From Custom Instruction to Custom Peripheral

I would suggest taking a look at www.terasic.com (http://www.terasic.com) and downloading the example files for the 5mp camera module.

It is not written for a NIOS interface, but does use the ALTSHIFT_TAPS. From my limited analysis of the example, it appears to do a bayer pattern to rgb colorspace conversion in real time after reading the first 3 lines of the ccd sensor. Perhaps this could help answer some questions and guide you closer to a solution.

Be aware that I absolutely HATE the way they write their examples, as they are almost never commented, and they use fairly cryptic register and wire names, that only become clear after you analyze the code for a little while.