You'll need to install an ARM toolchain, for instance from [gcc ARM embedded](https://launchpad.net/gcc-arm-embedded) website, or using your favourite package manager. After installing, you should be able to run `arm-none-eabi-gcc -v` in the command prompt and get sensible output. This toolchain is used instead of `avr-gcc`, which is only for AVR chips. Naturally you'll also need the usual development tools (e.g. `make`), just as in the AVR setting.
Next, you'll need ChibiOS. For Teensies, you'll need code from two repositories: [chibios-main](https://github.com/ChibiOS/ChibiOS) and [chibios-contrib](https://github.com/ChibiOS/ChibiOS-Contrib).
If you're not using git, you can just download a [zip of chibios from here](https://github.com/ChibiOS/ChibiOS/archive/a7df9a891067621e8e1a5c2a2c0ceada82403afe.zip), unpack the zip, and rename/move the unpacked directory (named `ChibiOS-<long_hash_here>`) to `tmk_core/tool/chibios/ChibiOS` (so that the file `tmk_core/tool/chibios/ChibiOS/license.txt` exists). Now the same procedure with a [zip of chibios-contrib from here](https://github.com/ChibiOS/ChibiOS-Contrib/archive/e1311c4db6cd366cf760673f769e925741ac0ad3.zip): unpack and move `ChibiOS-Contrib-<long_hash_here>` to `tmk_core/tool/chibios/ChibiOS-Contrib`.
If you're using git, you can just clone the two repos inside `tmk_core/tool/chibios`: [chibios](https://github.com/ChibiOS/ChibiOS) and [chibios-contrib](https://github.com/ChibiOS/ChibiOS-Contrib).
(Why do we need chibios-contrib? Well, the main repo focuses on STM32 chips, and Freescale/NXP Kinetis chips are supported via the Contrib repository.)
It's set up for Teensy LC. To use 3.x, you'll need to edit the `Makefile` (and comment out one line in `mcuconf.h`). A sample makefile for Teensy 3.0 is provided as `Makefile.3.0`, can be used without renaming with `make -f Makefile.3.0`. Similarly for Teensy 3.2, there's `Makefile.3.2`.
The USB support for Kinetis MCUs is due to RedoX. His ChibiOS fork is also [on github](https://github.com/RedoXyde/ChibiOS); but it doesn't include Teensy LC definitions.
Currently only the more fancy suspend features are not there (power saving during suspend). The rest should work fine (reports either way are welcome).
The notes below explain what commands can be used to examine and set the status of Teensy pins.
## ChibiOS pin manipulation basics
### Pins
Each pin sits on a "port", each of which comprises at most 32 individual pins.
So for instance "PTC5" from Kinetis manual/datasheet refers to port C (or GPIOA), pin 5. Most functions dealing with pins take 2 parameters which specify the pin -- the first being the port, the second being the pin number.
Within ChibiOS, there are definitions which simplify this a bit for the Teensies. `TEENSY_PINn_IOPORT` represents the port of the MCU's pin connected Teensy's PIN `n`, and `TEENSY_PINn` represents its MCU's pin number.
### Mode
A MCU pin can be in several modes. The basic command to set a pin mode is
The last parameter is the mode. For keyboards, the usual ones that are used are `PAL_MODE_INPUT_PULLUP` (input with a pullup), `PAL_MODE_INPUT_PULLDOWN` (input with a pulldown), `PAL_MODE_INPUT` (input floating, a.k.a. Hi-Z), `PAL_MODE_OUTPUT_PUSHPULL` (output in the Arduino sense -- can be then set HIGH or LOW).
### Setting
Pins are set HIGH (after they've been put into `OUTPUT_PUSHPULL` mode) by
All the commands that are available for pin manipulation through ChibiOS HAL are documented in [ChibiOS PAL driver docs](http://chibios.sourceforge.net/docs3/hal/group___p_a_l.html).