Various approaches for generating input data for simulating a circuit design are disclosed. In one approach, a test generator program is generated from a main program that uses a test generator class library. The test generator class library includes a software driver class corresponding to the hardware driver, and the software driver class includes a storage class corresponding to each memory within the hardware driver, a first set including at least one method for writing function codes to a first object of the storage class, and a second set including at least one method for writing data to a second object of the storage class. Function codes are written to the first object of the storage class in response to a call by the test generator program to a method in the first set. Data of a first type is written to the second object of the storage class in response to a call by the test generator program to a method in the second set, wherein the data of the first type is data to be provided by the driver as input to the simulated circuit design.