FODM: A Framework for Accurate Online Delay Measurement Supporting All Timing Paths in FPGA

Weixiong Jiang, Heng Yu, Hongtu Zhang, Yuhao Shu, Rui Li, Jian Chen, Yajun Ha

Research output: Journal PublicationArticlepeer-review

5 Citations (Scopus)


Voltage and frequency scaling (VFS) has been widely used to improve energy efficiency, lifespan, and system reliability by converting conservative timing margins into V_{text {dd}} reduction. Along these lines, to investigate the potential implementation of VFS technique in exploring the timing margins under different voltages and frequencies, in situ or online circuit delay measurement is required to monitor all timing paths, which are usually ended with terminal registers. The previously reported online delay measurement approaches require the output of a terminal register to be measurable. However, some FPGA timing paths are ended with embedded hardcores such as DSPs or BRAMs. It is impossible to measure the output of the terminal register inside a hardcore. To address the issue, we propose an online delay monitor (ODM) that can accurately measure the delay of any type of timing path in real-time conditions. The ODM is mainly composed of two shadow registers and a phase-shifted clock. The shadow registers use a phase-shifted clock signal as the input and the output signal of the combinational logic as the clock. In addition, we present an automatic tool and its corresponding design flow (FODM) for inserting an ODM to monitor a path. Compared with the state-of-the-art, our experimental results indicate that the proposed method has the ability to accurately measure the delays online for all the potential timing paths, regardless of their path termination types. Moreover, we demonstrate an average measurement error of only 1.51% using eight floating-point operators at different voltages.

Original languageEnglish
Pages (from-to)502-514
Number of pages13
JournalIEEE Transactions on Very Large Scale Integration (VLSI) Systems
Issue number4
Publication statusPublished - Apr 2022


  • Circuits and systems
  • digital circuits
  • digital integrated circuits

ASJC Scopus subject areas

  • Software
  • Hardware and Architecture
  • Electrical and Electronic Engineering


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