MUTT devices

MUTT is the acronym for Microsoft USB Test Tool (MUTT). The MUTT software package contains several test tools and drivers that let hardware test engineers test interoperability of their USB controller or hub with the Microsoft USB driver stack. The test tools validate USB host controller software, hardware (including firmware) and any USB hub that is installed between the host controller and the device.

The MUTT software package works with a test device that is called the MUTT device. MUTT is the first USB test device that was designed by Microsoft.

There are four different types of MUTT devices in production. Of those devices, two types are designed to test USB devices and the other two types are focused on USB hubs.


  • Based on the design of the CY3681 EZ-USB FX2 Development Kit (Cypress FX2).
  • Compatible with FX2 capabilities, such as high speed and full speed transfers to bulk, isochronous, control, interrupt endpoints.
  • Simulates traffic from USB 2.0 devices.

    MUTT Device


The MUTT Pack is a combination of a USB 2.0 hub and an FX2 device that controls the hub and acts as a downstream device.

  • Based on the design on the Cypress Hub and Cypress FX2.
  • Hub capabilities. This can operate as a multi-TT or single-TT high speed hub; simulates overcurrent.
  • Exposes a downstream port that can be turned on or off.
  • Simulates USB 2.0 hub behavior.
  • Can operate in self-powered or bus-powered modes.

    MUTT Pack Device

The MUTT Pack has two USB connectors. The standard B connector is used to plug the MUTT Pack in to the host system. The standard A connector is downstream of the embedded hub on the MUTT Pack, and can be used for additional device testing (discussed later in this document).

MUTT Pack Connectors

How to power the MUTT Pack

The MUTT Pack uses a small jumper (see Figure 3) to switch between self-powered and bus-powered modes. In bus-powered mode, the USB bus of the host system powers the MUTT Pack. In self-powered mode, the MUTT Pack is powered with an external power adapter, such as the one listed on this Website.

MUTT Pack Powering Flowchart

Use the following flow chart to determine how to power the MUTT Pack:

Note  Do not use the MUTT Pack without the power jumper.

Incorrect Usage

This image shows how to use the jumper for powering the MUTT Pack by the USB bus of the host system:

MUTT Pack Bus Powered

This image shows how to use the jumper for powering the MUTT pack with an external power adapter:

MUTT Pack Self Powered

Note  Disconnect any existing power adapters and the cable to the host system when you are changing the jumper on the MUTT Pack.


  • Based on the design of FX3 EZ-USB FX3.
  • Implements SuperSpeed features such as the bulk streams feature.
  • Simulates USB 3.0 device traffic.
  • Note: this device does not support operation at Full Speed at this time.


SuperMUTT Pack

The SuperMUTT Pack is two devices in one. It is a USB 3.0 hub with a Cypress FX2 device downstream. The device controls the hub and also acts as a downstream device. The SuperMUTT Pack simulates USB 3.0 hub behaviors.

Note  The downstream device is a 2.0 device, not a USB 3.0 device.

SuperMUTT Pack

How to get MUTT devices

Order MUTT devices from here:

MUTT deviceManufacturer
MUTT JJG Technologies
MUTT Pack JJG Technologies

JJG Technologies


SuperMUTT Pack

VIA Labs


Related topics

Test with Microsoft USB Test Tool (MUTT)



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