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All three stashes distilled into docs and dropped: xdp.md carries the AF_XDP record (ixgbe's 3 KB single-buffer XDP cap excludes the locked jumbo mix; XSK need_wakeup TX as the spin-free flow control, zero-copy-or-die, the stray-RX fill-ring trap, BTF-resolved stamp kfunc, wire-weighted size schedule as an unadopted option); connectx-5 README gains the PCICONF/ICMD/MCIA gateway constants so a rebuild needs no mstflint re-mine; e810 keeps the read-side transport map (cage-cache, bus=port, bus-5 phantom, 16-bit-addr hazard, latency as wire-truth) and NVM rollback pointers; x710 the >=30 ms EEPROM write pacing; fibergaga the empirical vendor-space finds; fs the inert-I2C-surface map; state.md stash section now empty

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flamingcow
2026-08-19 14:42:13 -07:00
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docs/modules/fibergaga/README.md
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@@ -15,6 +15,22 @@ The documented oracle — and only that: the part's 30 m reach limit makes it un
| 1E.C880–C883 | Reflection impedance/magnitude |
| PMA 1.133–1.140, PCS 3.32/3.33 | Standard set ([../README.md](../README.md)), proven live |
## Vendor space found empirically (beyond the documented set)
From a 544-register sweep of the vendor regions plus snapshot-diffing to separate live counters from static state (staleness ruled out: 20/20 interleaved known-value reads correct). The method transfers to any undocumented map — sweep for nonzero, then diff snapshots across time and across link events:
| Register | Behaviour |
|---|---|
| 1E.C886 | Link uptime, monotonic +1 per second |
| 1E.C869 | ~452 Hz free-running clear-on-read tick — **not errors**: returned an identical count on consecutive fixed-length samples, deterministic where errors would be Poisson |
| 1E.C860–C868 | MDIO write shadow log — echoes devad/register/value of the last write |
| 1E.C820/C821 | Die temperature (~97 °C on bench) and its valid bit |
| 3.C820, 3.E810, 3.E812 | Spike during link training, quiet on a settled link |
Live behaviour of the documented 3.E820 (post-FEC uncorrected frames): reads 0 on a settled link, ~1852 within 0.7 s of a retrain — LDPC coding gain keeps it at exactly zero anywhere short of the margin cliff, so it moves during training and near failure, nothing in between.
Two negative results worth keeping: short-reach mode (PMA 1.131 bit 0) lowers *our* launch power, which degrades the far end's receive, not our own SNR — useless for self-degradation; and per-pair margins are retrain-dependent on this module too (the same cable trained to 66/45/56/48 and 52/36/45/46 in consecutive sessions) — compare within one training session only.
## 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: