Ranging from circuit-level characterization to designing a platform architecture, developing a design automation tool, and fabricating a System on Chip (SoC), this article deals with the entire development process for ultralow-power (ULP) SoCs for Internet-of-Things (IoT) end nodes. More precisely, this article first focuses on the unique characteristics of the ULP circuits, the temperature effect inversion (TEI), i.e., the delay of the ULP circuits decreases with increasing temperature. Existing TEI-aware low-power (TEI-LP) techniques have incredible potential to further reduce the power consumption of conventional ULP SoCs, but there is a critical limitation to be widely adopted in real SoCs. To address this limitation and realize the ULP SoCs that can fully benefit from the TEI-LP techniques, this article proposes a new TEI-inspired SoC platform (TIP) architecture. On top of that, taking into account that the highly complex, time consuming, and labor-intensive development process of these ULP SoCs may hinder their widespread use for IoT end nodes, this article presents a new electronic design automation tool to accelerate ULP SoC development, RISC-V express (RVX). Finally, by using the RVX, this article introduces a TIP prototyping chip fabricated in 28-nm FD-SOI technology. This chip demonstrates that power savings of up to 35% can be achieved by lowering the supply voltage from 0.54 to 0.48 V at 25 • C and 0.44 V at 80 • C while continuing to operate at a target 50-MHz clock frequency.
With the advent of the Internet-of-Things (IoT) era, the demand for lightweight embedded systems is rapidly increasing. So far, ultra-low power (ULP) processors have been leading the development of lightweight embedded systems. However, as the IoT era gets more sophisticated, existing ULP processors are expected to reach a critical limit in the absence of a memory management unit (MMU) in that multiple programs cannot be run in the MMU-less embedded systems. To tackle this issue, we propose an architecture in which the MMU is embedded in a network-on-chip (NoC). Through the proposed approach, NoC offers MMU functionality without modifying the processor design, allowing developers to easily leverage the existing ULP lightweight processors and build embedded systems that support multiprocessing. In this paper, along with the details of the proposed MMU-embedded NoC (MMNoC) design, a prototype platform including the MMNoC and dual RISC-V processors is provided. The prototype platform is synthesized with FPGA and Samsung 28 nm FD-SOI technology to verify the functional accuracy and small performance, area, and power overhead of the MMNoC. INDEX TERMS Network-on-chip, NoC, memory management unit, MMU, embedded system.
RISC-V has been experiencing explosive growth since its first appearance in 2011. Dozens of free and open cores developed based on this instruction set architecture have been released, and RISC-V based devices optimized for specific applications such as the IoT and wearables, embedded systems, AI, and virtual, augmented reality are emerging. As the RISC-V cores are being used in various fields, the demand for multicore platforms composed of RISC-V cores is also rapidly increasing. Although there are various RISC-V cores developed for each specific application, and it seems possible to pick them up to create the most optimized multicore for the target application, unfortunately it is very difficult to realize this in reality. This is mainly because most open cores are released in the form of a single core without cache coherence logic, which requires expensive design effort and development costs to address it. To tackle this issue, this paper proposes a method to solve the cache coherence problem without additional effort from the developer and to maximize the performance of the multicore composed of the RISC-V core selected by the developer. Along with a description of the sophisticated operating mechanisms of the proposed method, this paper details the architecture and hardware implementation of the proposed method. Experiments conducted through the prototype development of a RISC-V multicore platform involving the proposed architecture and development of an application running on the platform demonstrate the effectiveness of the proposed method.INDEX TERMS Multicore platform, RISC-V, system-on-chip (SoC), electronic design automation (EDA)
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