PRB: Control Message Fails when Trying Dynamic VxDs as Static (141231)


The information in this article applies to:

  • Microsoft Win32 Device Driver Kit (DDK) Windows 95
This article was previously published under Q141231

SYMPTOMS

While developing a new dynamic VxD for Windows 95, developers sometimes put the VxD into the System.ini files's [386Enh] section as a "device=" line to test initialization or other basic function. During early testing, the .inf might not be generated or the loading application may not be working yet, so this seems a good way to temporarily test some functions. Yet, the initialization routines are never called.

CAUSE

This is due to the fact that the control messages that VMM sends out for static and dynamic VxDs are not the same. Refer to the library compact disc or Vmm.doc from the DDK. To summarize (from VMM.DOC):

Static messages

Device_Init         Virtual devices initializing (interrupts enabled).
Init_Complete       All virtual devices have initialized.
Sys_Critical_Exit   System is terminating (interrupt disabled).
Sys_Critical_Init   Virtual devices initializing (interrupts disabled).
System_Exit         System is terminating (interrupts enabled).

Dynamic messages

Sys_Dynamic_Device_Exit   Dynamic VxD being unloaded (directed).
Sys_Dynamic_Device_Init   Dynamic VxD being loaded (directed).

RESOLUTION

If you are planning to switch back and forth, you may want to include both types of messages in your control message procedure, for example: 
   Control_Dispatch SYS_DYNAMIC_DEVICE_INIT, My_Init
   Control_Dispatch DEVICE_INIT, My_Init

Also, don't forget to finally remove the System.ini "device" line when your dynamic loading is working.

STATUS

This behavior is by design.

REFERENCES

Windows 95 DDK
MSDN Library Compact Disc October 1995
Modification Type:MinorLast Reviewed:5/24/2004
Keywords:KB141231
©2004 Microsoft Corporation. All rights reserved.