Remote update EPCS file format?(rpd or rbf)

Hmmm not sure I ever found a definition, which is why I had to find out the hard way that the bits are in reverse order with respect to the way the serial flash is programmed. But viewing with a hex editor, it just seems to be what it's name suggests: a binary config file (compressed if you have compression enabled). There are some bytes at the top that never change - some kind of header.