This might not be an answer you want, but I wrote code runs on Raspberry Pi Pico that doesn't use OS.
* Example code takes a GPIO input using IRQ handler: <https://github.com/demotomohiro/picosdk4nim/blob/main/examples/gpioInIRQ.nim> * Example code to copy string using DMA: <https://github.com/demotomohiro/picosdk4nim/blob/main/examples/dma.nim> PicoSDK4Nim wraps Raspberry Pi Pico SDK and these example code calls C functions in the SDK. I have never tried to directly access memory mapped hardware registers on Pico. But I think Nim can do so because Nim has [Volatile pragma](https://nim-lang.org/docs/manual.html#implementation-specific-pragmas-volatile-pragma) and probably can do the same things as C functions in this header file: <https://github.com/raspberrypi/pico-sdk/blob/master/src/rp2_common/hardware_base/include/hardware/address_mapped.h> And Nim has [Assembler statement](https://nim-lang.org/docs/manual.html#statements-and-expressions-assembler-statement) in case you need to use CPU instructions C compiler doesn't emit. Raspberry Pi Pico has good documentations: * <https://www.raspberrypi.com/documentation/microcontrollers/> * <https://www.raspberrypi.com/documentation/pico-sdk/> * <https://github.com/raspberrypi/pico-sdk> * <https://github.com/raspberrypi/pico-examples>
