Building a Virtual Device

Building a Virtual Device

1 Create the virtual device source files and assemble the sources using MASM.EXE, the 32-bit flat-model assembler.

2 Create a module definition file (.DEF) and link the object files using LINK.EXE, the 32-bit flat model linker. By convention, the resulting executable file should have the same filename as the virtual device, but with the filename extension .VXD.

3 Create a debugging symbol file for the executable file using MAPSYM.EXE.

A virtual device is not compatible with Windows dynamic-link libraries. Windows-based applications cannot load and use virtual devices directly. However, Win32-based applications can use the CreateFile and DeviceIoControl functions to load and interact with dynamically-loadable VxDs.

The module definition file for a virtual device has the following form:

LIBRARY VSAMPLED
DESCRIPTION 'VSAMPLED Device (Version 4.0)'
EXETYPE DEV386
SEGMENTS

_LTEXT PRELOAD NONDISCARDABLE

_LDATA PRELOAD NONDISCARDABLE

_ITEXT CLASS 'ICODE' DISCARDABLE

_IDATA CLASS 'ICODE' DISCARDABLE

_TEXT CLASS 'PCODE' NONDISCARDABLE

_DATA CLASS 'PCODE' NONDISCARDABLE
EXPORTS

VSAMPLED_DDB @1

The LIBRARY statement must specify the name of the virtual device, as given in the device description block (DBB) and the EXPORTS statement must specify the name of the DBB. In all cases, the export ordinal for the DDB is 1.