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fix(protocol): update chunk counter formula to use max(key4[2:4], 0x0400) for accurate data streaming

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Brian Harrison
2026-04-26 01:28:47 -04:00
parent 7976b544ed
commit 2f084ed105
3 changed files with 56 additions and 39 deletions
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docs/instantel_protocol_reference.md
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@@ -1231,23 +1231,31 @@ Two critical differences from `build_bw_frame`:
| Frame | offset_word | counter | params | Purpose |
|---|---|---|---|---|
| Probe | `0x1004` | `0x0000` | 10 bytes (`bulk_waveform_params(0)`) | Initiate transfer |
| Chunk 1 | `0x1004` | `key4[2:4]` | 11 bytes | First data chunk |
| Chunk 2 | `0x1004` | `key4[2:4] + 0x0400` | 11 bytes | Second chunk |
| Chunk N | `0x1004` | `key4[2:4] + (N-1) * 0x0400` | 11 bytes | Nth chunk |
| Chunk 1 | `0x1004` | `max(key4[2:4], 0x0400)` | 11 bytes | First data chunk |
| Chunk 2 | `0x1004` | `max(key4[2:4], 0x0400) + 0x0400` | 11 bytes | Second chunk |
| Chunk N | `0x1004` | `max(key4[2:4], 0x0400) + (N-1) * 0x0400` | 11 bytes | Nth chunk |
| … | … | … | … | … |
| Termination | `0x005A` | `key4[2:4] + N * 0x0400` | 10 bytes | End transfer |
| Termination | `0x005A` | `max(key4[2:4], 0x0400) + N * 0x0400` | 10 bytes | End transfer |
> ⚠️ **2026-04-06 CORRECTED — chunk counter is `key4[2:4] + (N-1) * 0x0400`.**
> The 4-2-26 BW TX capture showed counter=0x1004 for chunk 1 of key `01110000`, leading to
> an interim "monotonic n * 0x0400" formula. This was accidentally correct because
> `key4[2:4] == 0x0000` for that event.
>
> **2026-04-24 FINAL CORRECTION:** The counter is an absolute circular-buffer address.
> **2026-04-24 CORRECTION:** The counter is an absolute circular-buffer address.
> BW's true formula is `key4[2:4] + (chunk_num - 1) * 0x0400` where `key4[2:4]` is the
> event's storage base offset (`(key4[2]<<8) | key4[3]`). For keys where
> `key4[2:4] != 0x0000` (e.g. key `01111884`), using `n * 0x0400` sends requests into the
> wrong buffer region — the device returns data from a completely different event and
> `b"Project:"` never appears in the stream. Confirmed correct 2026-04-24.
> wrong buffer region — the device returns data from a completely different event.
>
> **2026-04-26 FINAL CORRECTION:** The formula `key4[2:4] + (N-1) * 0x0400` is wrong when
> `key4[2:4] == 0x0000` (e.g. event key `01110000`, the very first event after a device erase).
> Counter=0x0000 for chunk 1 is the same address as the probe frame — the device re-returns
> the STRT record data instead of waveform payload (frame 1 has len=1097, same as probe, and
> contains `b"STRT\xff\xfe"`, contributing zero waveform bytes).
> Final formula: `max(key4[2:4], 0x0400) + (chunk_num - 1) * 0x0400`.
> For key `01110000`: chunk 1 = 0x0400 (confirmed working, empirical test 2026-04-06).
> For key `0111245a`: chunk 1 = 0x245a (unchanged, confirmed from 4-3-26 capture).
The `stop_after_metadata=True` flag causes the loop to stop as soon as `b"Project:"` is
found in the accumulated A5 frame data, typically after 4–9 chunks. A termination frame