Piccolo OS is a multitasking OS designed for Raspberry Pi Pico, focusing on teaching. It lacks several features like per-task memory, multicore support, a file system, among others. The author kindly dismisses C/C++ pedants and welcomes contributions from like-minded individuals. The OS uses a round-robin task selection algorithm, switching between the kernel and user tasks via an interrupt. The Cortex-M0+ processor operates in Thread or Handler mode, utilizing Main and Process Stack Pointers. Context switching involves saving the current state onto the appropriate stack. Overall, Piccolo OS provides a simple, educational approach to understanding co-operative multitasking systems using Arm Cortex-M0+.
https://github.com/garyexplains/piccolo_os_v1