See [UNMAINTAINED] Canon 5D Classic Firmware ** Beta 4 **. @Claes linked to it above but I would like to share it again and note that the research and discussion is still ongoing. It is just that 5Dc is quite different from the other cameras. They may also need more hardware donations if you have a camera to spare; perhaps if a1ex has one, we could move that thread out of the unmaintained status.