ForEVeR

Abstract

As silicon technology scales, modern processor and embedded systems are rapidly shifting towards complex chip multi-processor (CMP) and system-on-chip (SoC) designs. As a side effect of complexity of these designs, ensuring their correctness has become increasingly problematic. Within these domains, Network-on-Chips (NoCs) are a de-facto choice to implement on-chip interconnect; their design is quickly becoming extremely complex in order to keep up with communication performance demands. As a result, design errors in the NoC may go undetected and escape into the final silicon. In this work, we propose ForEVeR, a solution that complements the use of formal methods and runtime verification to ensure functional correctness in NoCs. Formal verification, due to its scalability limitations, is used to verify smaller modules, such as individual router components. To deliver correctness guarantees for the complete network, we propose a network-level detection and recovery solution that monitors the traffic in the NoC and protects it against escaped functional bugs. To this end, ForEVeR augments the baseline NoC with a lightweight checker network that alerts destination nodes of incoming packets ahead of time. If a bug is detected, flagged by missed packet arrivals, our recovery mechanism delivers the in-flight data safely to the intended destination via the checker network. ForEVeR's experimental evaluation shows that it can recover from NoC design errors at only 4.9% area cost for an 8x8 mesh interconnect, over a time interval ranging from 0.5K to 30K cycles per recovery event, and it incurs no performance overhead in the absence of errors. ForEVeR can also protect NoC operations against soft-errors: a growing concern with the scaling of silicon. ForEVeR leverages the same monitoring hardware to detect soft-error manifestations, in addition to design-errors. Recovery of the soft-error affected packets is guaranteed by building resiliency features into our checker network. ForEVeR incurs minimal performance penalty up to a flit error rate of 0.01% in lightly loaded networks.