• Bare Metal Programming on Rpi 3

https://github.com/bztsrc/raspi3-tutorial

• GPIO support for Rpi Ubuntu images

https://alioth-lists.debian.net/pipermail/pkg-raspi-maintainers/Week-of-Mon-20190318/000333.html

• Raspbian kernel and initramfs

https://raspberrypi.stackexchange.com/questions/49980/raspbian-kernel-and-initramfs

• Understanding kernels on the Raspberry Pi and Raspi-LTSP

https://pi-ltsp.net/advanced/kernels.html

• Qemu-rpi-kernel

https://github.com/dhruvvyas90/qemu-rpi-kernel

• Ros tooling cross compilation

https://github.com/ros-tooling/cross_compile

• ROS2 docs cross compilation

https://index.ros.org/doc/ros2/Tutorials/Cross-compilation/#automated-cross-compilation