In the previous log entry I described that hardware was more or less working and I could have continued with writing firmware. That was 2 years ago and there has been little progress. So I decided to change approach for something that will require less effort and produce usable result sooner.
One possibility could be replacing atmega8 with something that is pin compatible with more memory and use QMK. It seems that QMK support isn't great, at least it's not their primary platform, so I am not keen on this idea. If am moving away from minimalist approach and trying to squeeze too much in functionality in mcu that is too small for that I might as well go with overkill and use something more powerful.
First idea was using teensy 3.5 or 3.6. Turns out ChibiOS support for them is somewhat incomplete. I am also not a fan of proprietary bootloader chip which prevents debugging. Printf debugging isn't an option if you can't initialize the hardware properly. I might return to this once I have a working keyboard.
Together with teensy I had ordered some Blue Pill boards. So this seemed like next best thing. It doesn't have enough pins for controlling the keyboard matrix directly but I can use the shift registers that I planned to use in Initial iteration. Next problem is that TPIC6C595 I had only operates at 5v. After a few hours of searching catalogs I found NPIC6C596ADJ. I could probably make a level shifter from transistors I have laying around but I will need to solder a new board anyway and there are other parts of software that can be worked that I can work in while the new parts arrive.