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Dissolve resolved analyses into standalone device docs; open-questions.md keeps only the four live problems; discard NIC-timestamp length path (BCM ECD is proven) and Aquantia length trivia (30m part, oracle-only)

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flamingcow
2026-08-12 21:30:16 -07:00
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docs/goals.md
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@@ -9,11 +9,8 @@ The target of measurement is the cable, not throughput. Line rate is a means to
1. **Loss and error attribution** — reception gaps, link errors, NIC/driver counters as first-class output alongside application loss. Baseline loss must be exactly zero before a run counts; any host-side loss masks real cable faults.
2. **Noise tolerance** — a deliberately-bad "noise" cable intertwined with the test cable, driven by link up/down cycling, stresses the cable under test with alien crosstalk.
3. **Per-pair SNR** from the module PHYs — the leading indicator of a marginal cable before it drops frames. IEEE 802.3an standard registers on the Marvells; the BCM leaves those unpopulated and reports through its vendor command handler instead (modules/fs/).
4. **Cable length** — sanity check and fault localization. Sources, in preference order:
- Module PHY DSP estimate — works on a linked cable.
- PHY TDR — localizes opens/shorts both-ended; healthy-cable length only single-ended.
- NIC timestamp path-delay — works linked, module-independent; needs hardware timestamps and a short-cable calibration.
5. **Pre-FEC error visibility** — corrected-error counters that move before post-FEC loss appears. Vendor-specific; located on the Aquantia (open-questions.md §5), unlocated elsewhere. Standard latched PCS counters (errored blocks, BER, block-lock loss) are the working proxy under noise stress.
4. **Cable length** — sanity check and fault localization. The BCM ECD is the product path: per-pair lengths in meters, healthy pairs included, proven meter-accurate on the bench (modules/fs/).
5. **Pre-FEC error visibility** — corrected-error counters that move before post-FEC loss appears. Vendor-specific; located on the Aquantia (modules/fibergaga/), unlocated elsewhere. Standard latched PCS counters (errored blocks, BER, block-lock loss) are the working proxy under noise stress.
## Design preferences that shaped the tool