Attempt to add STM32F4xx

[RussellHaley]

Hi,

First: I'm not a firmware developer, I just muck around in firmware.

I'm attempting to bring in an existing STM32F466ret (?) based project in polymcu. Our project uses the Std Periph library, not the HAL. I was able to put our source code into the application folder and get it to start the build. I then turned my attention to the board/device support and started to notice some differences.

The CMSIS/core/include folder in polyMCU has a newer set of files from my download from STM32. That is confusing alone. Yours is v5.00, the currrent std periph download is 4.10. Also there are different files, some that are present in the F4 package. Notably core_cmSimd.h, core_cmFunc.h, core_cmInstr.h.

I don't know how to handle all these mismatches. Thoughts? Thanks for the neat tool!