I did a little work late last night on some cheap 17mm boost drivers I had around here. I was able to add dimming and modes using the attiny13a by bootstrapping off of the output to power the attiny13a. Dimming is accomplished by disconnecting LED- with an external FET. This works with the tiny little integrated IC boost converters, but with a bigger converter with more amps you would want to PWM bias the feedback instead. This one seems to pull about 2.1A out of an Eneloop. I didn't check the output but at 2.1A in I doubt it is at 1A out. It was simply a proof-of-concept--now to get to work with a better IC.