QSOE/N, part 3: first boot on the HiFive Unmatched

Part 2 left QSOE/N as a working operating system that had only ever run in QEMU. This post is the jump to real silicon — a SiFive HiFive Unmatched (FU740) on my desk — and the five obstacles between "boots fine in the emulator" and an interactive shell on real hardware. The recurring theme is that QEMU is generous in ways the FU740 is not. Every fix below is a thing the emulator either did for me…