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TUSB8020B: FW behavior when host cannot resolve USB2.0 connection with peripheral

Jay Jang
Intellectual 915 points
Part Number: TUSB8020B

How does this part communicate with the host when the peripheral connection is always expected to be USB3.0 superspeed?

In the event of failure to establish USB3.0 super speed connection the host will revert to USB2 but the customer would like the hub to toggle the GPIO and reset the connection instead reverting to USB2

Can you provide information on how this USB hub behaves in this scenario?

  • 0
    TI__Guru* 76130 points
    Hello,
    Any USB3.0 peripheral will try to connect at USB3.0 at power-on, after the timer expires the peripheral will drop to USB2.0, this is required and specified by the USB3.0 Specifcation.
    The TUSB8020B will not reset the link if the device drops to USB2.0.
    You can set some software to be polling the xHCI controller registers to know when a device drops to USB2.0
    Regards
  • 0 in reply to Elias Villegas M.
    TI__Intellectual 915 points
    Sorry, I mixed up the requirement... in the case that it is the opposite- the device IC has only USB 3.0, and connects to the host over a regular USB 3.0 cable.

    If the host drops the 3.0 connection or the cable has intermittent connection, can the hub chip assert a signal to indicate this status?
  • 0 in reply to Jay Jang
    TI__Guru* 76130 points
    Hello,
    The only status options on the hub are terminals: SS_DN1, SS_DN2, SS_UP and HS_UP.
    If the hub has a USB3.0 upstream connection and then that connection drops to high-speed then the SS_UP and HS_UP pins will toggle.
    Regards
  • 0 in reply to Elias Villegas M.
    TI__Intellectual 915 points
    The datasheet reads : "When the upstream port is connected to an
    electrical environment that only supports high-speed
    or full-speed/low-speed connections, SuperSpeed
    USB connectivity is disabled on the downstream
    ports"

    Is there a way to change configure this to disable HS when only a SS connection is supported upstream?

    I couldn't find anything thing in the configuration tables showing this option for the control registers.
    Would we be able to implement this through an OTP or would it require a HW change?
  • 0 in reply to Jay Jang
    TI__Guru* 76130 points
    Hello,
    No, there is no option to disable HS as that would violate the USB3.0 spec.
    If you don't need HS you can route only the superspeed lines.
    Regards
  • 0 in reply to Elias Villegas M.
    TI__Intellectual 915 points
    Not routing the HS lines would also violate the spec, correct?
    If you can confirm this i will let the customer that our part will not work.
  • 0 in reply to Jay Jang
    TI__Guru* 76130 points
    Is the USB certification required?
    The hub does not support disable the HS interface because that won't meet the USB spec, but if USB logo is not required then they can disconnect the HS lines and the system will work at SS only.
    Of course there are interoperability concerns because any USB3.0 device will expect to connect at HS if SS is not available or timed-out.
    I want to be clear that this is not a limitation of our device but a non-compliant application.

    Regards