Some of my students' projects in the 2020 autumn semester focused on exploring what is required to port existing small operating systems to the RISC-V architecture. The systems covered include Niklaus Wirth's Project Oberon as well as Plan 9 from Bell Labs and Inferno from Bell Labs and vita nuova.
Project report
Oberon RISC-V source code
Oberon RISC-V emulator source code