NOTE: this README is just a draft, the repo is under heavy rework.
Factory Raspberry Pi is defined as "low-cost, high performance, desktop computer" or "personal computer" or "single board computer". With a few exceptions (ie: Compute Module and Pico), it is made to hook a monitor, keyboard and mouse, and give a graphical interface to the users. In time it has been successfully used for many different electronic projects (motion control, radio, lightning) but its use in electronics was limited in software because of the different scope.
The Broadcom silicon is a VideoCore GPU (VC4 on RPi0-3, VC6 on RPi4) made of VPUs (general purpose cores), QPUs (vector cores), and an ARM CPU. Factory firmware focuses on desktop use, giving to the users the chance to load Linux on the ARM cpu and keeping the GPU for maintenance and video output, using a closed source ThreadX operating system running in the background on the VPUs. This setup limits both the real time performance and the general purpose GPU computing (GPGPU). By replacing ThreadX with an open source alternative, users are able to fully exploit RPi hardware, turning any RPi in a "low-cost, high performance, electronics power house": Metal-Pi.
Metal-Pi is a bare metal development platform for all Raspberry Pi models. It is an extension of Kristina Brooks's rpi-open-firmware and Michael Bishop's followups (rpi-open-firmware, LK). It is tailored by developers for developers: headless, using the gpu (ie: 2 VPUs and 12 QPUs) for real time applications and general purpose computing (GPGPU).
This repository is the umbrella project packing all the different parts of the project. The build process produces an example platform but, being 100% open source, any part can be replaced, and the firmware itself can be modified to fit your own needs.
See the status file for more info about current features.
First you need to install Nix:
curl -L https://nixos.org/nix/install | sh
This will create the Nix's store at /nix and setup the command line utility in your path. Then you need to download a copy of this repo
git clone --recurse-submodules https://github.com/mfp20/metalpi.git
finally chdir to your local copy of this repo and
nix-build -f . arm6.bootdir
This will download and build the toolchain and the firmware. After completion copy result folder's contents on the SD card,
move the SD card to your RPi and boot!
For more info about installing and building Metal-Pi see the install file.
This repository includes Nix-based scripts and all the submodules needed to setup the toolchain and build the default distribution.
The build process will download, build and pack a ready to use folder to be copied on your SD card. It will include:
- the libre replacement for the stock
bootcode.binnormally loaded from the SD card by Raspberry Pi. Stage1 initializes PLLC and moves VPU0 over to it, brings up UART, performs SDRAM initialization, mapping it to0xC0000000(uncached alias), and loads LittleKernel running on VPU0. Stage2 initializes the ARM core, maps itself to ARM address0x0, and run the selected payloads for the available cores, - the Metal-Pi C++ Platform Abstraction Library (docs),
- the Metal-Pi Linux tools (docs) linux command line tools.
A text file in the output directory (ie: SD card content) is used to tweak the runtime options. User can select what kind of payload to run on startup:
- GPGPUd: runs on VPU0 as a thread, but can spawn a secondary thread on VPU1 to fully exploit QPUs,
- GPIOd: runs on VPU1 to manage the GPIO I/O using DMA and PWM devices,
- Linux: runs on ARM,
- Micropython: runs on ARM.
You can find all available help in the docs folder.
Metal-Pi is the result of many people's work. For details see the authors file.
Our code is under GPLv2+. Various external projects are mirrored under a mix of GPL-compatible licenses. Broadcom's code is licensed under 3-Clause BSD License.
Please contact us before randomly hacking on the codebase.