University of Michigan Advanced Computer Architecture Lab. March 21, Key PED Challenges David Blaauw University of Michigan

University of Michigan Advanced Computer Architecture Lab. March 21, Run Time Leakage The Last Leakage Frontier…. Current approaches: Sleep mode: MTCMOS, ABB, State assignment Sub-critical paths: Dual Vt, Vdd address Variable workload: DVS / ABB Performance critical gates will become increasingly dominant Critical paths, buss / interconnect drivers, clock nets Large gate sizes, low-Vt, high-Vdd assignment Low switching activity…. Need for detailed leakage map of SOC designs

University of Michigan Advanced Computer Architecture Lab. March 21, Variability Exponential dependence of subthreshold leakage on Vt Super exponential dependence of gate leakage on oxide thickness Significant increase in variability expected Statistical modeling of power and energy Few bad regions on chip will dominate Likelihood of uniformly good silicon is diminishing Self tuning / adjusting silicon and circuits

University of Michigan Advanced Computer Architecture Lab. March 21, Sub-Critical Operation Digital mind set has been to guarantee correct operation under all circumstances Coupling noise, supply integrity, SEU, inter- and intra-die variability Loss of predictability Increasing margins Inverse correlation between severity and likelihood Most sever failures also least common Gradual failure behavior Statistical analysis of failure behavior Architectural / system level correction mechanism Power robustness trade-off