Bubble sharing: Area and energy efficient adaptive routers using centralized buffers

Edge buffers along with multiple virtual channels have traditionally been used to provide deadlock freedom guarantees in on-chip networks. The problem with such schemes is their high buffer space requirement which consumes significant power and area. In this work, we propose bubble sharing flow control to provide deadlock freedom with small, shared central buffers, eliminating edge buffers, improving buffer utilization, and decreasing router buffer requirements. The key insight involves sharing of the flit-size bubbles (free buffers) among cyclic network paths via central buffers in the router, reducing the overall router buffering space requirement. This technique effectively reconciles the trade-off between high radix and buffer space, encouraging the use of low hop count, high-radix topologies, with both deterministic and adaptive routing. Comparisons show improvement in average packet latency by 31% as compared to traditional 2VC edge buffer routers with 33% reduction in area for an 8×8 generalized hypercube topology.