When the pen driver receives DRV_ENABLE, it performs system operations such as hooking interrupts, initializing hardware, and so forth. It also calls the virtual pen driver to notify it to start sending pen packet information. Note that the tablet is in its default state at this point, having been set by the virtual device driver when it was initialized.
The DRV_DISABLE message reverses the process, telling the pen driver to restore the system back to its original state. When processing this message, the pen driver calls the virtual pen driver stop sending pen packet information.
The pen driver exists in memory between the DRV_ENABLE and DRV_DISABLE messages. The driver receives these messages only once during loading and unloading.