SNUADC sends no time; the recorder stamps by count¶

The SNUADC board streams samples with no time stamps. Every SNUADC time in VitalDB is the recorder's model of the board's clock: the sample count at the nominal rate, pulled back when it drifts too far.


Status	established: shown on many cases, with a control.
Clocks	SNUADC sample clock, Recorder PC clock
Devices	SNUADC, Vital Recorder
Variables	ECG lead II (SNUADC), Arterial pressure (SNUADC), Plethysmogram (SNUADC)

What it means¶

Anything the board loses without telling the recorder (a stall, a pause) is invisible in the stamps. The stamp sawtooth is the recorder correcting its model, not the board.

What is done about it¶

The stamp model refits the line; paced and continuity checks find what the stamps miss.

Evidence¶

Study	Date	Status	Summary
The SNUADC firmware	2026-10-13	current	The public SNUADC firmware explains the board's timing: it sends no time stamps, samples on its 16 MHz crystal, loses time rather than bunching samples after a stall, reads its channels one after another, and truncates its values. A predicted fault at the microsecond counter's wrap was not found in the data.
The stamp sawtooth model for SNUADC and BIS	2026-10-12	current	Fitting each track's record stamps against its sample count as a drift with corrections (a sawtooth) puts SNUADC and BIS on one timeline without any artefact. Checked against shared bursts, the EEG–ECG timing error falls from about 790 ms on the recorded stamps to 33 ms with one constant per SNUADC mode in the pilot, and 42 ms over the whole release.
Clock corrections in every file	2026-10-11	current	A scan of all 6,388 files for the jumps where the recorder re-synchronises a device's stamps. Each device type has its own correction signature; only SNUADC and BIS correct clearly enough to measure their drift.