hardware or software for critical control systems

Faceless

I think that the true reason on why software approach is much less reliable lies in one simple fact: there's always a some kind of hardware abstraction layer present within software system and way we design this layer greatly affect formal verification process of any system going to be formally verified & certified as SIL2 or above.
I.e. we need to make this layer as thin and transparent as possible.
IMHO one of solutions here might be a real-time Java processors.
Here is a link on commercial product describing features I consider interesting http://www.aonix.com/pdf/raven-web.pdf

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Peoples risk perception is almost always focused on the most dramatic rather than the most probable. (c) Gordon Smith