"Robin Mueller: I don't think I'..." <- Funny thing: I can not re-produce it in a simple MCVE. I have found out the following for my UART example code Debug image with hw mul: Works Debug image with 32bit mul: Becomes stuck in weird loop, jumps back to previous code in main when stepping through UART clock calculations Release image: Both work So maybe this is just some bug related to running out of RAM, and not the HW mult support at all? the debug apps are sketchy anyway. I had to use optimization level 1 at the very least, or the RAM would overflow and I can not even compile a really simple app. I am really curious what takes up so much RAM space, so I will probably dig a bit more here..