Going bare metal on Raspberry Pi

Introduction:

If you're an avid Raspberry Pi enthusiast and have explored the world of traditional Linux-based development on the platform, it's time to embark on a new adventure. In this blog post, we'll delve into the exciting realm of bare metal C++ development for Raspberry Pi using Circle. Ever wanted precise real-time control Linux preventing you from getting? Boot up into your full application function in less than 3 seconds? We'll embark on an exciting journey of bare metal C++ development for Raspberry Pi using the Circle framework, unlocking the true potential of direct hardware access.

Understanding Bare Metal Development:

While operating systems provide convenience and feature-rich environments, they also introduce layers of abstraction that limit direct hardware control. Bare metal development allows us to interact with the Raspberry Pi's hardware at a much lower level, enabling us to tap into its full power and create highly optimized applications. By programming directly on the hardware, we can build custom software tailored to specific needs and explore interactions with custom hardware components. If you come from an MCU experience, you'll be delighted now you can have gigabytes of RAM under your control with the simplicity of Arduino code. 

Introducing CircleNetboot:

To enhance the bare metal development experience for Raspberry Pi, we'll utilize CircleNetboot. CircleNetboot is a small bootloader residing on the microsd card that allows us to boot our bare metal code directly from the network, eliminating the need to insert the physical media again and again, or load via the slower serial port. 

Setting up the Development Environment:

Let's walk through the steps to set up our development environment and leverage CircleNetboot for bare metal C++ development:

1. Raspberry Pi Setup: Begin by setting up your Raspberry Pi board (any model should work) with a power source, keyboard, mouse, and display. Ensure that you are familiar with Raspberry Pi's traditional Linux-based development environment.

2. Installing CircleNetboot: CircleNetboot can be installed on your sdcard, by visiting the CircleNetboot GitHub repository for a prebuilt image (https://github.com/probonopd/CircleNetboot/releases) and follow the installation instructions provided. You will will have a choice of HTTP or FTFP uploading; I suggest to plan starting with HTTP, as it only requires your browser pointed at the Pi.

3. Install Circle: Circle can be installed on your development machine, which can be running Linux, macOS, or Windows. Visit the Circle GitHub repository (https://github.com/rsta2/circle) and follow the installation instructions provided for your platform. You will also see an option developing without installing the toolchain, later, via the GitHub workflows.

4. Create a New Circle Project: Once Circle is installed, create a new project directory for your bare metal development. This directory will contain your source code and project configuration files.

5. Writing Your Bare Metal C++ Code: Create a new project directory for your bare metal development. Inside the project directory, write your C++ code, leveraging the Circle framework and its libraries for hardware interactions. Circle provides abstractions for GPIO pins, UART, timers, and more, simplifying the process of accessing Raspberry Pi's peripherals.

6. Building Your Code: Use the Circle build system to compile your bare metal C++ code and generate a raw binary image. Invoke the Circle build command (make) in your project directory to generate the binary file.

7. Preparing the Network Boot Infrastructure (Optional): At this point DHCP and the browser should be sufficient. If you'd like to discover more options, you can set up a bit more advanced network boot infrastructure, too. This typically involves configuring a TFTP server and DHCP server to serve the necessary files to the Raspberry Pi during boot.

8. Deploying and Running Your Bare Metal Code: Ensure that the Raspberry Pi is connected to the network and powered on. Transfer your generated binary image to the Raspberry Pi by uploading from your brower. The Raspberry Pi will then will jump into your uploaded binary, executing it on the hardware. If you want to make the completed application permanent on the scared, replace the CircleNetboot binary with yours. 

Exploring Further:

As you gain proficiency in bare metal development using Circle, consider exploring the following advanced topics:

1. Continuous Integration with GitHub Workflows: Streamline your development process by incorporating GitHub Workflows. Automate the build and deployment of your bare metal code by setting up GitHub Actions to generate binaries and card images whenever changes are pushed to your repository. This enables a seamless development workflow, ensuring that your bare metal code is always up to date and readily available for deployment. One example of this can be found in the CircleNetboot repo.

2. Generating SD Card Images: Instead of transferring individual binary files, you can create complete SD card images that contain your bare metal code, boot configuration, and any necessary dependencies. Explore tools and methodologies to generate custom SD card images that can be easily flashed onto SD cards for deployment on multiple Raspberry Pi devices. Also demonstrated in the CircleNetboot repo.

3. Advanced Peripheral Interactions: Dive deeper into interacting with Raspberry Pi's peripherals. Explore topics such as accessing and controlling advanced features like I2C, SPI, DMA, or even using hardware accelerators. GPU, anyone? Implement intricate communication protocols, develop drivers for custom hardware components, or integrate external sensors and modules into your bare metal applications.

4. Real-Time Systems: Delve into the realm of real-time systems and explore techniques for achieving deterministic behavior in your bare metal applications. Learn about task scheduling, interrupt handling, and multicore techniques to ensure timely responses to critical events.

5. Low-Power Optimization: Optimize your bare metal code to minimize power consumption and extend battery life in scenarios where power efficiency is crucial. Explore techniques such as power management, sleep modes, and fine-grained control over peripheral usage to maximize energy efficiency.