I've been busy writing the communication protocols between the Ground Station and Autopilot. I thought some people might be interested and possibly make use of the approach I've taken. It's all done in binary with discrete packets and makes use of DMA and Interrupts to use as little processor time as possible.
Asynchronous operation is achieved by the use of two FIFO queues and double buffered DMA channels for each radio. There is a lot of detail that will make the diagram above make a bit more sense.
Full article at: http://www.projectandromeda.com.au/blog