Find the real speed limit: FPGA CAD for chip-specific application delay measurement
Bibliographic record
Abstract
Process variation is increasing with each successive technology node, and it has reached the point where the worst-case timing modelling employed by current FPGA CAD tools is significantly underutilizing the available silicon. Previous studies have proposed exploiting FPGA reconfigurability to reduce this underutilization using techniques such as late binding and dynamic voltage scaling. Most of the proposed solutions require the ability to measure the target application's delay on each configured chip. To accurately measure the delay of an application on a certain chip, we must measure the delay of its speed limiting paths on this specific chip. In this paper, we present a variation-aware CAD tool that automatically generates calibration bitstreams to measure the delay of any input application. Our tool identifies the statistically critical paths of the circuit and optimally selects which paths to test such that it minimizes the chances of reporting an optimistic delay, under a constraint on the number of allowed calibration bitstreams. Experimental results across a suite of benchmarks show that with one calibration bitstream we achieve 16× lower probability of reporting an optimistic delay compared to a greedy approach. With three calibration bitstreams, we reduce the probability of optimism to two chips in a million, approximately 6,000 × lower than a greedy approach.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".