[hwh]

@TheOtherCliff   The firmware in the atmel based ones was written by http://www.rcgroups.com/forums/member.php?u=393936 it's under Naza GPS module alternative (using APM 2.6 GPS/compass combo).  Unfortunately he didn't release the source code to his adapter but his posts document everything known about the protocol.

His page also has the protocol decoder he wrote.

[TheOtherCliff]

I recall reading about a protocol description and source for a library for the DJI protocol.  That is probably where I will start.