Unbounded - when a condition can persist for a non-deterministic amount of time - e.g. unbounded priority inversion where the set of middle level priority interference tasks may cause the inversion to persist for an arbitrary time.
Unit Test - a test designed to validate and verify a software and/or hardware unit that is a building block for a larger system in isolation.
Utility Curve - an XY graph which shows time on the X axis between a service release and relative deadline and shows utility or damage caused to the system caused by service response generation.
Virtual Timer - a timer which is not directly supported by a hardware interval timer, but rather is a software tick counter that can generate a signal after the passing of N software ticks.
VoIP - Voice over IP, a protocol for transporting voice duplex audio over the Internet protocol.
Watchdog Timer - a hardware based interval timer which counts down (or up) and when it reaches zero (or all F’s) it generates an H-reset signal causing the system to re-boot - critical software services are expected to post keep-alives to a system sanity monitor which normally in turn resets the watchdog timer before it expires. If the software loses sanity, I.e. the sanity monitor fails to reset the watchdog timer (e.g. if a deadlock were to occur), then the idea is that the system will be able to recover by re-booting.