E.2 Driver Model
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This section describes a simple fictional device and lists the steps an application takes to use the generic USB driver to control the device. This fictional device is a smart-card reader that does not conform to the smart-card device class. This reader has one interface that uses the vendor-specific class “sub class” and protocol types of 0xff.It has a bulk-in pipe, a bulk-out pipe, an interrupt pipe, and the required control pipe.
Assume that the steps necessary for the USB configuration to load a driver are complete. (How device configuration works and how to obtain the information necessary for configuration are discussed later.) With these assumptions, plug the device into the system.
Driver Actions
At this point, the generic driver has opened all the pipes for the chosen interface and is waiting for an application to assign a channel to it. The first channel assigned must be associated with the control pipe before it can be used for anything else.
The application now associates a channel to the interrupt pipe, the bulk-in pipe, and the bulk-out pipe.
The application next determines the type of pipe it has and other data about the device that it needs by using the IO$_SETCHAR and IO$_SENSECHAR functions.
The application then issues a “read” to the interrupt to determine if a card is present in the reader. If a card is present, the application uses the control pipe and the bulk in and bulk out pipes to exchange data with the smart card.