anything complex in assembly (I wrote the control logic and interfaces in C), but having your hands all the way down in the registers and bits of fundamental operations in order to make them just as efficient and fast as possible was actually kind of fun.

That was early in my career, and I haven't touched a low level language in decades now. (But having the understanding of what's going on under the hood has been helpful, even with very high level languages.)

And, yes, I'll save everyone the time and post this here: