I have undertaken many different projects through the years, one area which I have not really explored is Operating System development. When I started developing software on 8 bit computers, the closest you came to an OS was a ‘monitor’ or perhaps a ‘Master Control Program’ for those old enough to remember Tron.

I have started tinkering with a 64 bit operating system for Raspberry Pi based computers. Given how powerful those small single board computers have become, they make a great platform for OS experimentation.

My goals for this project are four-fold:

1. Get back to ‘bare metal basics’ for a while
2. Provide a platform for experimentation with different approaches to OS architecture
3. Explore the advantages and disadvantages of C++ for OS development
4. Provide a collection of tutorials and working code for others to learn from

C++ for OS Development

There is a definite bias against C++ for bare metal programming, though increasingly there are bare metal projects utilizing C++. In the Raspberry Pi ecosystem, the Circle – C++ Bare Metal Environment for Raspberry Pi is perhaps the best and most useful example. It is a remarkable system.

Prior to C++ 11, I probably would not have considered this but now at C++ 20 and beyond the language system is both rich enough and flexible enough to span from bare metal up to the highest application layer development. At the time of writing, this project is built with C++ 20.

Part of my goal is to create a single image which runs across multiple RPI versions and makes obvious the points at which board specific code is required. My approach is to create interfaces using classes and abstract virtual functions which, yes adds a bit of overhead but anymore it is minimal. The optimizations available in modern compilers and increased clarity associated with C++ code may help close the performance gap between C and C++.

I am not particularly concerned about size at present. On systems with gigabytes of RAM, the difference between a 64k kernel and a 128k kernel is negligible. Honestly the kernel size is going to be much more tightly correlated to the OS architecture than the implementation language or optimizations. A monolithic kernel containing lots of services will be big whereas a microkernel with most services running in user space will be much smaller. These days though, I tend to favor speed over size.