In practice such a hard realtime guarantee can only be met by a devices like an FPGA.
There have always been fully deterministic CPUs around for that purpose. The simpler the system, the better; just hook a Forth chip to a memory without caches and you're set.
No, but I don't see any flaw in that design. Indeed, it seems like the case of Hoare's "obviously no deficiencies" in a system design.
I believe that the GreenArrays people, setting aside the $450 dev board, also had some notes on making cheap breadboards with their chips or something like that. I don't have a link handy, though. ;/
There have always been fully deterministic CPUs around for that purpose. The simpler the system, the better; just hook a Forth chip to a memory without caches and you're set.