Virtual Com Port
A virtual port (VPort) is a data object that represents an internal port on the NIC switch of a network adapter that supports single root I/O virtualization (SR-IOV). Each NIC switch has the following ports for network connectivity:
One external physical port for connectivity to the external physical network.
One or more internal VPorts which are connected to the PCI Express (PCIe) Physical Function (PF) or Virtual Functions (VFs).
The PF is attached to the Hyper-V parent partition and is exposed as a virtual network adapter in the management operating system that runs in that partition.
A VF is attached to the Hyper-V child partition and is exposed as a virtual network adapter in the guest operating system that runs in that partition.
There are two types of VPorts:
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Default VPort
The default VPort provides network connectivity to the networking components that run in the management operating system. The default VPort has an identifier of NDIS_DEFAULT_VPORT_ID.
When the PF miniport driver creates and configures the default NIC switch, the driver implicitly creates the default VPort and attaches it to the PF. The default VPort cannot be attached to a VF.
The default VPort is always in an activated state and cannot be explicitly deleted. The PF miniport driver implicitly deletes the default VPort only when it deletes the default NIC switch.
For more information on how to create a NIC switch and the default VPort on the switch, see Creating a NIC Switch.
Nondefault VPort
Nondefault VPorts are not created implicitly when the NIC switch is created. An overlying driver, such as the virtualization stack, explicitly creates these ports by issuing OID method requests of OID_NIC_SWITCH_CREATE_VPORT. Nondefault VPorts may be attached to the PF or to a VF, and can only be created after the NIC switch has been created.
A nondefault VPort that is attached to a VF provides network connectivity to the networking components that run in the guest operating system. After it is created and attached to the VF, the nondefault VPort is in an activated state.
A nondefault VPort that is attached to the PF provides additional network offload capabilities to the networking components that run in the management operating system. For example, nondefault VPorts on the PF could be used to provide offload capabilities similar to the virtual machine queue (VMQ) interface.
Note Nondefault VPorts can only be created after the NIC switch has been created.
An overlying driver issues an object identifier (OID) method request of OID_NIC_SWITCH_CREATE_VPORT to create a nondefault VPort on a specified NIC switch. This OID request also attaches the created VPort to the network adapter's PF or a previously allocated VF.
The InformationBuffer member of the NDIS_OID_REQUEST structure contains a pointer to theNDIS_NIC_SWITCH_VPORT_PARAMETERS structure. After a successful return from the OID_NIC_SWITCH_CREATE_VPORT request, the VPortId member of the NDIS_NIC_SWITCH_VPORT_PARAMETERS structure has a VPort identifier that is unique across the VPorts on the NIC switch.
The overlying driver initializes the NDIS_NIC_SWITCH_VPORT_PARAMETERS structure with the configuration information about the nondefault VPort to be created. The configuration information includes the PCIe function to which the nondefault VPort is attached and the number of queue pairs for the nondefault VPort.
When it initializes the NDIS_NIC_SWITCH_VPORT_PARAMETERS structure, the overlying driver must do the following:
The SwitchId member must be set to the identifier of a NIC switch that was previously created on the network adapter through an OID method request of OID_NIC_SWITCH_CREATE_SWITCH.
Note Starting with Windows Server 2012, the SR-IOV interface supports only one NIC switch on the network adapter. This switch is known as the default NIC switch. When creating a nondefault VPort, the overlying driver must set the SwitchId member to the NDIS_DEFAULT_SWITCH_ID identifier.
The VPortId member must be set to NDIS_DEFAULT_VPORT_ID.
The AttachedFunctionId member must be set to the identifier of the VF or PF on which the nondefault VPort is to be attached.
A value of NDIS_PF_FUNCTION_ID specifies the PF. Otherwise, the value must be set to the identifier of a VF whose resources were previously allocated through an OID method request of OID_NIC_SWITCH_ALLOCATE_VF.
Note The attachment of a nondefault VPort to a VF or PF cannot be changed after the nondefault VPort has been created.
The overlying driver can also specify the number of queue pairs assigned to the VPort. A queue pair is a transmit and receive queue on the network adapter that is assigned to the VPort. If the network adapter supports asymmetric queue pairs for nondefault VPorts, the overlying driver may specify a different number of queue pairs for each VPort that the driver creates. For more information, see Symmetric and Asymmetric Assignment of Queue Pairs.
The overlying driver calls NdisOidRequest to issue the OID_NIC_SWITCH_CREATE_VPORT request to the underlying PF miniport driver. Before NDIS forwards the OID method request to the miniport driver, it does the following:
NDIS validates the parameters within the NDIS_NIC_SWITCH_VPORT_PARAMETERS structure. If the parameters are in error, NDIS fails the OID method request and does not pass the request to the PF miniport driver.
NDIS assigns an identifier for the nondefault VPort within the range from one to (NumVPorts– 1), where NumVPorts is the number of VPorts that the miniport driver has configured on the network adapter. The driver specifies this number in the NumVPorts member of the NDIS_NIC_SWITCH_INFO structure. The driver returns this structure through an OID query request of OID_NIC_SWITCH_ENUM_SWITCHES.
Note A VPort identifier of NDIS_DEFAULT_VPORT_ID is reserved for the default VPort that is attached to the PF on the default NIC switch.
The assigned VPort identifier uniquely identifies the nondefault VPort on the NIC switch of the network adapter.
- NDIS sets the VPortId member of the NDIS_NIC_SWITCH_VPORT_PARAMETERS structure with the assigned VPort identifier.
