Round 3 of the Task 4 review. Three defects, all in FrameDecoder rule 3.
The resync backstop was one-directional. `predicted` is never below
lastEmittedEnd + dt, so rejecting a correction that would step backwards
meant only a LAGGING chain could ever be pulled back; a chain running fast
drifted ahead without bound. Two hosts' crystals differ by tens of ppm, so a
declared SamplingRate is always slightly wrong in one direction or the other
and this is certain on a long session. A leading timeline cannot be corrected
in one burst without going backwards -- lastEmittedEnd is by definition past
arrival -- so the excess is bled off by drawing each burst 10 % narrower until
the timeline is back inside the threshold.
A repeated packet counter was treated as a normal packet. The C client
de-duplicates fragments only, so an unfragmented update reaching a host that
joined the group on two interfaces was emitted twice, doubling the values and
advancing the timeline by a burst that never existed.
The samplingRate == 0 path differenced two HrtRateFit::toSeconds() results.
toSeconds() divides an absolute tick count -- ~1e11 on a producer that has
been up a day -- by a rate refitted on every packet, so its few-parts-in-1e4
wobble arrives multiplied by the whole elapsed epoch: tens of milliseconds of
jitter on a value whose consecutive difference is a few milliseconds. Raw
ticks are differenced instead, anchored on the first usable packet so the
wobble applies only to the interval since attach.
The existing hrt-gap test could not have caught the last one: its 10 ms
producer period made the expected answer exactly kDefaultDt, so a decoder
that derived nothing passed. It now uses 25 ms.
Four tests added, all sabotage-proven. The plan is updated to match.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
The fit keeps the slope and discards the intercept, so the result counts from
the producer's boot. Tasks 4 and 7 compose it with ClockOffset::map, which is
correct, but the bare name invites passing it straight to a plot axis.
Also unwrapped the stalled-clock assertion from behind `if (fit.ready())` —
that branch never runs, so the test confirmed nothing.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Adds TimeBase.h/cpp with ClockOffset (latched wall-clock offset with
one-sided recalibration on positive drift only, so early-arriving packets
do not wobble the trace) and HrtRateFit (sliding-window OLS that recovers
an unknown hrt tick rate from receive timestamps). Also adds
TimeSignalScale() which maps UDPS type codes to seconds-per-count.
9 new tests, all 28 pass.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
