Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

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xor     bx, bx
mov     es, bx          ; es:bx contains 0000h:0000h
 
mov     cx, 0000h
mov     dx, [Flags]     ; bit 0 clear if 386 enhanced mode,
                        ; set if standard mode
 
mov     di, [Ver_Num]   ; major/minor version numbers
                        ; (in high/low bytes)
 
xor     si, si
mov     ds, si          ; ds:si contains 0000h:0000h
 
mov     ax, 1605h       ; Windows Initialization Notification
int     2fh             ; multiplex interrupt
 
cmp     cx, 0
jne     no_initialize   ; if nonzero, don't continue initialization
 
 
 
Windows Initialization Notification (Interrupt 2Fh Function 1605h) notifies
MS-DOS device drivers and TSRs that standard- or 386 enhanced-mode Windows
is starting. Windows calls this function as it starts allowing MS-DOS device
drivers and TSRs that monitor Interrupt 2Fh the opportunity to prepare for
running in the Windows environment.
 
Parameter  Description
────────────────────────────────────────────────────────────────────────────
 
Flags      Specifies whether standard- or 386 enhanced-mode Windows is
           initializing. 386 enhanced-mode Windows sets bit 0 to 0;
           standard-mode Windows sets bit 0 to 1. Only bit 0 is used; all
           other bits reserved and undefined.
 
Ver_Num    Specifies the version number of Windows. The major version number
           is in the high-order byte, the minor version number in low-order
           byte.
 
Return Value
 
The return value is 0 in the CX register if all MS-DOS device drivers and
TSRs monitoring Interrupt 2Fh can run in the Windows environment, and
Windows can proceed with initialization. Otherwise, the CX register is
nonzero and Windows must terminate.
 
Comments
 
Any MS-DOS device driver or TSR that either cannot run in the Windows
environment, or must adapt its operation when in the Windows environment
should add itself to the Interrupt 2Fh chain and watch for this function.
 
If the device driver or TSR cannot run in the Windows environment, it should
set the CX register to a nonzero value, display a message informing the user
of its incompatibility with Windows, and return. Windows does not print a
message of its own. Instead, it calls Windows Termination Notification
(Interrupt 2Fh Function 1606h) and returns to MS-DOS.
 
If the device driver or TSR can run in the Windows environment, it should do
the following:
 
1  Call the next device driver or TSR in the Interrupt 2Fh chain to allow
   all device drivers and TSRs in the chain an opportunity to respond to
   this function.
 
2  Upon return from the interrupt chain, carry out the following actions:
 
   ♦  Free any extended memory. The device driver or TSR takes this action
      only if it has previously allocated extended memory using the Extended
      Memory Specification (XMS) interface.
 
   ♦  Switch the processor to real mode, or set the DS:SI register pair to
      the address of an Enable/Disable Virtual 8086 Mode callback function.
      The device driver or TSR takes this action only if it has previously
      switched the processor to virtual 8086 mode. If standard-mode Windows
      is starting, the device driver or TSR must switch the processor to
      real mode──the callback function is permitted for 386 enhanced-mode
      Windows only.
 
   ♦  Initialize a Win386_Startup_Info_Struc structure, and copy the address
      of the structure to the ES:BX register pair. The device driver or TSR
      carries out this action only if 386 enhanced-mode Windows is
      starting.
 
3  Return (using the iret instruction) but without changing the CX
   register.
 
For more information about these procedures, see the following "Comments"
section.
 
The device driver or TSR must preserve all registers and restore the
original values before returning. The only exceptions to this rule are
changes made to the BX, CX, DS, ES, and SI registers as a result of
following the previous procedure.
 
Enable/Disable Virtual 8086 Mode CallBack Function
 
Some device drivers and TSRs, such as expanded memory emulators, switch the
processor to virtual 8086 mode. Because 386 enhanced-mode Windows cannot
start successfully while the processor is in this mode, any device driver or
TSR that switches to virtual 8086 mode must either switch back to real mode
or supply the address of a callback function that can switch between real
and virtual 8086 modes.
 
Windows uses the callback function to disable virtual 8086 mode before
Windows itself enters protected mode. Windows calls the callback function
again to enable virtual 8086 mode after Windows exits protected mode.
Windows calls the callback function using a far call instruction, and it
specifies which action to take by setting the AX register to 0 or 1.
 
To disable virtual 8086 mode, Windows sets the AX register to 0, disables
interrupts, and calls the callback function. The function should switch the
processor to real mode, clear the carry flag to indicate success, and
return. If an error occurs, the function sets the carry flag and returns.
Windows checks the carry flag and terminates if it is set.
 
To enable virtual 8086 mode, Windows set the AX register to 1, disables
interrupts, and calls the callback function. The function should switch the
processor to virtual 8086 mode, clear the carry flag, and return. If an
error occurs, the function sets the carry flag and returns. However, Windows
ignores the carry flag, so if an error occurs no action is taken and the
processor is left in real mode.
 
Whether an error occurs when enabling or disabling virtual 8086 mode, it is
up to the callback function to display any error message to the user. Also,
the callback function must not enable interrupts unless an error occurs, and
the function sets the carry flag.
 
A device driver or TSR supplies a callback function by copying the address
of the function to the DS:SI register pair when it processes the Windows
Initialization Notification (Interrupt 2Fh Function 1605h). Windows permits
only one callback function, so the device driver or TSR should first check
to make sure that the DS and SI registers are both zero. If they are
nonzero, the device driver or TSR should set the CX register to a nonzero
value and return, directing Windows to terminate without starting.
 
Initializing a Win386_Startup_Info_Struc Structure
 
An MS-DOS device driver or TSR initializes a Win386_Startup_Info_Struc
structure to direct 386 enhanced-mode Windows to load the virtual device and
to reserve the instance data the device driver or TSR needs to operate in
the Windows environment. The device driver or TSR is also responsible for
establishing a chain of startup structures by copying the contents of the
ES:BX register pair to the Next_Dev_Ptr member. It is assumed that any other
device driver or TSR in the Interrupt 2Fh chain will have set the ES:BX
register pair to the address of its own startup structure prior to
returning.
 
Any device driver or TSR can use a Windows virtual device to help support
its operation in the 386 enhanced-mode Windows environment. To specify a
virtual device, the device driver or TSR sets the SIS_Virt_Dev_File_Ptr
member to the address of the virtual device's filename. The device file is
assumed to be in the Windows SYSTEM directory. The device driver or TSR can
also set the SIS_Reference_Data member to specify additional data to be
passed to the virtual device when loaded.
 
Any device driver or TSR can reserve instance data for itself. Instance data
is one or more blocks of memory used by the device or TSR, and managed by
Windows. For device drivers or TSRs loaded before 386 enhanced-mode Windows
starts, reserving instance data allows the device driver or TSR to keep
separate data for each virtual machine. Whenever Windows switches virtual
machines, it saves the previous VMs instance data and loads the current VMs
instance data. If a device driver or TSR does not specify instance data, the
same data is used for all virtual machines.
 
A device driver or TSR reserves instance data by appending an array of
Instance_Item_Struc structures to the Win386_Startup_Info_Struc structure.
The last structure in the array must be set to zero. Each
Instance_Item_Struc structure specifies the starting address and size (in
bytes) of an instance data block.
 
The device driver or TSR must copy the address of its startup structure to
the ES:BX register pair before returning.
 
See Also
 
Win386_Startup_Info_Struc, Instance_Item_Struc
 
 
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