Just out of curiousity, did you look at the real-time HAL included with LinuxCNC at all? There have been attempts to make that code into a dedicated PLC system now and again.
What real time extensions did you use with the Raspbian kernel?
What real time extensions did you use with the Raspbian kernel?
https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-sta...
That patch set is slowly being upstreamed into the mainline kernel. We regularly encounter incompatibilities with drivers for the Raspberry Pi SoC and upstream our fixes and feature work as well, e.g.:
https://git.kernel.org/linus/f7da7782aba9
https://git.kernel.org/linus/3c7b30f704b6
I must admit I wasn't aware of LinuxCNC, thanks for the pointer. This would seem to be a really nice use case for Revolution Pi.