STM32 support

[felipegaspari]

These boards are very cheap, powerful and some have a lot of IO, like STM32F4xxx. Would be great to have support for them!

[tttapa]

There's some discussion in this thread: https://forum.arduino.cc/t/control_surface-h-usage-on-stm32/686112

The main issue is the lack of a good (MIDI) USB backend for the official STM core, and the conclusion was the following:

The problem with the STM32 ecosystem is that there are way too many different chips out there and it seems like STM doesn't want to spend too much time money on Arduino compatibility (which is understandable, STM32 chips are targeted at professionals, those are the ones bringing in the money, not the occasional hobbyist that buys one or two development boards). As a result, the Arduino STM32 community seems quite fragmented and relying on the knowledge of a handful of developers that maintain the cores and libraries.

While there are some nice and cheap STM32-based “Arduino” boards available, I prefer paying a bit more for my boards if that means supporting a company like Arduino or PJRC (Teensy) that contributes to the ecosystem, software, libraries, community, support, etc.

If the STM32 situation improves in the future, I might take a second look, but for now, I don't think I want to get into that “mess”. Porting it once is not an issue per se, but providing support for an unstable platform for years to come is not something that I want to get into, you have to understand that I'm just one person maintaining a MIDI library in my (scarce) free time, I really can't take up the job of supporting STM32 USB MIDI firmware etc.

I'm willing to help anyone who wants to try porting Control Surface to STM32 by answering specific questions etc., and then I might include some of the fixes as “community supported but not officially supported”, but I don't have the time to do it myself (and maintain it afterwards).