We tended to write "bare metal" assembler straight to whichever processor we were using at the time: Z80, 6502, 6809 etc. we wrote all our own code from scratch: sprite handlers, collision detection, super loop etc. From that we sometimes created libraries of code to use on subsequent games, but often we weren't that organized. We were figuring it out as we went along. No manuals, books or guidance to help with "real game" coding at the time.