EMEP: Early-Monitoring Error Prediction for Activity and Variability Resilience in a 28-nm RISC-V Controller

In situ timing monitoring significantly improves the energy efficiency of low-voltage digital ICs by eliminating the excessive timing margins inserted to address high PVT variations in conventional digital flows. However, such techniques face challenges related to design overhead and robustness. This article presents the early-monitoring error prediction (EMEP) technique to address these issues effectively. With minimal clock tree (CT) impact and low area (1.6%) and power overhead (2%), EMEP achieves 60% endpoint coverage. This wide coverage, combined with increased resilience against critical activity masking and variability, enhances system robustness. In addition, 4σ yield is ensured through statistical critical path identification. Automatically integrated into a 28-nm CMOS RISC-V microcontroller, EMEP recovers 86% of conventional energy margins and reduces energy consumption by 2.9 pJ/cycle (41%), outperforming traditional replicas by 61% and endpoint monitoring (EPM) techniques by 31%. EMEP operates the microcontroller with only 14.5% energy overhead compared with margin-free operation, which is essential to address activity uncertainty, becoming minimal when the slowest critical paths are active.