NarcOS - A bare metal ultralight kernel for Raspberry Pi 3 (BCM2837)

Introduction

The Raspberry Pi 3 is the newest and most powerful "Ras Pi" yet. It is a simple credit card sized ARM based computer capable of HDMI & Composite video output. It features a 1.2GHz Quad Core CPU with 1GB of RAM and a mighty VideoCore IV GPU. It also boasts of 4 USB 2.0 High Speed Ports, an Ethernet Port, 802.11 b/g/n WiFi Radio and Bluetooth.

Most use a Raspbian or Ubuntu image in an SD card to code in a Linux environment. You get Python out of the box on the terminal, what more does one need right?

There are a few ones still out there who want to go bare-metal on the BCM2837 SoC. What is bare-metal? In short, bare-metal is the hardware without an OS. All the code goes linux independent. No taken-for-granted libraries in C. Forget Python and all. Each and every movement of the processor is fully in your control, and in turn you have to compromise on having a secure, OS environment. If this sounds scary, then I think maybe I should tell you, it is what the dare devil programmers do.

First things first

Since it is compiled using GCC for ARM arm-none-eabi-gcc, it is machine independent. I personally built this on macOS. Anyhow, I'm gonna give the basic outline for ease of install

• Goto GNU ARM Embedded Toolchain Download and grab the appropriate archive.
• Open a terminal and cd to the Downloads folder where the tar was downloaded.
• You need MinGW if on Windows.
• Use sudo tar -xvf gcc-arm-none-eabi-XXXXX.tar.bz2 -C /usr/local/gcc-arm-none-eabi to untar the archive
• Append /usr/local/gcc-arm-none-eabi/bin to the $PATH variable for your shell. I echoed the line into my ~/.bash_profile for a permanent change. Use source ~/.bash_profile for $PATH update in your current shell immediately.
• Run arm-none-eabi-gcc --version on your shell. If it outputs a valid version, then congratulations, you have successfully installed a working toolchain for ARM.
• Clone this archive into a folder. I use /Documents/Experiments/ARM/NarcOS.

A little more preparation

If you already have an SD card with Raspbian or any other flavor of Linux installed then it already has the kernel7.img config.txt bootcode.bin and start.elf files in them. For our kernel to work, you simply need to replace the kernel7.img with our own kernel7.img.

Unfortunately if you don't, nothing to worry about. Download the files from here. Format the SD card with a FAT partition and place these files there.

You can modify the oscopy.sh to compile, copy and unmount the SD card.

On the road to bare-metal-ay

If you have completed all the steps above successfully, most probably your code will run. Currently it produces a weird pattern through HDMI and can blink an LED through GPIO18. It is a pretty basic example. It is under development.