Finally, I couldn't use an ATtiny as it wasn't as powerful as my simulation needs it to be. I should be working on high frequencies.
The ATtiny family works with the same frequencies as the ATmega family of microcontrollers. Please define what kind of power you're missing.
So I will end up developping some bit banging I2C slave driver for Arduino or other since it will be hardware independant.
I see much more risks that this solution isn't powerful enough than using an ATtiny.
Can anyone tell me from where to start and if there are some examples or samples to begin with? I found only bit banging drivers for masters or for slaves written in asm.. I should write sth in C.
Some posts ago I gave you points to start with. You won't find finished code, you'll only find code that shows you how to use the hardware features you will need.