Tau is a bare-metal operating system for the Raspberry Pi. Tau has zero external dependencies and runs directly from boot on the Raspberry Pi. Tau is written in a mix of ARM assembly and C++11 but does not link against libc or libc++.

Currently, Tau supports a limited number of the peripherals available on the Pi. Over time, we'd like to add support for more peripherals, including the USB and video controllers.

Tau supports a Linux host environment. Tau has been tested using Ubuntu 12.04, but most Linux host environments should work.

The first step is to install Chromium's depot_tools. We use depot_tools to pull in our other dependencies (e.g., gn).

Once you've installed depot_tools, create a .gclient file in an empty directory with the following contents:

solutions = [{
  'managed': False,
  'name': 'src',
  'url': 'git@github.com:abarth/tau.git',
  'deps_file': 'DEPS',
}]

Now, run gclient sync to pull down this repository and its dependencies.

The toolchain for building Tau is not managed with gclient. Instead, you'll need to build and install the toolchain using the instructions in the toolchain directory. In the future, we would like to use gclient to make the toolchain dependency hermetic.

Tau uses a ninja-based build system generated with gn. To build Tau, we first need to create the ninja files:

• gn gen out

We can then use ninja to build the system:

• ninja -C out

To run the examples, you'll need a Raspberry Pi, a MicroSD card, and a (ideally) a serial cable. To run the LED example, copy led.img to your MicroSD card, overwriting the kernel.img file. Note: When you copy led.img to your MicroSD card, you'll need to rename it to kernel.img in order for the Pi's boot process to find it.

Tau is available under a BSD-style license that can be found in the LICENSE file.

Special thanks to David Welch and Rene Stange. Their example bare-metal systems for the Raspberry Pi have saved me an immeasurable amount of heartache.