USB : Overview    USB Facts of Life  

As defined by the USB specs (and especially as implemented by Microsoft in Windows), it’s not easy to change the device from one Configuration to another. There is no Microsoft API that a regular user-mode program can call to tell a USB device to change to a different Configuration: this must be done from a device driver.

In practice, the situation is even worse. According to well known author and device driver expert Walter Oney, Microsoft hasn’t even been able to get its own Windows USB code to work properly with devices having multiple Configurations. In the Second Edition of his book Programming the Microsoft Windows Driver Model, he says:

“Microsoft drivers invariably work with just the first configuration of a device. The Microsoft support for composite devices won’t engage if the device has multiple configurations. Consequently, multiconfiguration devices seem to be rare in practice, and Microsoft discourages people from designing new ones.”


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