v0.20.0 -- Full s3 event parse and PDF creation. #28
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# Histogram body codec — IN PROGRESS (started 2026-05-20)
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Working notes for the Series III histogram-mode event body codec
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reverse-engineering effort. Mirrors the structure of
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`waveform_codec_re_status.md` (the now-completed waveform codec). The
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historical context lives in `docs/instantel_protocol_reference.md
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§7.6.2`; this doc is the active scratchpad.
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## TL;DR (current state)
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**Block framing is solved. Sample-to-channel mapping is open.**
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| Component | Status |
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|---|---|
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| 32-byte block structure | ✅ confirmed |
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| Block count vs interval count | ✅ confirmed (1 block per interval) |
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| Sample-0 = Tran_peak at 0.0005 in/s/count scale | ✅ confirmed against one event |
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| Remaining samples 1-8 → channel mapping | ❌ open |
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| Frequency encoding (TXT shows `>100 Hz`, binary shows `1`) | ❌ open |
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| Mic dB encoding | ❌ open |
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The §7.6.2 spec was less complete than its `✅ CONFIRMED` badge
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implied — the structural framing matches, but per-sample semantics
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need more cross-event analysis.
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## Confirmed structure (2026-05-20)
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### Body layout
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```
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body = [stream of 32-byte blocks]
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```
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Body length isn't always a multiple of 32 — observed 1-byte and
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9-byte trailing remnants. Walker should iterate 32-stride and stop
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before the tail.
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### 32-byte block header
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```
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[0] 0x00 always-zero (probably a fixed format tag)
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[1] segment_id (uint8) 0x00, 0x01, 0x02, 0x03 — 256 blocks per segment
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[2:4] block_ctr (uint16 LE) resets each segment (0x0100, 0x0101, ...)
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[4:22] 9× int16 LE samples
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[22:24] 0x00 0x00 constant
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[24:28] 4-byte variable unknown — possibly timestamp delta or CRC
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[28:30] 0x1e 0x0a constant signature (`30, 10`)
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[30:32] 0x00 0x00 constant
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```
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Anchor for finding data blocks during a body walk: `block[22:24] ==
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b"\x00\x00"` AND `block[28:32] == b"\x1e\x0a\x00\x00"`. The
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constant signature at byte 28-31 is the most reliable distinguisher
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from any other 32-byte content in the file.
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### Block count = interval count
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Confirmed against `example-events/histogram/N844L20G.630H`:
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- TXT reports `Number of Intervals : 792.00`
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- Binary contains 791 data blocks (one per interval, off-by-one at
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the tail — probably the last interval is truncated mid-write at
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recording stop)
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Implication: each block represents exactly one histogram interval
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(1 minute in this fixture, configurable per device). The 9 samples
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per block are the per-interval summary values BW displays in the
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TXT row for that interval.
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### What sample 0 means
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Confirmed: `sample[0] / 2000 = Tran peak amplitude in in/s` for
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the Normal-range geophone. Equivalently, sample[0] is in units of
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**0.0005 in/s per count** (NOT the 0.005 in/s display quantum or the
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1-count ADC quantum).
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Verified for block 0 of N844L20G.630H:
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- binary sample[0] = 10
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- TXT Tran_peak[0] = 0.005 in/s
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- check: 10 × 0.0005 = 0.005 ✓
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Worth verifying this holds across blocks with non-trivial Tran
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peaks before generalizing.
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## Open mappings
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### Samples 1-8 → channel + metric
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TXT structure is **10 columns per interval**:
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```
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Tran Tran Vert Vert Long Long Geo MicL MicL MicL
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Peak Freq Peak Freq Peak Freq PVS psi dB(L) Freq
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in/s Hz in/s Hz in/s Hz in/s psi dB Hz
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```
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Binary has **9 samples per block** (one short of the column count).
