anybody try to modify nios II code?

Actually the changes are not as big as you might think. It was more of a jump in terms of the tools provided to you and the core hardware itself (there is a pretty good chance that the software you wrote for NIOS I still works with NIOS II as is). They also provided a legacy upgrade path if you would like to use it instead (you can't use the "f" core doing that though because it would be difficult to support the data cache changes).

You are use to using the excalibur.h file to get at your system parameteres, now it's a system.h file that's created when you compile your system project.

Your system project is something that would be new to you. Basically the system project handles all the driver code for the IP cores, and it gives you the interface to talk to them (so you don't need to be directly talking to memory, you use function calls now).

I highly recommend using their new IDE that comes with the NIOS II, because it's not only an editor, but you can use it for debug, and communication between the NIOS II and your host PC/System.

Here's the link to the NIOS II documentation: http://www.altera.com/literature/lit-nio2.jsp (http://www.altera.com/literature/lit-nio2.jsp)

If you want to just be familar with the software aspect then I would jump directly to the software tutorial. If not then I would look into the big document at the top which covers pretty much everything you would need to know about the core, then follow that up with the hardware and software tutorials.

If you have further questions leave your reply and either myself or any of the others here would give you a hand.

Good-luck