+- ChibiOS with Kinetis patches and Teensy LC and 3.0.
+
+## ChibiOS-supported MCUs (as of 3.0.2)
+
+- Pretty much all STM32 chips.
+- There is some support for K20x and KL2x Freescale chips (i.e. Teensy 3.x/LC, mchck, FRDM-KL2{5,6}Z, FRDM-K20D50M), but again, no official USB stack yet. However the `kinetis` branch of [my ChibiOS fork](https://github.com/flabbergast/ChibiOS). With this fork, TMK work normally on all the ARM Teensies.
+- There is also support for AVR8, but the USB stack is not implemented for them yet, and also the kernel itself takes about 1k of RAM. I think people managed to get ChibiOS running on atmega32[8p/u4] though.
+- I've seen community support for Nordic NRF51822 (the chip in Adafruit's Bluefruit bluetooth-low-energy boards), but not sure about the extent.
+
+## STM32-based keyboard design considerations
+
+- STM32F0x2 chips can do crystal-less USB, but they still need a 3.3V voltage regulator.
+- The BOOT0 pin should be tied to GND.
+- For a hardware way of accessing the in-built DFU bootloader, in addition to the reset button, put another button between the BOOT0 pin and 3V3.
+- For breathing the caps lock LED during the suspended state ("sleep LED"), it is desirable to have that LED on a hardware PWM pin (there's usually plenty of those, look for TIMERs in the datasheet). However this is not strictly necessary, because instead of direct output of a timer to a pin (better of course), it is easy to define timer callbacks in ChibiOS that turn on/off an arbitrary pin.
+
+
+
+[ChibiOS]: http://chibios.org