The hierarchical structure of the bus architecture of the USB connector
Time：2020-10-31
A typical USB connector application system consists of a USB host, a USB device and a USB cable. In the USB bus system, external devices are generally unified as USB devices, which mainly complete specific functions, such as commonly used U disks, mobile hard disks, mice, keyboards, and game handles. The USB host is the master of the system, responsible for the control and processing of data in the USB communication process. In the USB connector transmission process, the data transmission sent by the USB host to the USB device is called Down Stream communication, and the data transmission sent by the USB device to the USB host is called UpStream communication.
Similar to the hierarchical structure design of Ethernet, the bus system of the USB connector also has a clear hierarchical structure. That is, a complete USB application system can be divided into a functional layer, a device layer, and a bus interface layer.
1. Functional layer. The functional layer is mainly responsible for the data transmission between the USB host and the device in the USB connector application system, and is composed of the functional unit of the USB device and the corresponding USB host program. The functional layer specifies the type of data transmission, which is divided into the following four types: Control Transfer, Bulk Transfer, Interrupt Transfer, and Isochronous Transfer.
2. Equipment layer. The device layer is responsible for managing USB devices, assigning addresses of USB devices, and obtaining device descriptors in the USB connector system. The work of the device layer requires the support of drivers, USB devices and USB hosts. In the device layer, the USB driver can obtain the capabilities of the USB device.
3. The bus interface layer. The bus interface layer realizes the timing of USB data transmission in the USB connector system. USB bus data transmission uses NRZI encoding, which is a reverse non-return-to-zero encoding. In the USB connector bus interface layer, the USB controller automatically performs NRZI encoding or decoding to complete the data transmission process. The bus interface layer is generally completed automatically by the USB interface hardware.
Similar to the hierarchical structure design of Ethernet, the bus system of the USB connector also has a clear hierarchical structure. That is, a complete USB application system can be divided into a functional layer, a device layer, and a bus interface layer.
1. Functional layer. The functional layer is mainly responsible for the data transmission between the USB host and the device in the USB connector application system, and is composed of the functional unit of the USB device and the corresponding USB host program. The functional layer specifies the type of data transmission, which is divided into the following four types: Control Transfer, Bulk Transfer, Interrupt Transfer, and Isochronous Transfer.
2. Equipment layer. The device layer is responsible for managing USB devices, assigning addresses of USB devices, and obtaining device descriptors in the USB connector system. The work of the device layer requires the support of drivers, USB devices and USB hosts. In the device layer, the USB driver can obtain the capabilities of the USB device.
3. The bus interface layer. The bus interface layer realizes the timing of USB data transmission in the USB connector system. USB bus data transmission uses NRZI encoding, which is a reverse non-return-to-zero encoding. In the USB connector bus interface layer, the USB controller automatically performs NRZI encoding or decoding to complete the data transmission process. The bus interface layer is generally completed automatically by the USB interface hardware.
