Arnold: an eFPGA-Augmented RISC-V SoC for Flexible and Low-Power IoT End-Nodes

A wide range of Internet of Things (IoT) applications require powerful, energy-efficient and flexible end-nodes to acquire data from multiple sources, process and distill the sensed data through near-sensor data analytics algorithms, and transmit it wirelessly. This work presents Arnold: a 0.5 V to 0.8 V, 46.83 uW/MHz, 600 MOPS fully programmable RISC-V Microcontroller unit (MCU) fabricated in 22 nm Globalfoundries GF22FDX (GF22FDX) technology, coupled with a stateof-the-art (SoA) microcontroller to an embedded Field Programmable Gate Array (FPGA). We demonstrate the flexibility of the System-OnChip (SoC) to tackle the challenges of many emerging IoT applications, such as (i) interfacing sensors and accelerators with non-standard interfaces, (ii) performing on-the-fly pre-processing tasks on data streamed from peripherals, and (iii) accelerating near-sensor analytics, encryption, and machine learning tasks. A unique feature of the proposed SoC is the exploitation of body-biasing to reduce leakage power of the embedded FPGA (eFPGA) fabric by up to 18x at 0.5 V, achieving SoA state bitstream-retentive sleep power for the eFPGA fabric, as low as 20.5 uW. The proposed SoC provides 3.4x better performance and 2.9x better energy efficiency than other fabricated heterogeneous re-configurable SoCs of the same class.