What's the normal behavior of connecting USB2 devices to a USB3 hub?

Discussion in 'Mac Accessories' started by Makosuke, Feb 21, 2015.

  1. Makosuke macrumors 603

    Joined:
    Aug 15, 2001
    Location:
    The Cool Part of CA, USA
    #1
    I was just diagnosing a sleep problem that turned out to be caused by a malfunctioning iDsonix USB3 hub, but in the process I noticed an unrelated weird behavior, and I'm wondering if it's the hub, if there's actually something wrong with my computer (5K iMac), or if this is expected OS X behavior. If you've got a USB3 hub and at least one USB2 and USB3 device handy, it'd be easy to test.

    The behavior I'm seeing: If I plug the USB3 hub into a port on the computer, then immediately connect a USB2 device to the hub, it works fine (at USB2 speeds, of course). However, subsequently, no USB3 devices, at all, will work on that port until it's been disconnected. Not just the hub, but the port on the back of the computer itself--if you plug a USB3 device into the hub, or swap the cable from the hub to another USB3 device, the computer completely ignores it.

    Unplugging the USB plug from the back of the computer, however, and re-connecting it to the same port, appears to reset that port and cause it to again function normally.

    If, however, I first plug a USB3 device into the USB3 hub, it shows up as a USB3 hub and behaves normally. If I subsequently add USB2 devices, they appear in the device tree as a being connected to a separate USB2 hub, but the USB3 hub doesn't disappear, even if there are no USB3 devices connected, so the hub acts normally.

    Basically, this hub is acting like its USB controller is "asleep" and doesn't show up to the computer at all until at least one device is connected. When a device is connected, it will register USB2 or USB3 hubs as necessary to support the device(s) connected to it. But if that first device is a USB2 device, the only hub the computer will see is a USB2 hub, and the computer will subsequently disable the USB3 pins on that port, although the connected device thinks it's a USB3 port. Disconnecting the cable from the back of the computer appears to reset the port, but disconnecting the B end from the device does not.

    I could imagine this being an OS/firmware issue. I could also imagine this being a weird glitch that results from an OS/firmware peculiarity that's the result of this particular hub's chipset doing unusual things in order to save power or something.

    What's the behavior you're seeing? This, or does it behave like you'd expect? Note, again, that once the port has had a USB3 device connected to it once, it will behave normally until you physically disconnect the USB cable from the back of the computer--even connecting the device at the other end to swap to another device won't do it. So it'd be easy to test a USB3 device once, leave it plugged in, and never notice subsequently.
     
  2. blueroom macrumors 603

    blueroom

    Joined:
    Feb 15, 2009
    Location:
    Toronto, Canada
    #2
    I have an Anker USB 3.0 three port hub + GigE. It works fine with USB 2 or 3 devices plugged in as you described on my rMBP 2013.

    Which iDsonix USB 3 hub do you have?
     
  3. Makosuke thread starter macrumors 603

    Joined:
    Aug 15, 2001
    Location:
    The Cool Part of CA, USA
    #3
    The 10-port black one they currently sell (it has three banks you can turn off with manual switches). It uses the VIA VL812 chipset.

    The hub recently started malfunctioning, so it's possible that it's just flat-out broken, or it could be specific to the chipset itself. I won't really be able to test until I get a replacement.
     
  4. ColdCase macrumors 68030

    Joined:
    Feb 10, 2008
    Location:
    NH
    #4
    Normal behavior for USB3 is quirky... so yes what you observe is normal :) My 7 port pluggable USB3 hub seems to work fine as long as I limit the number of attached drives to two, sometimes three. Any more than that issues seem to pop up. Works just fine with 7 printers, CD drives, Mice, keyboard, iDevices... only when drives are connected do thinks go south. My 4 port Belkin USB3 hub does the same thing. My older USB2 hubs are more solid (USB2 being so much more simple).

    No issues with the five USB ports on my TB dock, but thats different.
     
  5. Makosuke thread starter macrumors 603

    Joined:
    Aug 15, 2001
    Location:
    The Cool Part of CA, USA
    #5
    Thanks for the feedback, ColdCase. I'm interested in comparing the chipset used, since it sounds like blueroom isn't seeing this particular weird behavior, so just to be clear, are both of your hubs doing this exact same thing, or is it just the Belkin doing this, while the 7-port one is acting up in other ways?

    Also, any idea what chipset either of your hubs uses? (Belkin doesn't tell you, but you can usually check in System Profiler, if you don't mind taking the time to do that.)

    It occurs to me that the reason the aforementioned USB+eithernet hub might not display the problem, if it's indeed more common, is that the ethernet port is just another USB3 device on the bus, so when the hub is connected the computer immediately recognizes the connected device as being USB3, which would eliminate the issue.
     

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