NVPE: An FPGA-Based Non-Volatile Processor Emulator for Intermittent Computing ^†

Abstract

Research on novel memory storage devices that occupy less physical area and are compatible with CMOS processes, such as resistive RAM, has led to the interesting study of non-volatile compute memories and devices. The advent of these low-compromise non-volatile cells invites the opportunity for fully non-volatile microprocessors that are capable of rapid shutdown and startup. This class of microprocessors would be beneficial to intermittent computing systems applications that wait until an energy-harvesting device has sufficient energy available before they do some useful work due to requiring less energy to power down safely. Prior work has demonstrated the emulation of these non-volatile memories that enable the rapid testing of non-volatile memory systems. In this work, we expand on these ideas by introducing a framework that is capable of emulating fully functional non-volatile microprocessors based on individual non-volatile flip-flops, rather than larger addressable non-volatile memory blocks. Our proposed system enables the conversion and emulation of conventional systems into non-volatile equivalents. The proposed architecture is integrated into the open-source RISC-V microprocessor implementation ‘Potato’ and synthesized on a Xilinx Ultrascale+ XCZU5EV FPGA. The area overhead for the proposed emulator is 22 slice registers and 17 LUTs per emulated non-volatile flip-flop. As a case study, an AES block cipher is executed throughout power-down and power-up sequences. The system is shown to properly emulate the complex overhead operations resulting from sensitive power-down and power-up sequences in power-intermittent systems, providing a vital metric for the non-volatile microprocessor’s fidelity.