opensteno_qmk/tmk_core/protocol/chibios

TMK running on top of ChibiOS

This code can be used to run TMK keyboard logic on top of ChibiOS, meaning that you can run TMK on whatever ChibiOS supports. The notable examples are ARM-based Teensies (3.x and LC) and on the boards with STM32 MCUs.

Usage

• To use, get a zip of chibios and unpack/rename it to tmk_core/tool/chibios/chibios; or you can just clone the repo there. For Freescale/NXP Kinetis support (meaning ARM Teensies and the Infinity keyboard), you'll also need a zip of chibios-contrib, unpacked/renamed to tmk_core/tool/chibios/chibios-contrib. Likewise, for git-savvy people, just clone the repo there.
• Note: the abovementioned directories are the defaults. You can have the two chibios repositories wherever you want, just define their location in CHIBIOS and CHIBIOS_CONTRIB variables in your Makefile.
• You will also need to install an ARM toolchain, for instance from here. On linux, this is usually also present as a package for your distribution (as gcc-arm or something similar). On OS X, you can use homebrew with an appropriate tap.

Notes

• Some comments about ChibiOS syntax and the most commonly used GPIO functions are, as well as an example for ARM Teensies, is here.
• For gcc options, inspect tmk_core/tool/chibios/chibios.mk. For instance, I enabled -Wno-missing-field-initializers, because TMK common bits generated a lot of warnings on that.
• For debugging, it is sometimes useful disable gcc optimisations, you can do that by adding -O0 to OPT_DEFS in your Makefile.
• USB string descriptors are messy. 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.
• 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 (the built-in) bootloaders on STM32 works, but it is not entirely pleasant, since it is very much MCU dependent. So, one needs to dig out the right address to jump to, and either pass it to the compiler in the Makefile, or better, define it in <your_kb>/bootloader_defs.h. An additional startup code is also needed; the best way to deal with this is to define custom board files. (Example forthcoming.) In any case, there are no problems for Teensies.

Immediate todo

• power saving for suspend

Not tested, but possibly working

• backlight

Missing / not working (TMK vs ChibiOS bits)

• eeprom / bootmagic for STM32 (will be chip dependent; eeprom needs to be emulated in flash, which means less writes; wear-levelling?) There is a semi-official ST "driver" for eeprom, with wear-levelling, but I think it consumes a lot of RAM (like 2 pages, i.e. 1kB or so).

Tried with

• Infinity, WhiteFox keyboards
• all ARM-based Teensies
• some STM32-based boards (e.g. ST-F072RB-DISCOVERY board, STM32F042 breakout board, Maple Mini (STM32F103-based))

ChibiOS-supported MCUs

• Pretty much all STM32 chips.
• K20x and KL2x Freescale/NXP chips (i.e. Teensy 3.x/LC, mchck, FRDM-KL2{5,6}Z, FRDM-K20D50M), via the ChibiOS-Contrib repository.
• There is also support for AVR8, but the USB stack is not implemented for them yet (some news on that front recently though), and also the kernel itself takes about 1k of RAM. I think people managed to get ChibiOS running on atmega32[8p/u4] though.
• There is also support for Nordic NRF51822 (the chip in Adafruit's Bluefruit bluetooth-low-energy boards), but be aware that that chip does not have USB, and the BLE softdevice (i.e. Bluetooth) is not supported directly at the moment.

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.
• There is a working example of a STM32F042-based keyboard: firmware here and hardware (kicad) here. You can check this example firmware for custom board files, and a more complicated matrix than just one key.