Hi
I suppose that you want to do this in a Nios System. In that case you need to create a SOPC Custom Component (IP-Core). Then it will require some time.
First read carefully the Avalon specification so you can understand how to deal with the Avalon Fabric which interact with the Master/Slave ports of your IP.
http://www.altera.com/literature/manual/mnl_avalon_spec.pdf (
http://www.altera.com/literature/manual/mnl_avalon_spec.pdf)
Second, exercise the tutorial "Design Example Checksum Master" in "Quartus II Version 7.2 Handbook Volume 4: SOPC Builder"
http://www.altera.com/literature/hb/qts/qts_qii5v4.pdf (
http://www.altera.com/literature/hb/qts/qts_qii5v4.pdf)
At this point you should understand how to do a simple SOPC component. Then, you can modify the checsum component to introduce the I2C module you have and to add slave registers that allow you to control the I2C module commands via Nios software (C++).
Well, this is the idea. Good Luck!
Regards
Byron
