Working-zone encoding for reducing the energy in microprocessor address buses

The energy consumption due to input-output pins is a substantial part of the overall chip consumption. To reduce this energy, this work presents the working-zone encoding (WZE) method for encoding an external address bus, based on the conjecture that programs favor a few working zones of their address space at each instant. In such cases, the method identifies these zones and sends through the bus only the offset of this reference with respect to the previous reference to that zone, along with an identifier of the current working zone. This is combined with a one-hot encoding for the offset. Several improvements to this basic strategy are also described. The approach has been applied to several address streams, broken down into instruction-only, data-only, and instruction-data traces, to evaluate the effect on separate and shared address buses. Moreover, the effect of instruction and data caches is evaluated. For the case without caches, the proposed scheme is specially beneficial for data address and shared buses, which are the cases where other codings are less effective. On the other hand, for the case with caches the best scheme for the instruction-only and data-only traces is the WZE, whereas for the instruction-data traces it is either the WZE or the bus-invert with four groups (depending on the energy overhead of these techniques).