Industry information
The master controller is responsible for the transfer of data streams between the host and USB devices. These transmitted data are treated as a continuous stream of bits. Each device provides one or more interfaces that can communicate with the client program, and each interface consists of 0 or more pipes that independently transmit data between the client program and a specific terminal of the device. USBD establishes the interface and pipeline for the real needs of the host software, and when the configuration request is made, the master controller provides the service according to the parameters provided by the host software.
USB supports four basic data transmission modes: control transmission, isochronous transmission, interrupt transmission, and bulk transmission. Each transmission mode, applied to a terminal with the same name, has different properties.
Control transmission type
Supports the transmission of control, status, configuration and other information between peripherals and hosts, providing a control channel between peripherals and hosts. Each peripheral supports a control transfer type so that configuration and command/status information can be transmitted between the host and the peripheral.
Isochronous transmission type (or synchronous transmission)
Supports data transmission between peripherals and hosts with periodic, limited delay and bandwidth and constant data transfer rate. This type is error-free, so it cannot guarantee correct data transmission, and supports data transmission like computer-telephone integrated system (CTI) and audio system with the host.
Interrupt transmission type
Support input devices such as gamepads, mice and keyboards, which transmit small amounts of data between the device and the host, no periodicity, but sensitive to response time, requiring immediate response.
Bulk transmission type
Support printers, scanners, digital cameras and other peripherals, these peripherals and the host to transfer a large amount of data, USB in the case of bandwidth to meet the type of data transmission.
USB uses the block bandwidth allocation scheme. If a peripheral exceeds the current bandwidth allocation or potential requirements, the device cannot be accessed. Terminals of the synchronous and interrupt transmission types retain bandwidth and ensure that data is transmitted at a certain rate. The central and control terminal transmits transmission data at the best bandwidth available.