The full protocol is described in the Hyperdeck Manual Page 54.
Can't quote from the new manuals anymore.. As they have copy protection on there PDF files...
But here a quote from a old manual:
Blackmagic HyperDeck Ethernet Protocol
Version 1.8
The Blackmagic HyperDeck Ethernet Protocol is a text based protocol accessed by connecting
to TCP port 9993 on HyperDeck Studio models that have a built in Ethernet connection. If you
are a software developer you can use the protocol to construct devices that integrate with our
products. Here at Blackmagic Design our approach is to open up our protocols and we eagerly
look forward to seeing what you come up with!