In this paper we propose a generic frame for the implementation of a dual-core processor with two modes of operation. One is the safety mode that allows to run the two cores in lock step in a classical master/checker fashion. A clock delay of 1.5 clock cycles between master and checker establishes the temporal redundancy to minimize the potential for common mode faults. The second operation mode allows a parallel execution of different instruction streams on the two cores in a multiprocessor fashion. The possibility to dynamically switch between the two modes allows for an efficient utilization of the duplicated core. We propose an implementation of such a generic frame that can be applied in conjunction with virtually any standard processor core. Also we perform a systematic failure analysis for the safety mode and the mode switching procedure. Experimental fault injection confirms that our reconfigurable architecture indeed provides the same fail safe properties as the classical master/checker architecture.