Let's say I'm developing a control system for a UAV and I've decided to use Linux with RTAI in the vehicle. I have a real-time task which does the actual actuation of the flight surfaces and it controls the hardware (motors) through GPIO pins. The RT task is talking to Linux through a fifo (which Linux processes see as a block device) and Linux has a device driver for a wireless radio data transceiver to talk to the base station.
The problem I see is that data being fed to the RT task is non-deterministic since the data comes from Linux. This implies that to get proper hard Real Time response one would have to write a RT device driver for the wireless data transceier as well. In other words, the use of Linux wouldn't really help very much. Even in a factory setting where the UI updates are being handled by Linux there would still need to be a RT Ethernet driver to talk to other factory floor devices for the same reason as illustrated above.
So is RT Linux actually a good choice?