. For NACK-based networks, APEC does not require concepts such as deflection routing or circuit-switched overlay NACK-networks, as prior work does. Therefore, it can simplify the network implementation compared to prior work while achieving similar performance.