Self-Reconfigurable Bidirectional Channels in GALS NoC Routers

This thesis proposes an adaptive bandwidth allocation module (ABAM) for GALS NoCs that dynamically changes the bandwidth of channels by providing bandwidth adaptivity over bidirectional channels in multi-synchronous routers. The ABAM exploits temporal variations in bandwidth requirements by monitoring the state of the input and output buffers. The novel approach developed in this thesis is based on decreasing the frequency of the channels, resulting in a reduction of power consumption and temperature; this leads to a simplification of physical constraints and an increase in reliability, due to reduced electromigration and crosstalk.

To carry out system-level experiments, the authors developed Septimius, a highly customisable synthesizable NoCs experimentation platform. Initial experiments were performed utilising two nodes connected via a single channel using RTL simulation. This focus on a single channel's behaviour allowed the isolation and analysis of ABAM parameters and their impact on system performance, independently of other factors that could influence system performance, such as routing, arbitration, application, task mapping, etc. Proof-of-concept system-level experiments verified the agreement between hardware simulation and emulation and validated the results obtained by single-channel experiments.

The research highlights that adaptively changing the frequency of bandwidth reallocation depending on workload variations can provide better utilisation of channels in GALS-based NoC. However, the negative impact on network performance in terms of average packet latency is significant. The research also identifies several correlations between adaptive bandwidth allocation parameters and resulting effects under different traffic loads and distributions.