Bare metal programming in C99 hasn't changed in... Ever really, so that's another option if you want something less esoteric than Forth. (Though Forth is a lot

Bare metal programming in C99 hasn't changed in... Ever really, so that's another option if you want something less esoteric than Forth. (Though Forth is a lot of fun and will give you a dynamic experience that few other environments at this level of the stack can offer.)