There's nothing terribly difficult to writing specific routines in asm. It's kinda fun, actually. Assembly _in the large_ is hard, just because you need to be next-level organized to keep things from being a mess.
I find it rather easy as long as you don’t have to interact with the OS. That’s where it becomes messy, with inflexible data structures and convoluted arguments in ABIs designed to be used from higher level languages.
If you are doing really low level stuff, sometimes it’s worth rolling out your own little RTOS with just the bits and pieces you need.
Not that long ago, I realised most 8-bit (and MS-DOS) computer games had their own RTOS woven into the game code, with multi-tasking, hardware management, IO, and so on.
