There are a few options.
Depending on the interface hardware you want to use, the software will change.
Luckily, we have example projects on our Wiki that show you how to implement each of these options.
The wiki page containing example projects is here: http://wiki.analog.com/resources/tools-software/sigmastudio/tutorials
The top level wiki is here: http://wiki.analog.com/resources/tools-software/sigmastudio
Links to the individual project files (in zip archive format) are here:
(These particular projects are designed to work with the ADAU1701/ADAU1702/ADAU1401A SigmaDSPs, but the same design techniques can be applied to other SigmaDSPs as well)
For information about hardware design for GPIO controls, refer to this application note: