  Evolvable hardware combines the powerful search capability of evolutionary
algorithms with the flexibility of reprogrammable devices, thereby providing a
natural framework for reconfiguration. This framework has generated an interest
in using evolvable hardware for fault-tolerant systems because reconfiguration
can effectively deal with hardware faults whenever it is impossible to provide
spares. But systems cannot tolerate faults indefinitely, which means
reconfiguration does have a deadline. The focus of previous evolvable hardware
research relating to fault-tolerance has been primarily restricted to restoring
functionality, with no real consideration of time constraints. In this paper we
are concerned with evolvable hardware performing reconfiguration under deadline
constraints. In particular, we investigate reconfigurable hardware that
undergoes intrinsic evolution. We show that fault recovery done by intrinsic
reconfiguration has some restrictions, which designers cannot ignore.
