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  1. #1
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    USB Bandwidth (2.0)

    Is there any way to alter the system bandwidth allocation for USB ports?

    The built-in ports on my machine are USB 1.1. So I have acquired a USB 2.0 cardbus adapter - with a two-port dongle. If, however, both ports on the card are used, performance degrades. The bandwidth allocation for the controller with one device attached is 10%; with two devices it goes up to 12%. OTOH, the USB 1.1 port gets 20% for an Optical Mouse - resulting in the well-known periodic "jackrabbit on steroids" performance.

    I have tried disabling unused USB Host Controllers, but that does not seem to impact the situation at all. Google seems to yield nothing specific on this issue. Any ideas - short of buying another adapter?
    Gre

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    Re: USB Bandwidth (2.0)

    Well you should be able to use several USB devices with no problem. I thought that was the whole Idea of USB. I use nothing but USB and have had no such problems. May be time for another adapter or maybe it's a driver problem.

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    Re: USB Bandwidth (2.0)

    Have you checked the current draw for your USB devices? Perhaps one of them is sucking too much power through the line, causing your degradation.
    -Mark

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    Re: USB Bandwidth (2.0)

    unk~,

    You aren't trying to use USB 1.1 devices on a 2.0 port and expecting to get any better performance there, are you?

    Bob
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    Long ago, there was a time when men cursed and beat on the ground with sticks. It was called witchcraft.
    Today it is called golf!

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    Re: USB Bandwidth (2.0)

    I just read this at Windows Update # 822603 Anyway that update has to do with USB 2.0 problems. Here some of it below.
    Attached Images Attached Images

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    Re: USB Bandwidth (2.0)

    As we know,WinXP kvetches when a USB 2.0 device is attached to a USB 1x connection. This hasn't happened.

    The USB 2.0 HotFix 822603 - spotted by <!profile=cowboydawg>cowboydawg<!/profile>'s eagle eye - was installed several weeks ago.

    I'm not quite clear what is meant by "current draw" for USB devices? How do I find the measurement of this?

    The only statistics I could locate were on the Advanced tab of the USB Controller Properties in Device Manager. It appears that - somewhere in the plumbing - a built-in USB port can get 20% bandwidth (far to much for an optical mouse <img src=/S/grin.gif border=0 alt=grin width=15 height=15>). OTOH something connecting through a PCMCIA port - using a (new) USB 2.0 adapter gets a default of 10%, which grudgingly climbs up to 12%; degrading performance. Is there anywhere the controls for this "plumbing" can be accessed?
    Gre

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    Re: USB Bandwidth (2.0)

    I'll try to hunt up some sources--it'll be a hunt more than a good feel from practical experience other than using USB devices. This is probably a very simple explanation considering the places where you're looking but I did spot this on a Tech TV writeup:

    George in Braintree, Massachusetts, wants to know the limits of USB.


    According to the specification, USB can handle up to 127 peripherals. In the real world, the limit needs to be considered with the bandwidth of USB.


    USB has a bandwidth limit of 12 megabits per second. This bandwidth is shared bandwidth, meaning that every device on the chain uses the same bandwidth pipe. The more devices you use at the same time, the slower your connection. Also, consider that some devices use more of the bandwidth than others.


    Some computers with USB share a single USB channel, while other computers have a separate channel for each USB port.


    SMBP

  8. #8
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    Re: USB Bandwidth (2.0)

    As wild a stab as this is, if you look at some of the data from Aida 32 can it indicate or reflect your draw? I don't know where this info would be accessed or more importantly what you want to do is adjust it.

    Invisible Dream

    How Far Can You Go With USB

    USB: A Low Cost Connection for Low bandwidth devices

    SMBP

  9. #9
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    Re: USB Bandwidth (2.0)

    The current required for a USB device can be found in Device Manager > USB Root Hub > Properties > Power

    StuartR

  10. #10
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    Re: USB Bandwidth (2.0)

    Thanks for the further feedback.

    The available Power is 500 mA per Hub. On the USB 2.0 adapter/PCMCIA, the webcam takes 400 mA and the scanner takes 10 mA (when idle).

    I don't know whether the attached graphic will help:<UL><LI>There are 4 USB ports: <UL><LI>2 x 1.1 - marked in black <LI>2 x 2.0 - marked in red[/list]<LI>The Device Manager shows 3 Controllers and Hubs for each pair of ports.<LI>All Hubs show 500 mA available Power. <LI>Only the 2nd and the 6th Hub show as having anything attached - although all 4 available slots are being used. <LI>The 2nd Hub shows 100 mA for each of an Optical Mouse and the Composite Device (a PS2 to USB connector). <LI>The 6th Hub shows the webcam and scanner - as above.<LI>When the scanner is connected, the webcam preview in Windows Explorer changes from full motion preview to a whited out screen.<LI>The Controllers marked in pink register as 10% bandwidth - which appears to be the default.<LI>The 1st Controller (B1) goes up to 11% with the webcam attached and to 12% when the scanner is also connected.<LI>The 5th Controller bandwidth goes up to 20% for the Optical Mouse and goes to 23% when the Composite Device (leading to a Natural Keyboard and an old PS2 Mouse) is attached.[/list]The impact of the idle scanner seems disproportionate.

    The bandwidth allocated to the Optical Mouse seems disproportionate.

    Disabling the "unused" Hubs and Controllers seems to have no impact.

    Any ideas?
    Attached Images Attached Images
    Gre

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