codec-re: channel rotation CONFIRMED — full multi-channel decoder works
The segment-channel scoring analyzer (from scratch/next_experiment_skeleton.py) ran and immediately confirmed the rotation hypothesis: SP0 seg 0: best fit Vert 508/508 ✓ SP0 seg 1: best fit Long 508/508 ✓ SP0 seg 3: best fit Tran 508/508 ✓ (Tran continuation) SP0 seg 5: best fit Long 508/508 ✓ SP0 seg 9: best fit Long 508/508 ✓ V70 seg 0: best fit Vert 508/508 ✓ V70 seg 1: best fit Long 508/508 ✓ Channels rotate Tran → Vert → Long → MicL per 40 02 segment header. Also discovered the segment header has DOUBLE duty: bytes [14:18] anchor the NEW segment's channel (2 samples as int16 BE in 16-count units), AND bytes [0:4] extend the PREVIOUS channel by 2 more samples (2 deltas as int16 BE). This is the same "2 anchors + delta stream" structure as the body preamble for Tran. decode_waveform_v2 now returns full per-channel sample dicts. Byte-exact verified ranges: V70: Tran 512, Vert 512, Long 512 (all first segments) JQ0: Tran 512, Vert 258 SP0: Long 1536 (all 3 L segments) Still open: the 30 NN block format (high-amplitude packed deltas) — appears mid-segment when single-byte deltas can't carry the magnitude. 6 new tests bring the count to 46. All passing.
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Claude
@@ -350,17 +350,94 @@ def decode_waveform_v2(body: bytes) -> Optional[dict]:
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"""
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Decode the body into per-channel sample arrays.
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Returns ``None`` because the full multi-channel decoder is not yet
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wired up. Tran is partially solved — see :func:`decode_tran_initial`
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for the initial portion (verified against ground-truth BW exports).
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Status (2026-05-11 evening — channel-rotation hypothesis CONFIRMED):
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segments rotate channels in fixed order **Tran → Vert → Long → MicL**.
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Each channel-segment carries a 2-sample anchor pair in segment-header
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bytes [14:18] (or in the body preamble for the initial Tran segment)
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plus a stream of delta blocks for samples 2 onward.
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Status (2026-05-11):
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- Tran[0:N] correctly decoded by ``decode_tran_initial`` for the
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first N samples of every fixture (where N = 22 / 42 / 46
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depending on event).
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- Subsequent Tran samples + all Vert / Long / MicL samples: open.
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The block stream after the first data block likely interleaves
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channels with ``30 NN`` channel-switch markers, but the exact
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switching rule is still under investigation.
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Returns ``{"Tran": [...], "Vert": [...], "Long": [...], "MicL": [...]}``
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with each channel's decoded samples in 16-count units (LSB = 0.005
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in/s at Normal range). Returns ``None`` if the body cannot be
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parsed.
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"""
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return None
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if len(body) < 7 or body[0:3] != b"\x00\x02\x00":
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return None
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channels = ["Tran", "Vert", "Long", "MicL"]
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out: dict = {ch: [] for ch in channels}
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# Initial Tran segment: preamble anchor pair + delta blocks before first 40 02.
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t0 = int.from_bytes(body[3:5], "big", signed=True)
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t1 = int.from_bytes(body[5:7], "big", signed=True)
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out["Tran"].extend([t0, t1])
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start = find_data_start(body)
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if start < 0:
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return out
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blocks = walk_body(body, start)
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seg_idx = [i for i, b in enumerate(blocks) if b.tag_hi == 0x40]
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def apply_blocks(channel: str, anchor: int,
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block_start: int, block_end: int) -> int:
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"""Apply delta blocks [block_start, block_end) to *channel*'s sample
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list, starting from *anchor*. Returns the final cumulative value."""
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cur = anchor
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for bi in range(block_start, block_end):
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blk = blocks[bi]
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if blk.tag_hi == 0x10:
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for byte in blk.data:
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for nib in ((byte >> 4) & 0xF, byte & 0xF):
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cur += _s4(nib)
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out[channel].append(cur)
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elif blk.tag_hi == 0x20:
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for byte in blk.data:
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cur += _i8(byte)
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out[channel].append(cur)
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elif blk.tag_hi == 0x00:
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for _ in range(blk.tag_lo):
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out[channel].append(cur)
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# 30 NN: unknown content; skip.
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# 40 02: should not occur in segment data.
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return cur
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# Initial Tran segment: deltas from start of body up to first 40 02 (or end).
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first_seg = seg_idx[0] if seg_idx else len(blocks)
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last_tran_value = apply_blocks("Tran", t1, 0, first_seg)
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# Subsequent segments rotate channels. Each segment header carries:
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# bytes [0:2] and [2:4] = 2 deltas extending the PREVIOUS channel
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# bytes [14:16] and [16:18] = anchor pair for THIS segment's channel
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#
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# Rotation: V, L, M, T, V, L, M, T, ... (initial Tran segment is the
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# implicit T in the cycle.)
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rotation = ["Vert", "Long", "MicL", "Tran"]
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# Track each channel's "running cumulative value" so we can apply the
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# previous-channel extension deltas at every segment boundary.
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last_value = {"Tran": last_tran_value, "Vert": None, "Long": None, "MicL": None}
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for k, hi in enumerate(seg_idx):
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channel = rotation[k % 4]
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prev_channel = "Tran" if k == 0 else rotation[(k - 1) % 4]
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header = blocks[hi]
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if len(header.data) < 18:
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continue
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# Extend the PREVIOUS channel by 2 more samples (deltas in bytes [0:4]).
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prev_d0 = int.from_bytes(header.data[0:2], "big", signed=True)
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prev_d1 = int.from_bytes(header.data[2:4], "big", signed=True)
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if last_value[prev_channel] is not None:
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v = last_value[prev_channel] + prev_d0
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out[prev_channel].append(v)
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v += prev_d1
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out[prev_channel].append(v)
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last_value[prev_channel] = v
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# Anchor pair for THIS segment's channel.
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c0 = int.from_bytes(header.data[14:16], "big", signed=True)
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c1 = int.from_bytes(header.data[16:18], "big", signed=True)
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out[channel].extend([c0, c1])
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# Apply delta blocks for this segment.
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next_hi = seg_idx[k + 1] if k + 1 < len(seg_idx) else len(blocks)
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last_value[channel] = apply_blocks(channel, c1, hi + 1, next_hi)
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return out
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