Wind River Glossary

Wind River Technical Glossary

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UDP, which stands for User Datagram Protocol, is a relatively fast and connectionless protocol that runs at the transport layer on top of IP networks. Because it has very few error recovery services (unlike TCP), it is used primarily for broadcasting messages and for other applications that do not require a connection. See also datagramprotocol, and transport layer.



A silicon unit that contains a single CPU.

Universal Host Controller Interface


The Universal Host Controller Interface (UHCI) is the host controller compliant with the USB 1.1 specification.

Universal Serial Bus Driver


The Universal Serial Bus Driver (USBD) is the host resident software entity responsible for providing common services to clients that are manipulating one or more functions on one or more host controllers. It is a hardware-independent software layer that implements USB Protocol 2.0. It acts as a channel between the class drivers and host controller driver. For details, refer to 3.2 Architecture Overview.



From the perspective of a device, upstream refers to a point closer to the CPU on the bus hierarchy. See also parent.

USB Device


USB device is a hardware device that performs a useful end-user function. Interactions with USB devices flow from the applications through the software and hardware layers to the USB devices.

USB Request Block


The USB Request Block (URB) is used to send or receive data to or from a specific USB endpoint on a specific USB device in an asynchronous manner.

user mode


When in user mode, the debugger is focused on user applications and processes. When a process is suspended, other processes continue to run. Compare with system mode. For Linux 2.6 and higher kernels, user mode is a separate connection type. Compare to kernel mode.

user-defined build


Project builds for which you set up and maintain your own build system and Makefiles, and for which Workbench provides minimal support beyond a GUI launch, make rules expressed in the Project Explorer, and build output to the Build Console.