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What Causes the Split Orphaned Packets that the Beagle USB 480 Protocol Analyzer Captures and Detects?

Question from the Customer:

I am using the Beagle USB 480 Protocol Analyzer, and have a question about the errors that the Data Center Software captures and reports. Following is a block diagram of my setup.

USB Test Setup with Beagle 480 USB Protocol Analyzer Figure 1: USB Test Setup

I see continuous split orphaned transactions on the Beagle analyzer when I plug a keyboard (or mouse) into the open port on the host controller. All of the split orphaned transactions are marked as errors by the Data Center Software. Can you help me understand what these transactions are?

Response from Technical Support:

Thanks for your question! When you connect the low-speed USB Keyboard to the hub, the host sends high speed split packets to the hub to provide control information about sending low packets to the keyboard. When the hub gets high speed packets from the host, the hub retransmits these high speed packets destined for itself to the high speed target device, that is connected to the Beagle analyzer through the high speed USB flash stick. Although the keyboard is not directly connected on the Beagle data path, the Beagle sees the split packets from the communication between the hub and the host.  This is completely normal behavior. If you would like to filter these transactions out, you can create an exception filter using the fields in the LiveFilter tab to easily remove them from your display. For more information about filtering, please refer to section 4.8 of the Data Center Software User Manual.

An example of this bus topology, which is similar to the setup that you are using, is shown in the figure below.

Example of USB Topology That Causes Orphaned Packets Figure 2: USB Topology That Causes Orphaned Packets

In summary:

  • SPLIT transfers are used by hosts to communicate with full-/low-speed devices through a high-speed hub. These transfers will have at least a Start SPLIT, and may include polling and handshaking as well.
  • Orphaned packets can occur when a device is connected through a path that does not pass through the Beagle analyzer.

For more information about USB transactions, please refer to section 6.6.3 of the Data Center Software User Manual and to the USB 2.0 specification.

Additional resources that you may find helpful include the following:

We hope this answers your question. If you have other questions about our protocol analyzers or other Total Phase products, feel free to email us at sales@totalphase.com, or if you already own one of our devices and have a technical question, please submit a request for technical support.