A programmed computer searches for functional defects in a description of a circuit
undergoing functional verification in the following manner. The programmed computer
simulates the functional behavior of the circuit in response to a test vector,
automatically restores the state of the simulation without causing the simulation
to pass through a reset state, and then simulates the functional behavior of the
circuit in response to another test vector. A predetermined rule can be used to
identify test vectors to be simulated, and the predetermined rule can depend upon
a measure of functional verification, including the number of times during simulation
when a first state transition is performed by a first controller at the same time
as a second state transition is performed by a second controller. During simulation
of the test vectors, manually generated tests or automatically generated checkers
can monitor portions of the circuit for defective behavior.
