This piece of software converts PS/2 keyboard signal into USB HID reports so wonderful mechanical keyboards from the past can function in our modern world.
On every PS/2 clock pin's falling edge the incoming bit is handled. Some sanity checks are performed on the incoming data and if everything is alright, the 8-bit keycode is put into a queue.
In the main loop the queue is handled (if it's full or after a short timeout).
PS/2 scancodes are mapped onto corresponding USB codes and a HID report is sent.
If I2C handle is not NULL, the codes are also sent to the slave device for
further processing (there's a little arduino script in the hud folder which
flashes some LEDs on every keystroke).
The initialization code has been generated with Cube MX. Unfortunately, every
generation erases the modified usbd_hid.c file. After the code generation,
files from hid folder must be copied into the
Middlewares/ST/STM32_USB_Device_Library/Class/HID folder.
You can build and upload the project using build.zsh script (it handles
this "hid" situation).
I didn't put the Drivers and other files generated with Cube into the
repository so you'll have to regenerate the project by yourself. Just open
ps2-to-usb.ioc with Cube MX and you'll be good.
I use STM32F072C8 for this project but any STM32 with an USB peripheral will suffice (some pin remapping can be needed).
Mind that the Caps Lock key is mapped to ESC because i use Vim and Left Alt
is mapped to Meta because I use macOS. You can change that in keymap.c.
Files you should concern when modifying the code:
keyboard.hkeymap.hqueue.hmain.c
There's not much left to do other than the lock key LEDs are not handled. I do not really need that but feel free to contribute.