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The USB mass storage device class (also known as USB MSC or UMS) is a set of computing communications protocols, specifically a USB Device Class, defined by the USB Implementers Forum that makes a USB device accessible to a host computing device and enables file transfers between the host and the USB device. To a host, the USB device acts as an ...
USB device pulls up either D+ or D− to wake the host from the detached line state. This starts the USB enumeration process. This sets the idle state. D− pull-up D+ pull-up As full speed, then chirp in reset: Idle / J Host and device transmitter at Hi-Z. Sensing line state in case of detached state. As detached or connect state. Sync
The OTG A-device is a power supplier, and an OTG B-device is a power consumer. In the default link configuration, the A-device acts as a USB host with the B-device acting as a USB peripheral. The host and peripheral modes may be exchanged later by using Host Negotiation Protocol (HNP). The wiring for the ID pin defines the initial role of each ...
In the HID protocol, there are 2 entities: the "host" and the "device". The device is the entity that directly interacts with a human, such as a keyboard or mouse. The host communicates with the device and receives input data from the device on actions performed by the human. Output data flows from the host to the device and then to the human.
The xHCI reduces the need for periodic device polling by allowing a USB 3.0 or later device to notify the host controller when it has data available to read, and moves the management of polling USB 2.0 and 1.1 devices that use interrupt transactions from the CPU-driven USB driver to the USB host controller.
The host controller directs traffic flow to devices, so no USB device can transfer any data on the bus without an explicit request from the host controller. In USB 2.0, the host controller polls the bus for traffic, usually in a round-robin fashion.
USB 3.0 SuperSpeed – host controller (xHCI) hardware support, no software overhead for out-of-order commands; USB 2.0 High-speed – enables command queuing in USB 2.0 drives; Streams were added to the USB 3.0 SuperSpeed protocol for supporting UAS out-of-order completions USB 3.0 host controller (xHCI) provides hardware support for streams
To allow for voltage drops, the voltage at the host port, hub port, and device are specified to be at least 4.75 V, 4.4 V, and 4.35 V respectively by USB 2.0 for low-power devices, [a] but must be at least 4.75 V at all locations for high-power [b] devices (however, high-power devices are required to operate as a low-powered device so that they ...