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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.
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 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. For more information about the callback procedure, see the following “Comments” section.
If the carry flag 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. |
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.
EAX ; IRQ handle
EBX ; virtual machine handle
ESI ; points to a VCD_COM_Struc
For more information about the actual entry parameters and return values, see Chapter 18, “Programmable Interrupt Controller.”
The following callbacks have default actions, if the callback offset is set to 0:
| Callback | Default action |
| VPS_EOI_Proc | Executes a physical EOI and clears the interrupt request. |
| VPS_Hw_Int_Proc | Assigns an owner to the current virtual machine if not owned, and requests an interrupt in the owner's virtual machine. |
| VPS_IRET_Proc | Is not virtualized. |
| VPS_Mask_Change_Proc | Assigns the owner to the current virtual machine if not owned. |
| VPS_Virt_Int_Proc | Is 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_IER
VPS_In_IIR
VPS_In_LCR
VPS_In_LSR
VPS_In_MCR
VPS_In_MSR
VPS_In_RxTxB
VPS_Out_IER
VPS_Out_IIR
VPS_Out_LCR
VPS_Out_LSR
VPS_Out_MCR
VPS_Out_MSR
VPS_Out_RxTxB
These callbacks have the following parameters:
EBX ; virtual machine handle
ESI ; points to 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.
EAX, Flags