Everything by ear and memory, never had a need to write anything down except when I had to rehearse many unfamiliar tracks in a short space of time, in which case I would make up my own primitive method of drum notation as I’d never learnt the proper way. I think there was some sheet music printed in Japan way back, after the second album maybe. Try listening and having a go, it’s much more fun. It’s not like other instruments whereby you need to learn chord shapes, you just need to play the beats as you hear them, and each element of the kit is pretty easy to determine.