USB Bandwidth with 56 devices

[onsetcomp]

Our engineering dept is using 56 USB devices on one XP Pro SP2 PC and need some help. The specs state that 126 USB can be connected at once. This is a test system for products we manufacture.

If we look at the Advanced tab of the USB Universal Host Adapter it shows Bandwidth Used for the System in a percent. On one system it shows well over 100% and on others its like 10%, 20% and that changes by 10% by plugging in a USB mouse. Why would this data be different when swapping out the PC and having the same number of USB devices connected?

Does anyone have detailed info on USB and what this bandwidth info is?

 

[rislejay]

Check out this website,

http://www.usb.org/about/faq/

 

[bcastner]

• Bandwidth Usage• The Device Manager property page for USB host controllers contains an Advanced tab, which displays the bus bandwidth that is consumed by USB devices. The USB bandwidth usage that is displayed for a USB 2.0 Enhanced Host Controller is not correct. A future version of the Windows operating system will correctly calculate bandwidth usage for high-speed USB devices.
• Bandwidth calculations for single/multi-TT hubs will be addressed in a future release of the Windows operating system....

• The bandwidth reporting user interface is not supported on high-speed host controllers. The bandwidth user interface (in the host controller’s Advanced tab in Device Manager) may show incorrect bandwidth usage on Windows XP. Microsoft may add smarter algorithms for calculating bandwidth usage downstream of an EHCI controller or downstream of single/multi-TT (Transaction Translator) USB 2.0 hubs (or both) in a future operating system release.

http://support.microsoft.com/default.aspx?scid=kb;en-us;822603

Note too that the USB device drivers have been redone several times since Service Pack 1, and only rarely have been made available in Windows Update as a pushed change. You would have to compare the specific file versions of the USB controller drivers to get a handle on your issue of why the reporting is different between the machines.

The best answer: do not trust the bandwidth reporting. There is an OS cap at 80% of free CPU cycles for utilization of any USB host controller.