My code wasn't taking control of the lerdge, as I might have mentioned, and with a little bit of in-memory debugging, I determined that we never exit the clock setup. I cloned the arduino variant from the discovery 407, which means I basically ignored all the normal guidance - you're supposed to run the cube, generate a definition for the board,a nd copy the clock init out of that with all the appropriate peripherals set up.

I'm on a mac and having trouble getting it to run, so I'm looking closer at the hardware and not seeing the obvious style of crystal I"m used to on the lerdge-X. So tomorrow I'll probably go part by part until I figure out what it is. Then I can generate a proper definition and try again to get proper Arduino code running.