In healthcare, anomaly detection has emerged as a central application. This study presents an ultra-low power processor tailored for wearable devices dedicated to anomaly detection. Introducing a unique Day-Night architecture, the processor is bifurcated into two distinct segments: The Day segment and the Night segment, both of which function autonomously. The Day segment, catering to generic wearable applications, is designed to remain largely inactive, awakening only for specific tasks. This approach leads to considerable power savings by incorporating the Main-CPU and system interconnect, both major power consumers. Conversely, the Night segment is dedicated to real-time anomaly detection using sensor data analytics. It comprises a Sub-CPU and a minimal set of IPs, operating continuously but with minimized power consumption. To further enhance this architecture, the paper presents an ultra-lightweight RISC-V core, All-Night core, specialized for anomaly detection applications, replacing the traditional Sub-CPU. To validate the Day-Night architecture, we developed a prototype processor and implemented it on an FPGA board. An anomaly detection application, optimized for this prototype, was also developed to showcase its functional prowess. Finally, when we synthesized the processor prototype using 45 nm process technology, it affirmed our assertion of achieving an energy reduction of up to 57%.

The increasing interest in RISC-V from both academia and industry has motivated the development and release of a number of free, open-source cores based on the RISC-V instruction set architecture. Specifically, the use of lightweight RISC-V cores in processors tailored for IoT endnode devices is on the rise. As the range and complexity of these applications grow, there is an increasing demand for multicore processors that can handle floating-point operations. This poses a significant challenge because most lightweight RISC-V cores are integer cores lacking a floating-point unit (FPU). This limitation makes it difficult to design processors optimized for applications that require floating-point operations concurrently with integer operations. While it is inefficient to have a dedicated FPU per core in a multicore processor (because it would give rise to unnecessary power consumption), it is crucial to find a solution that balances performance and energy efficiency. To address this challenge, we propose to utilize an external lightweight FPU that can be added to any RISC-V integer core, along with a low-power multicore architecture that shares the said FPU. We have applied this concept to design a RISC-V processor that integrates these technologies, implemented it on an FPGA device, and completed the fabrication of a System-on-Chip for functional verification. Our experiments, which involved testing various applications on different processor prototypes, demonstrated significant energy savings of up to 79.6% in a quad-core processor prototype, highlighting the potential energy efficiency of our proposed technology.

This paper aims to develop an ultra-low power processor for wearable devices for anomaly detection. To this end, this paper proposes a processor architecture that divides the architecture into a part for general applications running on wearable devices (day part) and a part that performs anomaly detection by analyzing sensor data (night parts), and each part operates completely independently. This day-night architecture allows the day part, which contains the power-hungry main-CPU and system interconnect, to be turned off most of the time except for intermittent work, and the night part, which consists only of the sub-CPU and minimal IPs, can run all the time with low power. By developing a processor based on the proposed processor architecture, the design verification of the proposed technology and the superiority of power saving are demonstrated.

As applications running on lightweight RISC-V processors become increasingly diverse and complex, the need for multicore processors supporting floating-point units (FPUs) is riseing, making processor designs using existing open-source RISC-V cores challenging. With the exception of a very few, most open lightweight RISC-V cores are integer cores without FPUs, which greatly reduces the design exploration space, making it impossible to design a processor optimized for each application. For example, most of these applications mainly perform integer operations, but occasionally perform floating-point operations. For them, a multicore processor with FPU per core is overkill and wastes power, which is a critical problem for processors where low-power design is paramount. To address the problem, we propose an external lightweight FPU that can be attached to any RISC-V integer core and a low-power multicore architecture using the designed FPU. For verification, we designed a RISC-V processor that implements all the proposed technologies, prototyped it on an FPGA device, and finally fabricated it as a System-on-Chip. Through experiments, it was confirmed that the proposed technology can cut energy consumption energy by up to 23%.