If your card uses one of the standard codecs (listed in the Supported Codecs appendix), the amount of work you have to do is reduced.
The benefit of using standardized codecs is that you just have to write a few access functions, typically the ones that read and write the codec registers.
Before we can write these functions, we need to get some basic requirements of the driver out of the way. We need a build environment to build this code as a DLL and we need to provide a standard entry point for io-audio to call to initialize the chip.
The easiest way to do this is to copy one of the existing driver directories (/audio/src/hardware/deva/*) in the DDK to a directory named for your card or chip type. The best code to copy is either the template driver or the Sound Blaster (sb), depending on your answers to the questions in the Evaluating Your Card chapter. After copying the directory, you should rename the C, header, and use files to something more descriptive of your chip. After doing this, make sure the code still compiles before proceeding.