Warning
This project is a proof of concept and is not intended for production use.
This is an exploration of a system that allows for dynamic loading of "cross-platform" applications on any risc-v system. This is intended to emulate the behavior of a traditional operating system, but with a much simpler design.
For a long time, I have been thinking about writing a framework for creating portable apps for micro controllers. Most projects resort to integrating a "light weight" interpreter like MicroPython, lua or berry. This has never sat right with me due to the horrible efficiency. Not just in execution speed, but also FLASH/RAM usage. I wanted a system closer to a real operating system and I think I got pretty close with this project.
The "app" is compiled as position independent code. All of the app's symbols are accessed though a GOT (Global Offset Table). At load time, the loader will load the app into memory and resolve the GOT. After compilation, the app is packaged into a simple binary format with a header that can be used by the loader to resolve the GOT.
The entry point is always at the start of .text section.
All "kernel" functions are passed though a sys struct pointer which implements a simple jump table. This is always placed as the first item in .data section of the app.
The example kernel shows how FreeRTOS can be used to easily run the multiple apps concurrently.