Patch mechanism for allowing dynamic modifications of the behavior of a state machine

摘要

A patch mechanism for dynamic modification of the behavior of a state machine without interfering with normal operation of the state machine when modification is not required. The patch mechanism uses a programmable logic array for storing a modified transition and a modified output transition for an individual state of the state machine which is to be modified. A pair of multiplexer having inputs coupled to the state machine and inputs coupled to the programmable logic array are used for allowing the state machine to select either the current transition and the current output transition both defined by the state machine, or a modified transition and a modified output transition if a modification of the present state is required. A logic circuit coupled to the state machine and to both multiplexers will signal both multiplexers when it is valid to modify the present state to the modified transition and the modified output transition.