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Should the USB device to go into suspend when the USB host is suspended?

Discussion in 'Embedded' started by Sivaraj, Nov 30, 2006.

  1. Sivaraj

    Sivaraj Guest


    Is it necessary/MUST for the USB device to go into suspend when the USB
    host is suspended, provided that the device is Remote-Wakeup Enabled?
    What the spec says?
    Sivaraj, Nov 30, 2006
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  2. Sivaraj

    Sivaraj Guest

    Can anybody please share your views on this?
    Sivaraj, Nov 30, 2006
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  3. Sivaraj

    Arlet Guest

    Don't top-post. Have some patience (24 hours is a good time to wait).
    Make sure you provide necessary details for the answer. For example,
    what "host" and what "spec" are you talking about ?
    Arlet, Nov 30, 2006
  4. Sivaraj

    Jeff Kellam Guest

    You can get a copy of the spec from
    http://www.usb.org/developers/docs/ which should answer your questions
    Jeff Kellam, Nov 30, 2006
  5. Sivaraj

    Elan Magavi Guest

    Top posting is ok with me..

    I suspect he posted here because he was in a situation where he needed the
    answer quickly. Been there.

    I believe the answer to his question , though.. is a simple . 'no'
    Elan Magavi, Nov 30, 2006
  6. Sivaraj

    Sivaraj Guest

    Host -> PC
    Spec -> USB spec

    I am sorry for the top-post, i am new to this. Also i needed the answer
    in quick time, i will correct myself when i post in future.. Thanks for
    all your responses. Then the spec doesn't hav the info i am looking.
    Actually I am testing a scenario where I am suspending the host PC and
    observing the behavior of the attached USB device. I want to know this:

    When I suspend the host the USB bus will be suspeneded, So if any
    connected USB device will not get the bus power during this period, in
    this case, what should be state of the device, should the state be
    suspended or normal?
    Sivaraj, Dec 2, 2006
  7. Sivaraj

    CBFalconer Guest

    "what host" includes at least the OS in use. For example, Linux
    (and which one), FreeBSD, OS2, Winslush, etc. After that what
    hardware, i.e. CPU, chipset, manufacturer (i.e. what bios), etc.

    For USB specifications I suggest google. The specification is
    public, but I can't give you a URL. Most systems can (not
    necessarily do) supply USB power from the auxiliary supply, even
    when turned off. This is often configurable.
    CBFalconer, Dec 2, 2006
  8. Sivaraj

    Arlet Guest

    As far as a USB device is concerned, it must go into suspend mode when
    it detects "suspend signalling" on the bus, and stay active at any
    other time.

    When a host goes into suspend mode, this is a completely unrelated
    event, which just happens to use the same word. A host in suspend (or
    any other power save state), has 3 options as far as the USB bus is

    1) let it stay awake
    2) let it go to USB suspend
    3) remove power

    In the second case, the devices will still be able to receive power
    from the USB bus, but at a much reduced current (2.5mA max for devices
    supporting remote wakeup).

    In the third case, the device will be reset and reconfigured when power
    is restored, even when it is self-powered.

    What the host does with the USB bus depends on the OS, hardware, and/or
    user settings. If you're using Windows, you can probably find
    information regarding power management on the microsoft.com site.
    Arlet, Dec 2, 2006
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