USB structureTime of issue : 2020- 12-16
Each USB has only one host, which includes the following layers:
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.
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.
USB power outputTime of issue : 2020- 12-16
The new USB power output specification has been developed in parallel with USB 3.1 to meet growing consumer demand. With this new specification, the power that a compatible host can provide to the device has increased from 4.5W per port to 100W. The USB power output standard includes a new PD-aware cable that can be used for "handshaking" between the host and the device. After powering on the device, you can request up to 20V x 5A power from the host. The cable needs to be checked first to ensure that it can be rated and safely output the requested power, and then the host can output more than 5v x 900mA. If the cable is confirmed to support higher power, the host will provide higher power. Ports that support USB power output and have a voltage greater than 5V or current greater than 1.5A may be marked with the USB power output logo. Like the Type-C connector, USB power output is not included in the USB 3.1 specification.
USB bus standardTime of issue : 2020- 12-16
The main experience of USB's bus standards: USB1.1-supports low-speed (HalfSpeed) 1.5Mbps and full-speed (FullSpeed) 12Mbps; USB2.0-supports high-speed (High Speed) 480Mbps; USB3.0- Supports 5Gbps at SuperSpeed. The essence of the continuous improvement of standards is the increase of signal transmission rate. The requirements for signal quality of such high-speed transmission rate are also rising. How to ensure signal quality in complicated circuit boards is the top priority in USB design.
What are the types of USB connectors?Time of issue : 2020- 12-16
With the rapid development of science and technology, many high-precision electronic devices cannot do without a good USB interface. Different USB interfaces have different transmission speeds. For example, computers, mobile phones, etc., according to the technical level, the required data transmission speed is different. In theory, the transmission speed of USB1.1 can reach 12Mbps/sec, while the speed of USB2.0 can reach 480Mbps/sec, and it can be backward compatible with USB1.1. The USB3.0 transfer rate is about 3.2Gbps (ie 320MB/S). The theoretical high rate is 5.0Gbps (that is, 500MB/S). Therefore, between the interface selection, we need to focus on consideration.