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A USB hub is a device that expands a single Universal Serial Bus (USB) ... The root hub is the first tier, and the last devices are on the seventh tier, allowing five ...
For example, a USB 2 PCIe host controller card that presents 4 USB "Standard A" connectors typically presents one 4-port EHCI and two 2-port OHCI controllers to system software. When a high-speed USB device is attached to any of the 4 connectors, the device is managed through one of the 4 root hub ports of the EHCI controller.
During USB communication, data is transmitted as packets. Initially, all packets are sent from the host via the root hub, and possibly more hubs, to devices. Some of those packets direct a device to send some packets in reply. After the sync field, all packets are made of 8-bit bytes, transmitted least-significant bit first. The first byte is a ...
The hub built into the host controller is called the root hub. A USB device may consist of several logical sub-devices that are referred to as device functions. A composite device may provide several functions, for example, a webcam (video device function) with a built-in microphone (audio device function).
The hub may also have some non-removable functions in place of ports. A self-powered hub is a device that provides high-power ports by supplementing the power supply ...
USB4 hubs and docks are defined as their own category of USB4 devices that include further requirements. For example, a USB4 hub must also serve as a classic USB 3.2 hub with DP Alternative Mode passthrough with hosts that do not support USB4 connections. See USB4 capabilities by device type for more details.
Open Host Controller Interface (OHCI) [1] is an open standard.. Die shot of a VIA VT6307 Integrated Host Controller used for IEEE 1394A communication. When applied to an IEEE 1394 (also known as FireWire; i.LINK or Lynx) card, OHCI means that the card supports a standard interface to the PC and can be used by the OHCI IEEE 1394 drivers that come with all modern operating systems.
A USB compound device contains an embedded USB hub and one or more non-removable USB devices. [1] It may or may not have exposed downstream ports. The internal USB hub may be a physical IC that connects to other ICs, or the hub and all functions may be implemented in software on a single IC (though it is more common to integrate them as a composite device in this case).