Hi folks,

I'm currently developing a sensor framework based on the TWI bus and I 
use ATtiny85's as sensor nodes.
I want them to be able to communicate as TWI master, therefore I wanted 
to implement the USI in TWI mode with Timer0 as clock.

So my questions are:
1. Do I have to use OCR0A or OCR0A?
2. When using Timer0, do I have to generate the clock manually or is it 
done by the HW?
3. For bus arbitration I would need to detect if the bus is in use. Is 
there a efficient way the detect stop conditions?

Unfortunately not even AVR believes in the USI interface and the whole 
application notes depend on polling and the ATtiny85's datasheet is very 
vague on this topic.

Thanks in advance.