Increasing the energy efficiency of microcontroller platforms with low-design margin co-processors

Reducing the energy consumption in low cost, performance-constrained microcontroller units (MCU's) cannot be achieved with complex energy minimization techniques (i.e. fine-grained DVFS, Thermal Management, etc), due to their high overheads. To this end, we propose an energy-efficient, multi-core architecture combining two homogeneous cores with different design margins. One is a performance-guaranteed core, also called Heavy Core (HC), fabricated with a worst-case design margin. The other is a low-power core, called Light Core (LC), which has only a typical-corner design margin. Post-silicon measurements show that the Light core has a 30% lower power density compared to the Heavy core, with only a small loss in reliability. Furthermore, we derive the energy-optimal workload distribution and propose a runtime environment for Heavy/Light MCU platforms. The runtime decreases the overall energy by exploiting available parallelism to minimize the platform's active time. Results show that, depending on the core to peripherals power-ratio and the Light core's operating frequency, the expected energy savings range from 10 to 20%.