> trivial if you already know a language like C
The few times I've been stuck writing code for a platform without access to a compiler, I just wrote it in pseudo-C then hand-compiled it. Once I got comfortable I could "compile" on full mental autopilot, checked out and watching TV at the same time. But it's horribly dull work, like doing arithmetic by hand.
The actual mechanics of how to write a program in assembly are trivial if you already know a language like C.