Re: [gentoo-user] Re: Which USB device on which controller?

[Grant <emailgrant@gmail.com>]

>>>>>> Sounds like it's a 1.1 device to me.
>>>>>
>>>>> Yep, that's what it sounds like to me too.
>>>>>
>>>>> Dale
>>>>
>>>> But that's OK isn't it?  I don't need 2.0 speeds between each webcam
>>>> and the controller, I just need the increased overall bandwidth of a
>>>> 2.0 controller so one of the 1.1 webcams doesn't use all of it.
>>>
>>> The 2.0 controller doesn't _have_ increased bandwith if it's
>>> talking to 1.1 devices.  In that case, the 2.0 controller is
>>> transferring data at the same speed as a 1.1 controller.
>>
>> I thought the total bandwidth available for a controller was different
>> than the bandwidth at which it communicates with one device.  You're
>> saying any 1.1 device that uses 12 mbit/s will 100% monopolize a 2.0
>> controller so no other devices can function?
>>
>
> Yes. USB is not like 1394/Firewire. Firewire will increase and
> decrease bandwidth as different devices take control of the bus. There
> is negotiation between devices and the device that owns the bus
> controls how the bus is used.
>
> With USB a 1.1 device on the bus causes the 2.0 controller to operate
> at 1.1 speed so there is only 12Mb/S on that bus once you plug the 1.1
> web cam in.
>
>> Taking a different approach, since I have 2 USB controllers (EHCIx1,
>> OHCIx1) why can't I operate one webcam on one controller and one
>> webcam on the other controller so they can both function?
>>
>
> If the hardware is working correctly, if the drivers are independent,
> and IF IF IF the two physical ports you chose are actually going to
> completely different controllers then you can. I do this. This sort of
> thing becomes an issue with USB when you make a mistake an plug an old
> USB mouse or keyboard into the wrong physical port and bring your 2.0
> bus speed down to 1.1 bandwidth.

That's a lot of IFs.  This USB PCI card looks good because it claims:

"Five ports in three independent host controller design, two OHCI and one EHCI"
http://www.newegg.com/Product/Product.aspx?Item=N82E16815104202

Are you saying I can't count on this card behaving as 3 separate USB
controllers?

- Grant


> Over and out,
> Mark
>
>> - Grant
>>
>>>> I get the feeling I have a misconception somewhere along the
>>>> line here. Could someone straighten me out?
>>>
>>> A Corvette going 3MPH will get to the finish line at exactly
>>> the same time as a 4-year-old kid on a tricycle going 3MPH.  It
>>> doesn't matter what the controller is capable of -- it matters
>>> what speed it's actually talking.
>>>
>>> --
>>> Grant