Fix SEL CWS data-frame sample misalignment (samples 1-49 read 16 bytes early)#540
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The initial CWS data frame spans 48 bytes: 16-byte common header + 8-byte nanosecond timestamp + first 24-byte sample. ParseFrame advanced only 32 (timestamp + first sample) before parsing the remaining 49 samples, omitting the common header. This read samples 1-49 of every packet 16 bytes (4 analog channels) too early, scrambling channel/sample alignment -- only the first sample of each 50-sample packet was correct -- and corrupting derived phase estimates. Advance offset/length by 48 instead of 32 so all 50 samples align and sample 49 ends exactly at the 1224-byte frame boundary. On-wire framing and the voltage-first channel order (VA,VB,VC,IA,IB,IC) were already correct.
ritchiecarroll
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clackner-gpa
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May 27, 2026
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Summary
FrameParser.ParseFrameadvanced the buffer by 32 bytes (timestamp +first sample) after the base parser handled sample 0, omitting the 16-byte
common header. Samples 1-49 of every 50-sample packet were therefore read 16
bytes (4 analog channels) too early.
[VC(prev), IA(prev), IB(prev), IC(prev), VA(cur), VB(cur)]mislabeled as[VA,VB,VC,IA,IB,IC]; only thefirst sample per packet was correct, corrupting analog values and phase
estimates.
offset/lengthby 48 (header 16 + timestamp 8 + first sample24) so all 50 samples align; sample 49 now ends exactly at the 1224-byte
frame boundary.
Root cause
base.ParseFrametakesoffsetby value and leaves the caller's offset at theframe start, so the manual loop must skip the entire initial frame (48 bytes),
not just its body (32). The bare
32literal hid the missing header.Not affected
On-wire framing and the voltage-first channel order (VA,VB,VC,IA,IB,IC,
confirmed by config-frame SignalNames) parse correctly. This was a local
offset-arithmetic defect, not a protocol/device issue.