Before data can transfer, the host and device must establish a pipe. A pipe is an association between a device’s endpoint and the host controller’s software. Host software establishes a pipe with each endpoint address the host wants to communicate with.The host establishes pipes during enumeration. If a user detaches a device from the bus, the host removes the no longer needed pipes. The host can also request new pipes or remove unneeded pipes by using control transfers to request an alternate configuration or interface for a device.
Every device has a default control pipe that uses endpoint zero. The configuration information received by the host includes an endpoint descriptor for each endpoint that the device wants to use. Each endpoint descriptor contains an endpoint address, the type of transfer the endpoint supports, the maximum size of data packets, and, when appropriate, the desired interval for transfers.
Tags: Connecting, enpoints, host
