That's a key point, Altera and Xilinx may well have decided to keep some of their inventions secret, banking on being able to keep them secret, In which case a

That's a key point, Altera and Xilinx may well have decided to keep some of their inventions secret, banking on being able to keep them secret, In which case a patent may do them little good. And there is no 7-year date of expiry on secrets.