Beyond USB Packet Arrival: Frame-Identified Time Transfer to macOS

Overview

The revised study traces BLE-derived time through captured USB frame boundaries, host Mach time and a private user-level chrony clock on Apple silicon. It separates causal USB prediction, chrony’s internal estimator and delivered-clock agreement rather than treating them as one accuracy figure.

What this paper covers

• Why captured frame boundaries carry a different timing reference from packet arrival.
• How the clock feed retains source identity, mapping scope and original expiry.
• What the settled window, startup interval and withheld comparisons each reveal.

Research scope

The final 300.065-second run reports 23–339 ns settled estimator RMS, 414 ns shared-source agreement and 328 ns causal USB prediction. Shared-source agreement is not independent UTC accuracy. Startup, withheld observations and calibration limits remain part of the result.

Read it in context

Start with the macOS findings for the measurement definitions and captured instrument views. Read this revised edition for the final chrony experiment; retain the earlier 600-second paper as a distinct study. The experimental client leaves the system clock unchanged.