Hm~ on the off chance it's obvious to someone: I'm trying to use the built-in I2C hardware in STM32Lsomething. I use RIOT-OS's library for interacting with that I2C hardware, and what happens is that as soon as the pins are switched to the alternate function of I2C they get pulled down (afterwards it seems that no I2C operations ever complete, but that's not that weird considering this messed up initial state). Is there something obvious I could be doing wrong, or something I ought to check?