"VanguardLH" <VanguardLH@mail.invalid> wrote in message
news:Ob$f3XtSIHA.1184@TK2MSFTNGP04.phx.gbl...
> "Yousuf Khan" <bbbl67@yahoo.com> wrote in message
> news:ipSdnROWzJM6I-vaRVn_vwA@giganews.com...
>>I have two generic 4-port USB hubs that are supposed to be USB 2.0
>>compliant. The older one is fine, works as advertised. Meanwhile the newer
>>one sometimes shows up under the USB 2.0 root hub (i.e. "Standard Enhanced
>>PCI to USB Host Controller"), or usually it shows up under the slower
>>"Standard OpenHCD USB Host Controller" (USB 1.1).
>>
>> My motherboard (Asus M2NPV-VM) USB ports are all USB 2.0 compliant, and
>> they individually auto-detect whether they need to switch down to USB 1.1
>> speeds. I'm using a Microsoft tool called UVCView under Windows XP to
>> display the details of the USB devices, including the hubs and roothubs.
>>
>> According to UVCView, the older hub and newer hub seem to have the same
>> chipset vendor (idVendor = "Genesys Logic, Inc."), although externally
>> they look quite different and have different brand names. So I'm not sure
>> why one would be consistently USB 2.0 compliant, while the other one is
>> not.
>>
>> Now another interesting thing I noticed is that the inconsistent hub will
>> only show up as USB 2.0-compliant after I boot into Windows after having
>> previously rebooted from Ubuntu 7.10 Linux (dual-boot system). So maybe
>> Linux does something to the device that puts it right. But when I list
>> the devices while in Linux I see that it is listed under USB 1.1 just
>> like when in Windows. I have no idea why Linux leaves the hub fixed for
>> Windows, but doesn't fix it for itself?!
>>
>> Any idea what's going on with this hub?
>>
>> Yousuf Khan
>
>
> Are both of these a self-powered hub (i.e., they have a power adapter) or
> a low-power hub that relies on the current supplied from the USB
> controller at the motherboard? If they are bus-powered hubs, they CANNOT
> be on the same USB controller. Each controller provides 2 ports
> (channels) but these 2 ports still share the same controller and so both
> are limited by a total amperage that can be supplied by the same
> controller.

Sorry, but that isn't true. Bus powered hubs are deliberately limited to
100mA per port precisely so that they don't exceed the 500mA available from
the root hub port. You can connect 8 of them to the 8 ports of the USB2
enhanced root ports if you want to. The current available from any root
port is 500mA per port regardless of what is connected to the others. In
practice you can get a bit more than that before the over current protection
kicks in. Current not used on one port does not become available to the
others because the over current protection is implimented on a per port
basis.

Of course, what you can't do is to *cascade* bus powered hubs.