Install [the Newlib GNU RISC V toolchain](https://github.com/riscv/riscv-gnu-toolchain#installation-newlib) and do `make` to build. Do `make run` to run. It should print out a bunch of debug information related to OpenSBI and then a single `a`.
If you'd like to trace the execution since the beginning, uncomment the `# -S` at the end of the line in the makefile and run. This halts the emulator until a gdb connection is established.