I found there is a official OF-DPA web site that contains some good information about RYU and OF-DPA as follows:
http://ofdpa.com/
I also put my simple L2 switch RYU app for OF-DPA which I had done an example in the last year and cannot guarantee there is no error/bug. But, it is still worth referencing. Enjoy.
Here it is:
https://github.com/teyenliu/OF-DPA