Well, search seems to be broken again on the site. Hopefully a dev will see this come across their screen and know how to fix it. I searched the site for "multiple definition" and 'premain' but neither one got ANY hits, even this topic itself! So if you tried to search the site to see if anyone else had had this problem before, it wouldn't have much chance of success. Anyway, all that is to say that we've run into this before. I'll link below here the thread where I managed to get around it. I'm not sure if there were other threads, but this one should give you some info on how to fix it for yourself. I could find this by going into the history of posts I had made, since search was failing me.... https://forum.mysensors.org/topic/10193/stm32f103c8-problem-at-compilation