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• Time of issue:2020-12-16
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(Summary description)Each USB has only one host, which includes the following layers:

Bus interface

The USB bus interface handles the interconnection between the electrical layer and the protocol layer. From the perspective of interconnection, similar bus interfaces are given by the device and the host at the same time, such as the serial interface machine (SIE). The USB bus interface is implemented by the main controller.

The USB system uses a host controller to manage the data transfer between the host and the USB device. The interface between it and the main controller depends on the hardware definition of the main controller. At the same time, the USB system is also responsible for managing USB resources, such as bandwidth and bus energy, which makes it possible for customers to access USB. The USB system also has three basic components:

The host controller driver (HCD) can map different host controller devices to the USB system. The interface between HCD and USB is called HCDI. The specific HCDI is defined by the operating system that supports different main controllers. The universal main controller driver (UHCD) is at the bottom of the soft structure, and it manages and controls the main controller. UHCD realizes the communication and control of the USB host controller, and it is hidden from other parts of the system software. The highest level in the system software communicates with the main controller through the UHCD software interface.

The USB driver (USBD) is on top of the UHCD drive, and it provides a driver-level interface to meet the requirements of existing device driver designs. USBD provides a data transmission structure in the form of I/O request packets (IRPs), which consists of the need to transmit data through specific pipes (Pipe). In addition, USBD makes the client an abstraction of the device to facilitate abstraction and management. As part of the abstraction, USBD has a default pipeline. It can access all USB devices for standard USB control. The default pipeline describes a logical channel for communication between USBD and USB devices.

Host software

In some operating systems, no USB system software is provided. The software was originally used to provide configuration information and loading structure to the device driver. In these operating systems, the device driver will use the provided interface instead of directly accessing the USBDI (USB Driver Interface) structure.

USB client software

It is located at the highest level of the software structure and is responsible for handling specific USB device drivers. The client program layer describes all the software entrances directly acting on the device. When the device is detected by the system, these client programs will directly act on the peripheral hardware. This shared feature puts the USB system software between the client and its device, which must be processed by the client program according to the device image formed by the USBD on the client.

Each layer of the host has the following functions:

Detect connected and removed USB devices.

Manage the data flow between the host and USB devices.

Connect USB status and activity statistics.

Control the electrical interface between the main controller and the USB device, including limited energy supply.

HCD provides an abstraction of the main controller and an abstraction of the main controller's perspective of data transmitted via USB. USBD provides an abstraction of USB devices and an abstraction of data transmission between USBD clients and USB functions. The USB system facilitates data transfer between customers and functions, and serves as a control point for the standardized interface of USB devices. The USB system provides buffer management capabilities and allows data transmission to be synchronized with customer and functional requirements.