Enhanced switching activity balancing encoding schemes for uniform temperature distribution in on-chip buses

Abstract

With technology scaling, power dissipation and localized heating in global and semi-global bus wires are becoming increasingly important. One way to mitigate these effects is to ensure uniform switching of bus wires. This prevents the unusual heating of some wires causing gradients, leading to various undesired effects. Thermal Spreading has shown to be a successful approach to bus temperature minimization. The idea at the basis of this technique is that of periodically permuting the routing of input bitstreams to the various bus lines, with the objective of temporally and spatially distributing the number of transitions over the entire bus. This prevents high switching activities from pertaining only to a few lines which causes an unnatural increase in temperature. In this paper, we propose new encoding schemes which improve the capability of the Thermal Spreading approach of balancing switching activities over the bus wires. The solutions we introduce are adaptive and dynamic in nature, as they select the bitstream and it's appropriate bus line based on online monitoring of actual bus traffic. This is possible thanks to some ad-hoc hardware unit running in parallel at the transmitting and receiving ends of the bus. Our experimental results show that, on average, the proposed encoding schemes improve the transition balancing capabilities of Thermal Spreading by a significant amount.