When the PF miniport driver is issued the OID request, the driver allocates the hardware and software resources associated with the specified nondefault VPort. After all of the resources are successfully allocated, the PF miniport driver completes the OID successfully by returning NDIS_STATUS_SUCCESS from MiniportOidRequest.
If the OID_NIC_SWITCH_CREATE_VPORT request is completed successfully, the PF miniport driver and the overlying driver must retain the VPortId value of the nondefault VPort for successive operations. The VPortId value is used during these operations:
NDIS and the overlying drivers use the VPortId value to identify the nondefault VPort in successive OID requests related to this VPort, such as OID_NIC_SWITCH_VPORT_PARAMETERS and OID_NIC_SWITCH_DELETE_VPORT.
During send operations, NDIS specifies the VPortId value to identify the VPort from which a packet was sent. This value is specified within the out-of-band (OOB) NDIS_NET_BUFFER_LIST_FILTERING_INFO data of the NET_BUFFER_LIST structure.
During receive operations, the PF miniport driver specifies the VPortId value to which a packet is to be forwarded. This value is also specified in the OOB NDIS_NET_BUFFER_LIST_FILTERING_INFO data of the NET_BUFFER_LIST structure.
The following points apply to the creation of nondefault VPorts:
Receive filters for media access control (MAC) and virtual LAN (VLAN) identifiers are configured on the VPort after it has been created. Overlying drivers dynamically set these receive filters by issuing OID method requests of OID_RECEIVE_FILTER_SET_FILTER. Receive filters can also be moved from one VPort to another through OID set requests of OID_RECEIVE_FILTER_MOVE_FILTER.
A nondefault VPort attached to the VF is in an activated state when it is created. The VPort cannot be deactivated if it is attached to the VF.
A nondefault VPort attached to the PF is in a deactivated state when it is created. An overlying driver, such as the Hyper-V extensible switch module, explicitly activates the nondefault VPort attached to the PF after the VPort has been created successfully. This is done by issuing an OID method request of OID_NIC_SWITCH_VPORT_PARAMETERS to the PF miniport driver.
When the overlying driver issues this OID request, it passes an NDIS_NIC_SWITCH_VPORT_PARAMETERS structure with the VPortState member set to NdisNicSwitchVPortStateActivated.
After a nondefault VPort is in an activated state, the PF miniport driver can allocate shared memory for the VPort by calling NdisAllocateSharedMemory. The driver must set the VPortId member in the NDIS_SHARED_MEMORY_PARAMETERS structure to the VPort's identifier value.
Note When a nondefault VPort is in an activated state, it is only set to a deactivated state when it is deleted through an OID set request of OID_NIC_SWITCH_DELETE_VPORT.
My question is similar to Setting up a virtual Com Port?, which has no answers.
I have software that can only print to a printer on COMx, a printer with a USB port, and a computer with a USB port but no serial ports, so the oft-suggested physical Serial-to-USB adapter isn't a solution. I'm looking for software that tricks Windows 7 into mapping a virtual COM port to a physical USB port. I'm certain that if the software I'm using sends its stream of bits to the USB port that the printer will work just fine. How do I trick the software into thinking it's printing to COMx when it's actually printing to USBx?
Internet searches only turn up drivers for some specific hardware Serial-to-USB adapter, but that's not what I'm looking for as I don't have that hardware. I found a Microsoft forum where they suggested changing the USB port's label in Device Manager, but we never found anything like what they described; perhaps that's possible with a different USB controller than we have.
4 Answers
There is a simple way to do it using standard Windows commands. Lee Harrison's link shows this command, but here's a short description. Start by making the printer shareable (from Printer Properties > Sharing tab).
Now, start a command prompt and type:
Here, pc_name is the name of the sharing PC, and printer_share_name is the share name you gave the printer when you set up the share.
From then on, anything you send to COM1 will be re-routed to the printer.
There is one proviso however - and it applies regardless of which method you use to get the data to the printer, hardware or software:
As your program only knows about COM1, I assume it will send plain text to the printer. Many USB-only printers do NOT understand plain text, and will just ignore it altogether. Printers that do this are called host-based printers, where the Windows graphics engine converts the page into dots on the paper, rather than letting the printer do the conversion. They are mostly the low cost printers, especially inkjets but also some lasers. Printers that do understand text need to support a language called PCL5. PCL6 printers usually also support PCL5, but PCL3 printers do not.
If you tell me your printer model I can check what language it supports.
We use this solution in the company.
Virtual COM port (VCP) drivers cause the USB device to appear as an additional COM port available to the PC. Application software can access the USB device in the same way as it would access a standard COM port.
Here is the Instalation Guide.
This is a very specific scenario, but the following directions may work for you:http://www.decompile.com/dataflex/tips/usb_printer.htm
Directly from that link:
However, I don't know if COM connections will even be selectable in your case since your PC doesn't have any to begin with. You may be able to purchase a USB/COM adapter just to gain access to these values, then use the above directions to forward to your USB printer.
Sounds kinda hack-ish but when you're running old software sometimes this is what it comes down. Whatever the solution, I don't know that it will appear to be elegant!
The final thing would be to just purchase a USB to serial/parallel adapter and a cheap printer that fits the specs. If you use this software in business, I think that's an easily justifiable expense.
If you need to emulate the serial port, this software make that kind of work https://www.eltima.com/products/vspdxp/ But I have no idea, whether you can talk to your USB with the emulated COM..
protected by Community♦May 15 at 12:47
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