Archived from groups: alt.comp.periphs.mainboard.asus (
More info?)
In article <clkipt$2fp1@imsp212.netvigator.com>, "Bronney Hui"
<bronney@netvigator.com> wrote:
> As subjected. As I noticed in Sissoft Sandra, only 1 root hub is marked
> 480Mbps. Aren't all 4 root hubs at USB 2.0?
>
> Thanks.
What you see is representative of how USB is wired up.
All ports on a Southbridge, share the same USB 2.0 logic block.
The logic block brings a max of 60MB/sec transfer rate, to
be shared over all the ports that are being run at USB 2.0.
If two disk drives are running USB Mass Storage protocol at
the same time (unlikely), then each will get 30MB/sec.
Since the PCI bus has a practical max of 100 to 110MB/sec,
you can see that the use of two USB 2.0 logic blocks, would
cause situations to arise where both logic blocks couldn't
run at full speed. AFAICT, that is the reason they don't do it.
Of course, there are some chips that do have interconnect
bandwidth to do more than PCI, but until very recently, no
company has invested design effort in doing higher speed
bridges in support of built-in peripherals. (Intel has
changed that, on the ICh5 and ICH6, but I don't know of any
other examples.)
USB 1.1 logic blocks are shared over two ports, so on an
eight port USB Southbridge, you will see four logic blocks
for them. When a port is "promoted" to USB 2.0, it is
connected to the USB 2.0 logic block, instead of its
original USB 1.1 block. Also, I don't think the ports
are "pure" in any sense - I think when a port starts
communicating with a USB peripheral, it may run in USB 1.1
mode for part of the initial setup, so I don't think it
is possible to have a chip that just does USB 2.0 protocol
only. (To research all of this, the specs are thick and
heavy!)
ICH5 (about 8MB and 671 pages - search for references to
266MB/sec):
http://developer.intel.com/design/chipsets/datashts/25251601.pdf
http://www.usb.org/developers/docs/usbspec.zip (USB 1)
http://www.usb.org/developers/docs/usb_20.zip (USB 2) 9MB!
Or something like that,
Paul
Facebook
Twitter
Instagram