The Default Pipe

Each USB device has a special control endpoint called the default endpoint. Its communication channel is called the default pipe. Most, if not all, device setup is done through this pipe. Many USB devices have this pipe as their only control pipe.

The usb_get_dev_data(9F) function provides the default control pipe to the client driver. This pipe is pre-opened to accommodate any special setup needed before opening other pipes. This default control pipe is special in the following ways:

• This pipe is shared. Drivers that are operating other interfaces of the same device use the same default control pipe. The USBA 2.0 framework arbitrates this pipe among the different drivers.

• This pipe cannot be opened, closed, or reset by the client driver. This restriction exists because the pipe is shared.

• The pipe is autocleared on an exception.

Other pipes, including other control pipes, must be opened explicitly and are exclusive-open only.