## USB stack implementation using ChibiOS

### Notes

- To use, unpack or symlink ChibiOS here, to `chibios`.
- For gcc options, inspect `chibios.mk`. For instance, I enabled `-Wno-missing-field-initializers`, because TMK common bits generated a lot of hits on that.
Also pay attention to `-O0` (enabled for debugging); for deployment use `-O2`.
- USB string descriptors are a mess. I did not find a way to cleanly generate the right structures from actual strings, so the definitions in individual keyboards' `config.h` are ugly as heck.
- There are some random constants left so far, e.g. 5ms sleep between calling `keyboard_task` in `main.c`. There should be no such in `usb_main.c`. Everything is based on timers/interrupts/kernel scheduling (well except `keyboard_task`), so no periodically called things (again, except `keyboard_task`, which is just how TMK is designed).
- It is easy to add some code for testing (e.g. blink LED, do stuff on button press, etc...) - just create another thread in `main.c`, it will run independently of the keyboard business.
- Jumping to bootloader works, but it is not entirely pleasant, since it is very much MCU dependent. The code is now geared towards STM32 chips and their built-in bootloaders. So, one needs to dig out the right address to jump to, and pass it to the compiler in the `Makefile`. Also, a patch to upstream ChibiOS is needed (supplied), because it `ResetHandler` needs adjusting.
- Sleep LED works, but at the moment only on/off, i.e. no breathing.
- The USB stack works pretty completely; however there are bits of other TMK stuff that are not done yet:

### Immediate todo

- power saving for suspend?
- PWM for sleep led

### Not tested, but possibly working

- backlight

### Missing / not working (TMK vs ChibiOS bits)

- eeprom / bootmagic (will be chip dependent; eeprom needs to be emulated in flash, which means less writes; wear-levelling?)

### Tried with

- ChibiOS 3.0.1 and ST F072RB DISCOVERY board.
- Need to test on other STM32 chips (F3, F4) to make it as much chip-independent as possible.