Guaranteeing the quality of services in networks on chip

Users expect a predictable quality of service (Qos) of embedded systems, even for future, more dynamic, applications. System-on-chip designers use networks on chip (Noc) to solve deep submicron problems, and to divide global prob lems into local, decoupled problems. NOC5 provide services through protocol stacks, and introducing guaranteed services enables w re-use and platformbased design. It also provides globally predictable behaviour, as required by the user, when combining local, decoupled solutions. There are several levels of Q0S commitment (correctness, completion, completion bounds), with increas ing cost. A combination of guaranteed and best-effort (no commitment) services combines their respective attractive features: predictable behaviour, and good average resource utilisation. The IETHEREAL NOC is an example of this ap proach, and forms the basis of a QOS-based design style, as advocated in this chapter.