Energy Characterization of a RTOS Hardware Accelerator for SoCs

During the last decade several Real-Time Operating System (RTOS) hardware accelerators have been proposed. The accelerators perform operating system functionality traditionally implemented in software. While their effects on predictability and speedups have been studied, their impact on system energy consumption is still unknown. As a first step towards comparison of energy efficiency between HW-RTOSs and SW-RTOSs, this paper presents an energy characterization of the different operating system calls offered for an in-house developed RTOS hardware accelerator called Real Time Unit (RTU). The obtained results show that a RTU consumes about 0.16 mW/MHz for a 1.8V 0.18micron process and that the power consumtion is independent of the function it performs. The power consumtion variances are within 4 percent of the average value. Even during the idle periods huge amount of power is wasted due to unwanted activity triggered by the clock. We believe that if a HW-based RTOS is to beat a SW-RTOS based system in terms of energy consumtion, power optimization techniques such as gated clocking needs to be used for the hardware accelerator.