[ironic_monkey]

abrombo, it's mostly monkey see, monkey do.

start out with looking at the source of one of them, e.g. https://github.com/kodi-adsp/adsp.basic
there used to be an empty template but it seems the repository is just that atm - empty.
if you are not used to add-ons in general, there are some general stuff you have to get the grasp of, feel free to ask specific questions.

the interfaces are mostly doxy'd;
https://github.com/xbmc/xbmc/blob/master...adsp_dll.h
https://github.com/xbmc/xbmc/blob/master...sp_types.h
https://github.com/xbmc/xbmc/blob/master...ODI_adsp.h