theater/cabletest
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

BCM ECD recovered from OpenBCM SDK and proven: 1E.4006 start, 1.A896 verdicts, 1.A897-9A per-pair meters -- meter-accurate on a 45m cable, healthy pairs report length

Browse Source
This commit is contained in:
flamingcow
2026-08-12 19:37:54 -07:00
parent c57816345f
commit ad9bc9fae4
3 changed files with 24 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files
docs/open-questions.md
+5 -6
View File
@@ -61,17 +61,16 @@ The path crosses two 10GBASE-T PHYs (~2–3 µs pipeline each); the timestamp le
## 3. Cable-length strategy
**Status: consolidated — PHY features are the product path, NIC timestamps the fallback.**
**Status: consolidated — PHY features are the product path, NIC timestamps the fallback. The BCM path works.**
| Path | Status |
|---|---|
| BCM ECD/DSP | Real, but the ECD chapter is missing from FS's docs (modules/fs/ ask list). The handler exposes only a 1-bit trace of the DSP estimate (limited-reach linked bit, and only with LR mode enabled) |
| Aquantia DSP/TDR (oracle only) | **Fully documented**: `1E.C884` length ±1 m, per-pair TDR verdicts and reflection distances (modules/fibergaga/). Proves at least one vendor exposes DSP length in a plain register — precedent for the FS ask |
| Marvell VCT (Wiiteks) | Undocumented and gated behind the brick trap; sacrificial-unit-only single-shot templates (modules/wiitek/) |
| BCM ECD | **Working on the bench** — recipe recovered from the OpenBCM SDK (`phy8481.c` cable-diag, same register family as the 84891L's command handler) and validated: per-pair verdicts + per-pair lengths in meters on a plugged healthy cable. Calibration and run-disturbance characterization remain (modules/fs/) |
| Aquantia DSP/TDR (oracle only) | **Fully documented**: `1E.C884` length ±1 m, per-pair TDR verdicts and reflection distances (modules/fibergaga/) |
| Marvell VCT (Wiiteks) | Undocumented and gated behind the brick trap; sacrificial-unit-only single-shot templates (modules/wiitek/). The BCM ECD result layout (verdict nibbles + per-pair length registers) is a fresh analogy for future targeted probes |
| NIC timestamp path-delay | Module-independent; gated on the §2 retrain-stability experiment |
- Fallback doc-mining, checked: OpenBCM's `phy8481.c` covers the copper XGPHY family only through BCM8488x — no 84891, no ECD code in the retrievable portion; the kernel's Broadcom ECD (`bcm-phy-lib`) is the BCM54xx GbE register model. Neither transfers; SDK/patent mining looks low-yield. FS delivering the ECD chapter stays the primary route.
- **Decision:** product path = the PHY's own length machinery (BCM ECD when FS delivers; `1E.C884` on the oracle); NIC timestamp path-delay = fallback, pursued only if the §2 experiment passes.
- **Decision:** product path = the PHY's own length machinery (BCM ECD, `1E.C884` on the oracle); NIC timestamp path-delay = fallback, pursued only if the §2 experiment passes. The ECD run blips the link, so length measurement is a between-runs operation, not a during-run one, unless characterization says otherwise.
## 4. Two-master I2C safety and the once-untested client assumptions