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None of the obvious mappings work:
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| Hypothesis | Why it fails |
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| (T_peak, T_freq, V_peak, V_freq, L_peak, L_freq, Geo, M_peak, M_freq) | Sample[1]=1 doesn't decode to `>100 Hz` under any obvious scale |
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| (T_peak, V_peak, L_peak, T_freq, V_freq, L_freq, Geo, M_peak, M_freq) | V_peak should be 1 → 0.005 in/s but is 1 → would compute 0.0005, TXT shows 0.005 for some intervals, 0.010 for others |
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| 3-per-channel (Peak, Freq, X) × T/V/L | Same scale mismatch |
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| Histogram bin counts (per-amplitude-bin) | Plausible — sample[0]=10 zeros plus tail nonzeros could be "how many samples landed in each bin during the interval". But then sample[0] = T_peak coincidence is suspicious. |
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`>100 Hz` is a sentinel BW writes when the measured zero-crossing
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frequency exceeds the geophone's measurement range. The binary
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encoding of this sentinel is unknown. Common candidates:
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- Special value (e.g. 0xFFFF / 0x7FFF / 0)
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- A flag bit in the metadata bytes (especially the 4-byte variable
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field at [24:28])
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### Metadata 4-byte variable field (bytes 24:28)
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Examples from the first 8 blocks of N844L20G.630H:
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```
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block 0: 03 90 2a 00
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block 1: 04 f2 84 00
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block 2: 03 2b e7 00
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block 3: 03 fe 11 00
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block 4: 03 f7 91 00
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block 5: 03 e9 4e 00
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block 6: 03 4c 5c 00
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block 7: 03 99 aa 00
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```
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First byte is mostly `0x03` (blocks 0,2-7) and sometimes `0x04` (block
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1). Could be a CRC, timestamp delta, or per-interval status byte.
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Worth correlating against TXT columns that vary block-to-block.
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## Fixture corpus
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In-repo histogram fixtures (paired binary + ASCII TXT):
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```
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example-events/histogram/N844L20G.630H (27 KB, 791 blocks, 792 intervals)
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example-events/histogram/N844L21H.2R0H (22 KB)
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example-events/histogram/N844L22A.VT0H (27 KB)
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example-events/histogram/N844L23B.ND0H ...
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example-events/histogram/N844L27U.U30H ...
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example-events/histogram/N844L28V.NA0H ...
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example-events/histogram/N844L6QT.IQ0H ...
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example-events/histogram/N844L6RU.BO0H ...
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example-events/histogram/N844L6SO.6I0H ...
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example-events/histogram/N844L6TP.2R0H (and more)
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```
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All from BE12844 (a single MiniMate Plus unit), recorded over
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2025-08-10 at 1-minute histogram intervals. All "noise floor"
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events — mostly silent intervals with rare spikes.
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Production has ~10,000 histogram events across many units; the
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next RE session should either pull a small variety bundle from
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prod or stick with the in-repo fixtures for initial exploration.
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## Suggested attack plan for next session
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1. **Verify sample[0] = T_peak hypothesis across all 791 blocks
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of N844L20G.630H** — confirms the scale factor isn't a coincidence.
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2. **Find a histogram event with a high-amplitude interval** so the
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sample values are non-trivial. In low-noise events almost every
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block decodes to `[10, 1, 1, 1, 1, 1, 1, 2, 2]` which gives nothing
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to disambiguate against.
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3. **Map the remaining 8 samples** by correlating block-by-block
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against the TXT columns. Especially useful: find blocks where
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exactly one channel's peak jumps — that pinpoints which sample
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slot corresponds to that channel.
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4. **Decode the `>100 Hz` sentinel** — find a block where TXT shows
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a real frequency (e.g. `73.1 Hz`) and reverse the binary value.
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5. **Investigate the 4-byte variable metadata** — likely contains
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the per-interval timestamp or some Mic-related value not in the
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9 samples.
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6. **Wire into `read_blastware_file()`** alongside the waveform
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codec (try waveform first, fall back to histogram on `00 02 00`
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preamble missing).
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7. **Update `scripts/backfill_sidecars.py`** to remove the
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`has_samples` short-circuit so histogram `.h5` files regenerate
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too.
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## Code seam for the eventual decoder
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`minimateplus/histogram_codec.py` (to-be-created) should mirror
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`minimateplus/waveform_codec.py`:
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```python
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def decode_histogram_body(body: bytes) -> Optional[dict]:
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"""Decode a histogram-mode body into per-channel sample arrays.
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Returns ``{"Tran": [...], "Vert": [...], "Long": [...], "MicL": [...]}``
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with each channel's per-interval peak values in ADC counts.
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Returns ``None`` if the body cannot be parsed.
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"""
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```
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Then in `event_file_io.read_blastware_file()`:
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```python
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decoded = decode_waveform_v2(body)
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if decoded is None:
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decoded = decode_histogram_body(body)
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if decoded is None:
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log.warning(...)
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samples = {"Tran": [], ...}
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else:
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samples = decoded_to_adc_counts(decoded)
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```
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## Related work
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- Waveform body codec — `docs/waveform_codec_re_status.md` (✅ done)
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- Protocol reference for histogram mode — `docs/instantel_protocol_reference.md §7.6.2`
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- Backfill script that consumes the decoder output — `scripts/backfill_sidecars.py`
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Reference in New Issue
Block a user