cabletest/docs/modules/fibergaga/README.md

# Fibergaga SFP-10G-T-30M (Aquantia AQR)

The documented oracle — and only that: the part's 30 m reach limit makes it unusable in the test set, so its registers matter as reference/instrument, never as product capability. RollBall module, PHY ID 0x31c31c13, proven over the i40e oracle path ([../../nics/x710/](../../nics/x710/README.md)). Its PHY family register reference is vendored in this directory (`aquantia-aqr107-aqr109-datasheet.pdf` — the AQR107-AQR109 register reference).

## Documented registers

| Registers | What |
|---|---|
| 3.E820/3.E821 | PCS Receive Vendor **Uncorrected** Frame Counter (post-FEC) |
| 3.E840–3.E84E | Corrected Frame N Iteration Counters, N = 1…10 LDPC iterations — the pre-FEC leading indicator |
| 3.E816 | RS Corrected Error Frame Counter (system-side, secondary) |
| 1E.C884 bits 7:0 | **Estimated cable length in meters, ±1 m**, RO, from the cable diagnostic engine |
| 1E.C800 | Per-pair TDR fault verdicts (open/short/mismatch/cross-pair) |
| 1E.C801–C807 | Distances of the four worst reflections per pair, ±1 m |
| 1E.C880–C883 | Reflection impedance/magnitude |
| PMA 1.133–1.140, PCS 3.32/3.33 | Standard set ([../README.md](../README.md)), proven live |

## Pre-FEC correlation run (verification, not classification)

`3.E820` is post-FEC; the pre-FEC counters are the corrected-by-iteration histogram (3.E840–E84E). The correlation run verifies the expected ordering; this module is its instrument. Design points:

- Dose axis = *measured* SNR margin (1.133–6), not the noise-knob position — plot counter rates against margin; don't assume the knob is monotonic.
- Run at high line utilization: an uncorrected LDPC frame landing in idle/IFG leaves no host-visible trace; low-load runs undercount the host side.
- Expected ordering as margin falls: corrected-iteration counters shift toward higher N first (host still perfect — the leading-indicator regime), then E820 + PCS 3.32/33 errored blocks + host CRC/loss together. One uncorrected LDPC frame is 2048 line bits (~320 ns) and can clip multiple packets — expect burstiness, not 1:1.
- Log fast retrains alongside (IEEE 1.147) to separate FEC exhaustion from retrain hiccups.
- Clear-on-read discipline: exactly one reader during a run.
- Scope: documents the Aquantia oracle — fine; proving the pipeline is the oracle's job. The CUX3610 is Alaska-M with its own map and stays out until documented.