On 02/12/2021 17:06, Sébastien Gendre wrote: > Hello David, > > Thanks for your reply. > > Writing a firmware from scatch and not using the official IDE is the > challenge. > > It's based on this video of Nikolay Kondrashov who do the same thing for > another microcontroller with the same arch: > https://media.ccc.de/v/ASG2019-161-microcontroller-firmware-from-scratch > > I started by reading the arch and microcontroller manuals to see how its > start, how the memory are mapped, which clock and peripherals are > enabled after a reset, etc. > OK - but again, this is not the list for such things, as you are not facing gcc issues. I had a look at some of that video (not all of it as yet). I can agree that it can be fun and educational to do things from scratch, and see how things fit together at the lowest level. But I don't think you should start there. And it is wrong to suggest that this is all somehow necessary in order to use open source tools - when you use vendor-supplied tools these days, the solid majority of the parts are open source. They are simply put together by the vendor. Also note that if you are trying to run code directly from the reset vector, you don't have a full C environment. Your static data is not initialised or zeroed. Functions such as "printf" are unlikely to work. If you are using C++, static constructors or initialisers that require functions are not run. The reset vector is useful for things that need to be initialised before this - perhaps enabling clocks, memories, etc. It is not appropriate for "real" code.
