In the context of multi-IP chips making use of internal communication paths other than the traditional buses, source synchronous links for use in multi-synchronous Networks-on-Chip (NoCs) are becoming the most vulnerable points for correct network operation and therefore need to be safeguarded against intra-link delay variations and signal misalignments. The intricacy of matching link net attributes during placement and routing and the growing role of process parameter variations in nanoscale silicon technologies, as well as the deterioration due to the ageing of the chip, are the root causes for this. This chapter addresses the challenge of designing a timing variation and layout mismatch tolerant link for synchronizer-based GALS NoCs by implementing a self-calibration mechanism. A timing variation detector senses the misalignment, due to process variation and wearout, between data lines with themselves and with the transmitter clock routed with data in source synchronous links. Then, a suitable delayed replica of the transmitter clock is selected for safe sampling of misaligned data. This chapter proves the robustness of the link in isolation with respect to a detector-less link, also addressing integration issues with the downstream synchronizer and switch architecture, proving the benefits in a realistic experimental setting for cost-effective NoCs.
