I have a project with a SAMD51 that crashes within the first few seconds of a restart. It uses an external 32k oscillator connected to xosc32k through PA0 and PA1, this is fed into DPLL0 running at 120MHz (with 0xe4d as the lower divider ratio integer), which then goes into GCLK0 and to the CPU. GCLK3 is fed from XOSC32k at 32.768khz, which feeds DFFL48, which then goes into GCLK1 to the USARTs and USB.
This seems to be fairly simple as compared to other Samd51 projects I've looked at.
I am aware of the SamD51 errata where you need to use LBYPASS; this seems to be done in the adafruit code everyone steals, but I have no idea how to configure this with START. I think this could be done in hri_oscctrl_d51.h, but.... I have no idea where. This doesn't really make much sense, though, because these library files are downloaded from the Internet, and Microchip _could_ just fix these library files to include fixes from the errata, so that's probably a red herring anyway.
Has anyone used START to configure a SAMD51 to run at 120MHz? I see references to it on this board, but no code.