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Force master/slave roles at bringup (A master / B slave, IEEE 7.32): the AN role lottery plus per-training DSP convergence moves per-pair SNR up to ~3.6 dB, so sessions are pinned to identical conditions; launch power documented firmware-pinned (1.130), single-training SNR documented as a weak qualification number

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flamingcow
2026-08-13 14:23:57 -07:00
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docs/modules/fs/README.md
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@@ -33,7 +33,7 @@ Protocol and full verified catalog: [bcm84891l-mdio-commands.md](bcm84891l-mdio-
| Capability | How | Observed |
|---|---|---|
| Per-pair SNR | `CMD_GET_SNR` 0x8030, **invoked bare** (writing the documented DATA1 display flag returns zeros; IEEE 1.133–1.140 never populate — constant 0x8080) | DATA2–5 = SNR A–D ×0.1 dB; ≈ 27–32 dB absolute on bench, 0.1–0.4 dB jitter. 10GBASE-T operating point ≈ 26.5 dB, so margin ≈ value − 26.5. cabletest shows the margin classified green ≥ 3 dB / amber ≥ 1 dB / red below — provisional thresholds until the graded-noise correlation run |
| Per-pair SNR | `CMD_GET_SNR` 0x8030, **invoked bare** (writing the documented DATA1 display flag returns zeros; IEEE 1.133–1.140 never populate — constant 0x8080) | DATA2–5 = SNR A–D ×0.1 dB; ≈ 27–32 dB absolute on bench, 0.1–0.4 dB jitter. 10GBASE-T operating point ≈ 26.5 dB, so margin ≈ value − 26.5. cabletest shows the margin classified green ≥ 3 dB / amber ≥ 1 dB / red below — provisional thresholds until the graded-noise correlation run. **Each training re-converges differently**: back-to-back retrains with identical roles, temperature and noise moved one pair by 3.6 dB (roles pinned, launch power pinned — the convergence itself is the variable, and the two bench modules differ in stability: ≤1.5 dB spread on one, 3.6 dB on the other). A single training's absolute SNR is a weak qualification number; qualification wants median-of-N trainings, live SNR is honest as a within-session tracker |
| Die temperature | `CMD_GET_CURRENT_TEMP` 0x8031 | ~68–70 °C on bench |
| Supply rails | `GET_CURRENT_VOLTAGE` 0x802F | 0.8 V and 1.88 V rails, tenths of mV |
| Error counters | IEEE PCS 3.32/3.33 — block lock, latched errored-block/BER, clear-on-read | The noise-stress error proxy |
@@ -52,6 +52,8 @@ Protocol and full verified catalog: [bcm84891l-mdio-commands.md](bcm84891l-mdio-
| Jumbo | 0x801C/0x801D | GET 0x801D answers in DATA1 — scratch-prone, unusable — and bringup cannot assume a cable to probe through, so cabletest forces enable every boot (SET 0x801C + AN restart); the running mix's 9018-byte frames are the standing wire truth (`phy.go`). The FS at its 9K option passes them at line rate with zero loss/corrupt |
| 1588 | 0x8004 | Disabled (engine registers undocumented — see asks below) |
| Limited reach | 0x8006 | Disabled — its DATA3 "linked in LR mode" bit, the only handler-visible trace of the DSP length estimate, is unavailable without a config change |
| Master/slave role | IEEE 7.32 bits 15/14 | Left to AN the resolution is a per-training lottery; manual config writes stick exactly and the resolution follows deterministically (7.33.14, no config fault with complementary ends). cabletest forces A master / B slave every boot (`phy.go`) so sessions are measured under identical conditions |
| Launch power | IEEE 1.130, 1.0.11 | 1.130 reads 0x0003 and is firmware-pinned: host writes to the short-reach bit revert instantly and the value never changes across retrains, so launch power is constant and not host-influenceable. PMA low-power bit clear. The handler catalog has no TX-power command |
## Firmware-reliability notes