USB source auto-selection bug

I’ve reported a USB hub auto-selection bug to the Support team, but wanted to mention it here in case anyone else has similar issues.

Problem Setup

I have the following devices connected to the Spectrum:

  1. MacBook Pro, using a single 40Gbps USB-C cable for video, USB data and power delivery. Spectrum is in refresh rate priority mode.
  2. Windows laptop with eGPU. DisplayPort cable is connected to the GPU in the eGPU case. USB-B cable is connected to the laptop.

Both the video source and USB hub source settings are set to automatic selection.

What Actually Happens

Automatic hub source selection is inconsistent.

Scenario 1:

  • MacBook is connected, powered on.
  • Windows laptop is turned off and disconnected from both eGPU and USB-B.
  • eGPU is still connected via the DP cable, but is not powered on.

The Spectrum correctly uses the USB-C connection for both video and USB hub source.

Scenario 2:

  • MacBook had been running but is sent to sleep. It remains connected to the USB-C cable.
  • Windows laptop is connected to eGPU and USB-B and is turned on.
  • eGPU case is connected via the DP cable and powers on with the laptop.

The Spectrum correctly uses the DP connection for video, but continues to use USB-C for the hub source. If the OSD is used to reselect automatic selection, it appears to restart the selection process and the USB-B connection is used.

Scenario 3:

  • MacBook is disconnected, but the USB-C cable remains plugged in.
  • Windows laptop is connected to eGPU and USB-B and is turned on.
  • eGPU case is connected via the DP cable and powers on with the laptop.

The Spectrum correctly uses the DP connection for video. It refuses to automatically change to USB-B as the hub source, even when using the OSD to reselect automatic selection. Hub source has to be manually changed to USB-B.

Note: I don’t think that the eGPU case has any specific impact on the problem. It will likely still occur when using a standard PC that gets turned on/off but remains connected.

What’s Expected To Happen

The USB hub changes automatically depending on the video input.

  • When the USB-C connection is selected for video, it should also be used for the USB hub source.
  • When the DisplayPort connection is selected for video, the USB-B port should be used as the USB hub source.
  • Automatic hub selection should work regardless of whether the video source is selected manually or automatically.

Alternatively, it should be possible to set a USB hub source for each video input. When the video input changes (either automatically or manually), the associated hub source is used.

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