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documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

                                                     ◄Up► ◄Next► ◄Previous►
────────────────────────────────────────────────────────────────────────────
 
include vcd.inc
 
VxDcall VCD_Virtualize_Port
 
The VCD_Virtualize_Port service virtualizes a COM port. This service allows
additional virtual devices to provide enhanced capabilities to COM port
virtualization. An example virtual device is one which buffers high speed
input data, and then simulates interrupts into the owner virtual machine, at
a slower rate, so that the virtual machine can keep up with the data without
losing input.
 
This service can only be called during processing of the Sys_Critical_Init
message.
 
Parameter  Description
────────────────────────────────────────────────────────────────────────────
 
EAX        Specifies the port number (1, 2, 3, or 4).
 
EBX        Specifies the operation flags. It is 00000001h if the IRQ is
           sharable. All other values are reserved.
 
ECX        Specifies the number of extra bytes needed in the VCD_COM_Struc
           structure.
 
EDX        Specifies the number of extra bytes needed in the VCD_CB_Struc
           structure.
 
ESI        Points to the VCD_ProcList_Struc a structure which contains a
           list of callback procedures. The VCD saves the pointer to this
           structure, so it must be placed in the VxD_DATA_SEG segment.
 
Return Value
 
If the carry is clear, the port can be virtualized and the EAX register
contains the COM handle which points to the COM structure having the extra
data allocated at its end.
 
Otherwise, the carry flag is set if the port is not available and the EAX
register contains one of the following values:
 
Value  Meaning
────────────────────────────────────────────────────────────────────────────
0      Port does not exist
 
1      Port already virtualized
 
Comments
 
Callback procedures are provided in the list pointed to by ESI.
 
The VPS_Control_Proc callback is called when the virtualization state
changes for a COM port. Currently the only call is for ownership changes.
 
EAX     ; VCD_Control_Set_Owner
EBX     ; virtual machine handle of new owner or 0,if virtualization
        ; handled by a different device
EDX     ; virtual machine handle of previous owner or 0
ESI     ; points to a VCD_COM_Struc
 
On entry, when the EBX register specifies a new owner, port trapping will be
enabled for all I/O ports of the COM adapter. The control procedure can
disable any I/O trapping that it desires.
 
The IRQ virtualization procedures are the same as if the virtual device
virtualized the IRQ directly using the VPICD, except that ESI points to the
VCD_COM_Struc structure on entry. See the VPICD documentation for actual
entry parameters and return values.
 
EAX     ; IRQ handle
EBX     ; virtual machine handle
ESI     ; points to a VCD_COM_Struc
 
The following callbacks have default actions, if the callback offset is set
to 0:
 
Callback              Default Action
────────────────────────────────────────────────────────────────────────────
VPS_Hw_Int_Proc       Assign an owner to the current virtual machine if not
                      owned, and request an interrupt in the owner's virtual
                      machine.
 
VPS_Virt_Int_Proc     Not virtualized.
 
VPS_EOI_Proc          Physically EOI and clear interrupt request.
 
VPS_Mask_Change_Proc  Assign the owner to the current virtual machine if not
                      owned.
 
VPS_IRET_Proc         Not virtualized.
 
The following callbacks deal with I/O for ports that have trapping enabled
while the virtualizing virtual device owns a COM port.
 
VPS_In_RxTxB
VPS_Out_RxTxB
VPS_In_IER
VPS_Out_IER
VPS_In_IIR
VPS_Out_IIR
VPS_In_LCR
VPS_Out_LCR
VPS_In_MCR
VPS_Out_MCR
VPS_In_LSR
VPS_Out_LSR
VPS_In_MSR
VPS_Out_MSR
 
These callbacks have the following parameters:
 
EBX     ; virtual machine handle
ESI     ; points to a VCD_COM_Struc
EDX     ; port number
ECX     ; Byte_Input or Byte_Output value
AL      ; output data if ECX is Byte_Output
 
These procedures should return the AL register set to the input data if the
ECX register is equal to the Byte_Input value.
 
Uses
 
EAX, Flags
 
                                      ♦