cabletest/docs/open-questions.md

# Open questions

The genuinely open, thinking-worthy problems — nothing here is resolved. Analyses and settled facts live in the device docs; each entry points at the doc that holds its detail. Read `state.md` first for placement context.

## 1. Can ConnectX-5 MCIA reach the BCM? (decide on arrival)

The decisive unknown for product diagnostics coverage ([nics/connectx-5/](nics/connectx-5/README.md)):

- Does firmware MCIA accept **arbitrary I2C device addresses**? The BCM bridge sits at 0x56; kernel paths only ever use 0x50/0x51.
- Can the BCM SMI **read data phase** (raw 2-byte read, no offset write) be framed through MCIA's offset model?
- If no to either: product diagnostics via the Marvell/Aquantia modules only, X520 kept as an offline BCM rig.

## 2. ECD run disturbance

The BCM ECD run blips the link (PMA 1.1 latch-low catches a drop even with the break-link bit clear). Until the disturbance is characterized, length measurement is a between-runs operation, not a during-run one ([modules/fs/](modules/fs/README.md)).

## 3. Pre-FEC correlation run

The register question is answered (post-FEC vs corrected-by-iteration histogram located); the graded-noise correlation run that verifies the expected ordering has not happened. Design and instrument: [modules/fibergaga/](modules/fibergaga/README.md).

## 4. Wiitek VCT — pursue or leave dead?

No confirmed-safe path exists (every candidate lands in the µC danger window). The open decision is whether the capability is worth the NDA route or a sacrificial unit — the product doesn't need it for length ([modules/wiitek/](modules/wiitek/README.md), [modules/README.md](modules/README.md)).