Using ACPI to Configure USB Ports on a Computer

If the system requires ACPI BIOS changes to accurately reflect the USB port configuration, you should consider the user's ability to connect a device to the port when you configure the port.

If you use ACPI to specify the configuration of a USB port, you must define the USB port capabilities (_UPC) and physical location description (_PLD) objects. Although the ACPI 3.0 specification does not specifically prohibit the use of only the _UPC object, the use of both objects more precisely indicates the user's ability to connect devices to the port. Using only the _UPC object might not set the device container grouping correctly or as expected.

Devices that are attached to the port are removable from the hub if the DeviceRemovable bit is set. The following table shows how the values of the ACPI objects for a given port affect the value of the USB hub descriptor DeviceRemovable bit that Windows reports for the device.

USB Port StatusExample_UPC.PortIsConnectable byte_PLD.UserVisible bit (bit 64)Resulting DeviceRemovable Bit Value

Port is visible and the user can freely connect and disconnect devices.

Port is exposed on the face of a panel on the computer that is visible to the user.

Set (OxFF)

Set (1)

Set

Port is hidden or internal and user cannot freely connect and disconnect devices.

Port is directly hard-wired to an integrated device, such as a laptop webcam or an internal USB hub.

Set (OxFF)

Cleared

Cleared

Port is physically implemented by the USB host controller, but is not used.

Port is an excess port that is not connected to a port plug terminal or an integrated device.

Cleared (0x00)

Clear

Cleared

 

Note   It is an invalid configuration to define a port as not connectable but visible to the user.

The following examples show correctly formed ACPI Source Language (ASL) that demonstrates the use of the _UPC and _PLD objects to describe a USB port:

  • To specify a port that is internal (not user visible) and can be connected to an integrated device, the _UPC.PortIsConnectable byte must be set to 0xFF and the _PLD.UserVisible bit must be set to 0.

    In the following example the device is grouped with the computer's device container.

    
    Name(_UPC, Package(){
        0xFF,         // Port is connectable
        0xFF,         // Connector type (N/A for non-visible ports)
        0x00000000,   // Reserved 0, must be zero
        0x00000000})  // Reserved 1, must be zero
    
    Name(_PLD, Buffer(0x10){
        0x81, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x30, 0x1C, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00})
    
    
  • To specify a port that is external (user visible) and can be connected to an external device, the _UPC.PortIsConnectable byte must be set to 0xFF and the _PLD.UserVisible bit must be set to 1. The _UPC.PortConnectorType byte must be set to the appropriate USB connector type as specified in Section 9.14 of the ACPI 3.0 specification.

    In the following example the device is assigned a new device container and is displayed as a separate physical device.

    
    Name(_UPC, Package(){
        0xFF,         // Port is connectable
        0x00,         // Connector type, Type 'A' in this case
        0x00000000,   // Reserved 0, must be zero
        0x00000000})  // Reserved 1, must be zero
    
    Name(_PLD, Buffer(0x10){
        0x81, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x31, 0x1C, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00})
    
    

For more information about the ACPI 3.0 interface, see Advanced Configuration and Power Interface Specification Revision 3.0b.

 

 

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