Microsoft KB Archive/244771

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INFO: The VMD_Set_Mouse_Data Function

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Q244771

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The information in this article applies to:


 * Microsoft Windows 98 Driver Development Kit (DDK)

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SUMMARY
Virtual device drivers (VxDs) that call the VMD_Set_Mouse_Data function should only specify a MouseType of PS/2 when the Auxiliary Device is present on the system and virtualized by the Virtual Auxiliary Device (VAD) driver, which is usually integrated into the Virtual Keyboard Driver (VKD).

If a VxD calls the VMD_Set_Mouse_Data function with a MouseType of PS/2, VMOUSE will overwrite its VAD_Exists data field with a value of 1, meaning that it is functioning as if VAD is present. However, if VAD support is not currently loaded, a critical internal VAD data field will remain uninitialized, resulting in problem behavior, including corruption of DOS-box property settings. Specifically, the "Always suspend" check box on the MS-DOS Prompt Properties page may be affected.

Drivers for non-PS/2 mice (for example, Universal Serial Bus [USB] Human Interface Device [HID] mice) that call the VMD_Set_Mouse_Data function should not specify a MouseType of PS/2 in order to avoid this problem behavior.

MORE INFORMATION
The VMD_Set_Mouse_Data function allows VxDs to register mouse information with the VMD (Virtual Mouse Device). The VMD provides this mouse information to applications and drivers that make int 33h calls. The VMD maintains this information for only one mouse; a second call to the VMD_Set_Mouse_Data function will overwrite any existing mouse data.