GROK-LAB: generating real on-chip knowledge for intra-cluster delays using timing extraction

Abstract

Timing Extraction identifies the delay of fine-grained components within an FPGA. From these computed delays, the delay of any path can be calculated. Moreover, a comparison of the fine-grained delays allows a detailed understanding of the amount and type of process variation that exists in the FPGA. To obtain these delays, Timing Extraction measures, using only resources already available in the FPGA, the delay of a small subset of the total paths in the FPGA. We apply Timing Extraction to the Logic Array Block (LAB) on an Altera Cyclone III FPGA to obtain a view of the delay down to near individual LUT granularity, characterizing components with delays on the order of a few hundred picoseconds with a resolution of ±3.2 ps. This information reveals that the 65 nm process used has, on average, random variation of σ/µ = 4.0% with components having an average maximum spread of 83 ps. Timing Extraction also shows that as VDD decreases from 1.2 V to 0.9 V in a Cyclone IV 60 nm FPGA, paths slow down and variation increases from σ/µ = 4.3% to σ/µ 5.8%, a clear indication that lowering V_(DD) magnifies the impact of random variation.