## MMPM/2 Device Driver Reference

[prev][next][parent][TOC]

### Inter-Device Driver Communication (IDC) Interface

Virtual device drivers (VDDs) communicate with physical device drivers ( PDDs) through the inter-device driver communication (IDC) interface provided with the OS/2 operating system. The drivers exchange the address of an entry point and call each other through the exchanged addresses. A VDD communicates with a PDD directly through a callable 16:32 interface or by using the Virtual DevHlp services that map to File System APIs.

Physical device drivers and virtual device drivers use the following OS/2 DevHlp functions to establish inter-device driver communication (IDC).

RegisterPDD This function is called by the PDD during initialization to advertise a 16:16 entry point for VDD-PDD communication. The PDD provides a textual name, which the VDD must supply during its initialization.

VDHOpenPDD This function gets the address of the routine in a physical device driver that the virtual device driver uses to communicate with the physical device driver. The physical device driver's device must have previously registered its name and entry point using the DevHlp service, RegisterPDD. If the function is successful, it returns a pointer to the physical device driver IDC entry point.