Bonsai-C VS qmk_firmware

right, but I cannot find a compatible replacement that has more memory proton-c is out of stock everywhere, Bonsai-C would have to be custom printed -- I don't see any ready source for it. The STM32F401CC blackpill is available and cheap, but not compatible with PCBs designed for the pro micro. Other compatible MCUs like the Puchi-C and Elite-C have the same memory as the pro micro.

I have read the information on using a Bonsai C4 with split keyboards and think I understand it, but wanted to check with the community. Bonsai C4 Github

Github link

GitHub link: https://github.com/customMK/Bonsai-C/tree/main/C4

In addition to the connections to the switch matrix, you'll obviously have connections, to the USB port (which also conveniently supplies power and ground) and you may even have some ESD protection devices. Here's a schematic for a similar controller card (but powered by an ARM chip): https://github.com/customMK/Bonsai-C

Yeah, the Teensy is a great option for handwiring, or if additional pins are needed for extra features like encoders. I can't help but wonder, however, if the future belongs to ARM. QMK's own Proton C uses a big manly ARM chip with a stupid amount of flash, RAM and ridiculous clock speeds. And then there is the Bonsai C, which is an optimized version of the Proton C: https://github.com/customMK/Bonsai-C

Absolutely! We linked to it in the main comment under this post and prominently feature it in the GitHub repo, but for your convenience, I can link it here too. Enjoy!

I have only quickly tested it and it works as far as I can tell so far. I implemented it on top of achordion, because I use it anyway and it was quite simple to add on top of it. Maybe you still find the change interesting.

Yes, LTO_ENABLE is on and confirmed working. I just have a couple of features I'd like to use (Getreuer's accordion and layer lock -- love it!, tap dance, mouse keys, combo, leader...). My test config is here, but not functional yet, so you may see that I have for example mouse keys enabled but not used yet, but I probably will use it at some point, so I keep it enabled for now. I'm sure there is room for optimizations, but I guess I'm also spoiled by MCUs with more memory and would prefer to not have to worry about memory at all :)