Reconfiguring one-time programmable FPGAs

Field-programmable gate arrays can suffer from a variety of faults, ranging from wire anomalies and defects to inoperative programmable connections. The solution to these faults depends on whether or not we are dealing with a reprogrammable FPGA or a one time programmable (OTP) FPGA. To correct faults, developers can reconfigure FPGAs such as those made by Xilinx and Altera by reprogramming. These devices can be programmed many times, for different designs and applications. Correcting faults in OTP FPGAs, such as those made by Actel is more difficult. For one thing, OTP FPGAs are based on antifuses. With an antifuse, the FPGAs configuration information has an initial (default) value that can be changed, but once changed cannot be restored. Therefore, the procedures to bypass faulty cells or faulty routing in an OTP FPGA must meet more stringent requirements than for reprogrammable FPGAs. The “Reconfiguration Approaches” sidebar describes two methods other researchers have tried. This article describes our approach to reconfiguring OTP FPGAs. We explain how we determine if reconfiguration is feasible, the algorithms we used, and the results of our experiments on a generic OTP FPGA model and a generic detail router