Self-diagnosis in Network-on-Chips

Network-on-Chips (NoCs) constitute a message-passing infrastructure and can fulfil communication requirements of the today’s System-on-Chips (SoCs), which integrate numerous semiconductor Intellectual Property (IP) blocks into a single die. As the NoC is responsible for data transport among IPs, its reliability is very important regarding the reliability of the entire system. In deep nanoscale technologies, transient and permanent failures of transistors and wires are caused by variety of effects. Such failures may occur in the NoC as well, disrupting its normal operation. An NoC comprises a large number of switches that form a structure spanning across the chip. Inherent redundancy of the NoC provides multiple paths for communication among IPs. Graceful degradation is the property of tolerating a component’s failure in a system at the cost of limited functionality or performance. In NoCs, when a switch in the path is faulty, alternative paths can be used to connect IPs, keeping the SoC functional. To this purpose, a fault detection mechanism is needed to identify the faulty switch and a fault tolerant routing should bypass it. As each NoC switch consists of a number of ports and multiple routing paths, graceful degradation can be considered even in a rather granular way. The fault may destroy some routing paths inside the switch, leaving the rest non-faulty. Thus, instead of disabling the faulty switch completely, its fault-free parts can be used for message passing. In this way, the chance of disconnecting the IP cores is reduced and the probability of having disjoint networks decreases. This study pursues efficient self-test and diagnosis approaches for both manufacturing and in-field testing aiming at graceful degradation of defective NoCs. The approaches here identify the location of defective components in the network rather than providing only a go/no-go test response. Conventionally, structural test approaches like scan-design have been employed for testing the NoC products. Structural testing