Dear sir,
We recently discovered a strange issue with the TUSB8041 USB 3.0 hub controller. We have designed a USB 3.0 hub PCB based on TUSB8041 controller. There are 2 USB 3.0 cameras connected to this USB hub PCB. The up stream port is connected to the PC. In normal mode of operation the data from the 2 USB camera's are streamed to the PC (we use USB 3.0 port on PC). In the normal model of operation everything works as expected.
Recently we however discovered that connectivity with the USB camera's is lost under the following conditions:
- Both camera's stream the image data to the PC through the USB hub. The hub is connected to a USB 3.0 port of the PC.
- Unplug USB cable while both camera's stream data to the USB. In device manager you will see that USB hub and camera's disappear.
- Restore USB cable connection. The USB hub drivers pop up in device manager, however this time the drivers of both camera's are not loaded. Or if it is loaded then windows report unknown device.
- If you unplug all down stream USB devices (i.e. both camera's) and restore connection again, windows 10 keep reporting that devices are unknown or that there is a problem with device.
- If you then connect another USB 3.0 device, we notice the same problem. We have attached a USB 3.0 harddisk.
- Note that if you connect a USB 2.0 device, then it operates OK. So it looks like that the USB 3.0 port on the TUSB8041 is disrupted and that all USB 2.0 downstream ports work fine.
- Unplugging all USB cables (up stream and down stream) and reconnecting will not solve the issue. We have also rebooted PC but this also doesn't help. Only way to recover is power cycle the USB hub.
We have repeated above experiments by connecting the USB hub to an upstream USB 2.0 port on the PC. Then we noticed that the above-mentioned problem does not occur.
Lastly I can provide following details:
- USB hub is self powered.
- The upstream VBUS line is connected to VBUS pin of TUSB8041 by a resistor divider (design is identical as reference design of TI).
- The downstream ports are powered from the local 5V board power supply. This power supply is independent of VBUS. So if upstream VBUS disappear (by disconnecting USB cable) then downstream ports VBUS are still powered with 5V.
- From the USB 3.2 protocol standard I understand that if VBUS is low then all state machines of down stream and upstream ports should reset to a default state. This apparently does not happen.
I have following questions:
- Can you explain why the TUSB8041 controller behaves as described above?
- Is this a silicon bug? Are there errata of the TUSB8041?
- Is there a work around for this problem?
Best regards,
Guo