USB 3.0 debugger through a USB 2.0 port is not supported on Intel System-on-Chip (SoC) devices in Windows 8.1

Applies to: Windows 8.1 EnterpriseWindows 8.1 ProWindows 8.1

This article describes an issue that occurs when you try to use the USB 3.0 debugger. We have released an update to resolve this issue. Before you apply the update, check out the Prerequisites for hardware settings in this article.


Consider the following scenario:
  • You have an Intel® Atom™ Processor Z373x series based or Intel Cherry Trail Cost Reduction (CHT-CR)-based computer that is running Windows 8.1.
  • The computer has an external USB 2.0 port.
  • You try to perform kernel debugging on the device by plugging a USB 3.0 cable into the USB 2.0 port.
In this scenario, the debug fails.


This issue occurs because Intel® Atom™ Processor Z373x and CHT-CR platforms do not provide xHCI debugging support because of pin reduction.


To resolve this issue, you can use one of the following methods.

Note After you apply this update, you can perform kernel debugging on Intel® Atom™ Processor Z373x and CHT-CR devices by plugging a USB 3.0 cable into the external USB 2.0 port. This feature is also supported on full Intel® Atom™ Processor Z374x, Z377x, Z378x, Z379x or N28xx/N29xx and CHT devices when plugging a USB 2.0 cable into the external USB 3.0 port, because the external USB 3.0 port is backward-compatible with USB 2.0.

Method 1: Windows Update

This update is available from Windows Update.

Method 2: Update Rollup

To resolve this issue, install the November 2014 update rollup for Windows RT 8.1, Windows 8.1, or Windows Server 2012 R2.

Prerequisites for hardware settings

To apply this update, you have to meet the following conditions:
  • The firmware should have the Extensible Device Controller Interface (xDCI) Debug Port Table 2 (DBG2) entry.
  • The xDCI controller is exposed correctly to the desired USB debug port.
  • The OEM firmware has to hide the xDCI controller in PCI, or expose it as an ACPI device instead of as a PCI device.

    Note The base address for xDCI will be pointed to by the DBG2 table entry.
  • The USB cable should be plugged in before the platform starts.


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

See DBG2 spec to check for more information.

The following table contains the important fields for the xDCI DBG2 table entry:
Important FieldValue
AddressSpaceIDSystemMemory (0)
Register_Bit_Width32 bits (0x20)
BaseAddressRegister<Dynamically Assign based on xDCI PCI BAR0>
Port TypeUSB (0x8002)
Port SubtypeSynopsys xDCI (0x0007)
This update also contains two other important fixes that target the Intel SoC devices:
3002859 Miracast display resolution changes after you shut down and then start a Windows 8.1-based computer
3008242 The system does not enter Connected Standby after you install update 2996799 in Windows 8.1


See the terminology that Microsoft uses to describe software updates.