Since I just discovered that I can replace Ubunto with lighter-weight Raspbian on old 32-bit PCs, I thought it would be a good time to quickly jot down some notes about going the other way: replacing Raspbian with Ubuntu on Raspberry Pi.
When I started building Sawppy in early 2018, I was already thinking ahead to turning Sawppy from a remote-controlled toy to an autonomous robot. Which meant a quick survey to the state of ROS. At the time, ROS Kinetic was the latest LTS release, targeted for Ubuntu 16.
Unfortunately the official release of Ubuntu 16 did not include an
armhf build suitable for running on a Raspberry Pi. Some people would build their own ROS from source code to make it run on Raspbian, I took one attempt and the build errors took more time to understand and resolve than I wanted to spend. I then chose the less difficult path of finding a derived released of Ubuntu 16 that ran on the platform: Ubuntu Mate 16. An afternoon’s worth of testing verified basic ROS Kinetic capability, and I set it aside for revisiting later.
Later on in 2018, Ubuntu 18 was released, followed by ROS Melodic matching that platform. By then support for running Debian (& deriviatives) on armhf had migrated to Ubuntu, and they released both the snap-based Ubuntu Core and Ubuntu ‘classic’ for Raspberry Pi. These are minimalist server images, but desktop UI components can be installed if needed. Information to do so can be found on Ubuntu wiki but obviously UI is not a priority when I’m looking at robot brains. Besides, if I wanted an UI, Ubuntu Mate 18 is still available as well. For Ubuntu 20 released this year, the same choices continue to be offered, which should match well with ROS Noetic.
I don’t know how relevant this is yet for ROS on a Raspberry Pi, but I noticed not only are 32-bit
armhf binaries available, so are 64-bit
arm64 binaries. Raspberry Pi 3 and 4 have CPU capable of running
arm64 code, but Raspbian has remained 32-bit for compatibility with existing Pi software and with low-end devices like the Raspberry Pi Zero incapable of
arm64. More than just an ability to address more memory, moving to
arm64 instruction set was also a chance to break from some inconvenient bits of architectural legacy which in turn allowed better
arm64 performance. Though the performances increase are minor as applied to a Raspberry Pi, ROS releases include precompiled
arm64 binaries so the biggest barrier to entry has already been removed and might be worth a look.