Usb Specifications And Requirements - A Basic Guide

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USB (Universal Serial Bus) is a serial bus standard, used to connect devices with the host computer. It provides hot-pluggable Plug and Play serial interface that ensures a standard, low-cost socket for adding external peripheral devices ranging from interactive HID devices such as joysticks and pointing devices to isochronous devices such as telephony, audio, and imaging devices. USB allows integration of cascading hubs into desktop devices such as monitors and keyboards. Any device that plugs into or is connected to a USB port is considered a USB device and must comply with the requirements defined as USB requirements. USB system hardware and devices, including hubs, must comply with the Universal Serial Bus Specification, Revision 1.1.

When a system has more than one host controller, each host controller must provide full bandwidth and isochronous support. Host controllers must be located on the PCI bus to meet the requirement. The host controller providing USB 1.1 functionality must comply with the specifications for either OpenHCI (Open Host Controller Interface Specification for USB), or UHCI (Universal Host Controller ...
... Interface). Host controllers providing USB 2.0 functionality must comply with the Enhanced Host Controller Interface Specification for Universal Serial Bus 2.0.

Device and driver designs must provide maximum flexibility for interface options so that the operating system or other vendor-supplied resource management tool can coordinate user preferences, allowing multiple devices and applications simultaneously. Devices and drivers must provide multiple alternate settings for each interface where any alternate setting consumes isochronous bandwidth. The USB host controller must support wakeup capabilities from S1, S2, and S3 states. If the system contains multiple USB host controllers, all host controllers integrated on the system board are required to support wakeup from S1, S2, and S3. USB devices and USB client software and drivers must support multiple system suspend and resume cycles into and out of S3.

A USB device or driver that fits into one of the USB device class definitions must comply with the related USB device class specification. If a device vendor builds a device in a device class that does not have generic operating system driver support, or if the vendor must exploit additional, unique hardware features in their device, they can create additional WDM mini-drivers. No requirement is needed for hubs integrated into USB keyboards or into mobile systems. To minimize USB power consumption requirements, bus-powered hubs must provide ports that can be individually power switched.

A user must not be required to install software before hot-plugging a USB device. Instead, the user must be able to hot-plug the USB device and then load any software in response to operating system detection of the newly attached device. An internal device that connects to a mobile PC using USB must not continually maintain the system when all component parts are on. Such a device will override system power-management settings that control power-saving modes to protect battery life. When any USB device is connected but not active, the driver must allow system power management to suspend the mobile PC.

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