How is the rumble intensity of the GC controllers being controlled?

[ManuelVo]

This could very well be the case. Unfortunately I don't have much knowledge about the inner workings of a GameCube at all. I'm trying to improve GC Controller Driver Support under Linux and am kinda hoping to find people here that know enough about the GC to give me a definitive answer to what's going on. If games really do rumble intensity control in software, maybe I could emulate a similar behavior in the driver to enable intensity control there. But before going that route I'd like to confirm that there really is no built-in way to do intensity control.