RISC-V is a novel open instruction set architecture that supports multiple platforms while maintaining simplicity and reliability. Despite its novelty, the software support for RISC-V has been increasing in the last years, given that popular toolchains and operating systems already have support for RISC-V. However, although many works have been exploring the RISC-V software ecosystem, no work that raised the current state of software support for RISC-V is available. In this context, this survey reviews the contributions introduced in the last years to understand the RISC-V’s software ecosystem and its usage in both academic and industrial environments. We classified and evaluated the works into four main categories: application fields, RISC-V implementations, software architecture, and deployment features. The primary goal of this research is to provide the community with a comprehensive overview of the current state of RISC-V software support and identify and highlight the main contributions from recent work.

Embedded processors have been used in a diversity of applications, such as consumer electronics, home appliances, and automation systems. Another area that embedded processors can be adopted is space systems, which demand faulttolerant components to deal with the environmental hostility. This work presents a low-cost fault-tolerant implementation of the RISC-V architecture, an emerging open industry standard for the building of embedded processors. The proposed implementation employs physical and information redundancy to reduce error propagation, with competitive silicon and power overheads when comparing with other RISC-V implementations.

Recent research has shown interest in adopting the RISC-V processors for high-reliability electronics, such as aerospace applications. The openness of this architecture enables the implementation and customization of the processor features to increase their reliability. Studies on hardened RISC-V processors facing harsh radiation environments apply fault tolerance techniques in the processor core and peripherals, exploiting system redundancies. In prior work, we present a hardened RISC-V System-on-Chip (SoC), which could detect and correct radiation-induced faults with limited fault awareness. Therefore, in this work, we propose solutions to extend the fault observability of the SoC implementation by providing error detection and monitoring. For this purpose, we introduce observation features in the redundant structures of the system, enabling the report of valuable information that supports enhanced radiation testing and support the application to perform actions to recover from critical failures. Thus, the main contribution of this work is a solution to improve fault awareness and the analysis of the fault models in the system. In order to validate this solution, we performed complementary experiments in two irradiation facilities, comprehending atmospheric neutrons and a mixed-field environment, in which the system proved to be valuable for analyzing the radiation effects on the processor core and its peripherals. In these experiments, we were able to obtain a range of error reports that allowed us to gain a deeper understanding of the faults mechanisms, as well as improve the characterization of the SoC.

Reducing component size and increasing the operating frequency of integrated circuits makes the Systems-on-Chip (SoCs) more susceptible to faults. Faults can cause errors, and errors can be propagated and lead to a system failure. SoCs employing many cores rely on a Network-on-Chip (NoC) as the interconnect architecture. In this context, this study explores alternatives to implement the flow regulation, routing, and arbitration controllers of an NoC router aiming at minimizing error propagation. For this purpose, a router with Finite-State Machine (FSM)-based controllers was developed targeting low use of logical resources and design flexibility for implementation in FPGA devices. We elaborated and compared the synthesis and simulation results of architectures that vary their controllers on Moore and Mealy FSMs, as well as the Triple Modular Redundancy (TMR) hardening application. Experimental results showed that the routing controller was the most critical one and that migrating a Moore to a Mealy controller offered a lower error propagation rate and higher performance than the application of TMR. We intended to use the proposed router architecture to integrate cores in a fault-tolerant NoC-based system for data processing in harsh environments, such as in space applications.

Systems for harsh environments often use embedded processors for tasks that require reliability. However, harsh environments cause faulty behavior in electronics, which eventually lead to system failure. Therefore, embedded processors must use techniques to improve their reliability. In this context, this work presents the implementation and characterization of a RISC-V-based system-on-chip. We characterized our implementation by carrying out test campaigns at the ChipIr irradiation facility. This facility provides a beamline for testing electronics against neutrons, mimicking atmospheric-like environments. With this first test campaign, we identified the most critical parts of our system-on-chip and essential tips to improve the test effectiveness. In the second test campaign, we used an improved version of the system setup with higher reliability error observability features. The version embedding all the hardening techniques could correct or mitigate 98.1 % of the detected upsets under irradiation.