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Add a -rtc <n> flag that measures the drift of the Notecard's real-time
clock against the host computer's clock, emitting one line per second for
<n> seconds:
<n> rtc: avgDriftMsPerSecond:<rate> driftSecsPerDay:<projected>
Each second the host clock is sampled alongside the Notecard's clock via
card.time with "now":true, which reports the time as a floating-point
<epoch-seconds>.<microseconds> value.
To keep the reported figures stable rather than dominated by per-sample
USB/serial latency jitter, two techniques are used:
- Minimum round-trip filtering: each sample takes several rapid reads
and keeps the one with the lowest host round-trip time, using the
round-trip midpoint as the aligned host timestamp.
- Least-squares regression: instead of deriving the rate from just the
baseline and the current sample, the drift (microseconds of drift
since start) is regressed against host-elapsed time across every
sample collected so far. The slope is the drift rate, so per-sample
noise averages out and both reported figures converge as the run
lengthens. Regressing the drift residual directly avoids the
catastrophic cancellation of computing a slope near 1.0 and
subtracting 1.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Add a -rtc flag that measures the drift of the Notecard's real-time clock against the host computer's clock, emitting one line per second for seconds:
rtc: avgDriftMsPerSecond: driftSecsPerDay:
Each second the host clock is sampled alongside the Notecard's clock via card.time with "now":true, which reports the time as a floating-point . value.
To keep the reported figures stable rather than dominated by per-sample USB/serial latency jitter, two techniques are used:
Minimum round-trip filtering: each sample takes several rapid reads and keeps the one with the lowest host round-trip time, using the round-trip midpoint as the aligned host timestamp.
Least-squares regression: instead of deriving the rate from just the baseline and the current sample, the drift (microseconds of drift since start) is regressed against host-elapsed time across every sample collected so far. The slope is the drift rate, so per-sample noise averages out and both reported figures converge as the run lengthens. Regressing the drift residual directly avoids the catastrophic cancellation of computing a slope near 1.0 and subtracting 1.