Reducing transitions on memory buses using sector-based encoding technique

In this paper, we introduce a class of irredundant low power encoding techniques for memory address buses. The basic idea is to partition the memory space into a number of sectors. These sectors can, for example, represent address spaces for the code, heap, and stack segments of one or more application programs. Each address is first dynamically mapped to the appropriate sector and then is encoded with respect to the sector head. Each sector head is updated based on the last accessed address in that sector. The result of this sector-based encoding technique is a reduction in the number of bus transitions when encoding consecutive addresses that access different sectors. Our proposed techniques have small power and delay overhead when compared with many of the existing methods in the literature. One of our proposed techniques is very suitable for encoding addresses that are sent from an on-chip cache to the main memory when multiple application programs are executing on the processor in a time-sharing basis. For a computer system without an on-chip cache, the proposed techniques decrease the switching activity of data address and multiplexed address buses by an average of 55% and 67%, respectively. For a system with on-chip cache, up to 55% transition reduction is achieved on a multiplexed address bus between the internal cache and the external memory. Assuming a 10 pF per line bus capacitance, we show that power reduction of up to 52% for an external data address bus and 42% for the multiplexed bus between cache and main memory is achieved using our methods.