What's on the UDRC board? How is GMSK frames decoded?


I'm looking closely at the UDRC board to add d-star to a yeasu repeater. 

What is on the board to make this work?  Is there a GMSK decoder on the board? or is this supposed to be done in software?  The colloquial description I have heard of the board, is that it's just a nicely packaged "sound card".

Thanks for the clarification!

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