## Input/Output Device Driver Reference

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### Communications from Physical Device Driver to Virtual Device Driver

The physical device driver (PDD) uses touch data packets to communicate with the virtual device driver (VDD). While the virtual mouse device driver can receive mouse data from the Presentation Manager that is correctly adjusted for DOS window sizes and positions, the same is not true for touch data. Normally, therefore, a DOS session receives touch data only when it is running full screen (that is, a non-PM foreground session). In a PM session, all touch data is used to form emulated mouse packets and is reported to the physical mouse device driver. The virtual mouse device driver then receives the emulated mouse data by way of the normal PM route (or physical driver route if exclusive mouse access in On).

The exclusive touch access DOS property, however, permits a DOS window to receive all touch data when running in a PM session. The DOS window must be running maximized (except for text-mode applications where maximizing a window does not cover the full screen) in order to run without modification . Otherwise, the application has to perform the coordinate conversions itself, an impossible task for a DOS program because it has no knowledge of or access to window position and size information.

The VDD entry point is passed to the PDD when the VDD calls VDHOpenPDD with the 16:16 address of VTEventProc as a parameter, as shown in the following code: