I have updated the "NucleoSynth" project to be directly driven by the sliders and keyboard of the Yamaha Reface CS.
Here is the link to the project.
NucleoSynth Virtual Analog Synth Project
The project can be loaded onto either NUCLEO-F746ZG or NUCLEO-F767ZI STM32 Nucleo-144 development boards, and the Reface can be plugged directly into the USB port on the boards.
I chose to purchase the Reface CS because of it's portability, playability, and abundance of slider controllers, making it a great controller keyboard to use with the NucleoSynth project.
As an extra bonus, I can unplug it from the NucleoSynth board, and play the absolutely wonderful AN sound engine that the Reface CS contains. As a past owner of the Yamaha AN1x, I still have not heard a more convincing Virtual-Analog synthesis engine anywhere.
The NucleoSynth project is just that, a project. It is not a replacement to any synth on the market, it is merely an experiment in what a $23 development board can accomplish. It has obvious limitations (6-voice polyphony, Saw/Square waves only for all 12 oscillators, no FM, no hard-sync, aliasing on the top octaves, etc.), but it does have Key-Follow for VCF and ENV, and also responds to the Reface's Velocity-Sensitive keyboard.