Memory access scheduling and binding considering energy minimisation in multi-bank memory systems: integrated approach

Memory-related activity is one of the major sources of energy consumption in embedded systems. Many types of memories used in embedded systems allow multiple operating modes (e.g. active, standby, nap, power-down) to facilitate energy saving. Furthermore, it has been known that the potential energy saving increases when the embedded systems use multiple memory banks in which their operating modes are controlled independently. The authors propose a compiler-directed integrated approach to the problem of maximally utilising the operating modes of multiple memory banks by solving the three important tasks simultaneously: (1) assignment of variables to memory banks, (2) scheduling of memory access operations and (3) determination of operating modes of banks. Specifically, for an instance of tasks 1 and 2, the authors formulate task 3 as a shortest path (SP) problem in a network and solved it optimally. Then, an SP-based heuristic that solves tasks 2 and 3 efficiently in an integrated fashion is developed. Then the proposed approach is extended to address the limited register constraint in the processor. From experiments with a set of benchmark programs, it is confirmed that the proposed approach is able to reduce the energy consumption by 15.76% over that by the conventional approach.