A DVS-based pipelined reconfigurable instruction memory

Energy consumption is of significant concern in battery operated embedded systems. In the processors of such systems, the instruction cache consumes a significant fraction of the total energy. One of the most popular methods to reduce the energy consumption is to shut down idle cache banks. However, we observe that operating idle cache banks at a reduced voltage/frequency level along with the active banks in a pipelined manner can potentially achieve even better energy savings. In this paper, we propose a novel DVS-based pipelined reconfigurable instruction memory hierarchy called PRIM. A canonical example of our proposed PRIM consists of four cache banks. Two of these cache banks can be configured at runtime to operate at lower voltage and frequency levels than that of the normal cache. Instruction fetch throughput is maintained by pipelining the accesses to the low voltage banks. We developed a profile-driven compilation framework that analyzes applications and inserts the appropriate cache reconfiguration points. Our experimental results show that PRIM can significant reduce the energy consumption for popular embedded benchmarks with minimal performance overhead. We obtained 56.6% and 45.1% energy savings for aggressive and conservative VDD settings, respectively, at the expense of a 1.66% performance overhead.