# Intel X710 (i40e)

## Module I2C: 1-byte-offset only — dead end for BCM SMI

- `reg_address > 0xFF` returns AQ retval 14 (hard boundary).
- Emits at most `[dev, offset, data]` (2 payload bytes); the BCM SMI needs 3–5 byte frames in one transaction.
- MDIO interface modes don't reach the module — no PHY on the NIC MDIO pins; copper SFPs wire only I2C.
- Single-byte **writes work** (unlike the E810) — which is what makes the oracle path below possible.

## AQ oracle path (stock driver) — proved the RollBall client logic

- Transport: `/sys/kernel/debug/i40e/<pci>/command`, `send aq_cmd <flags> <opcode> 0 0 0 0 <param0> <param1> <param2> 0`, flags 0x2000.
- Opcode 0x0629 get / 0x0628 set PHY register. param0 = phy_interface | dev_addr<<8 | cmd_flags<<16 (phy_interface 2 = EXTERNAL_MODULE, dev_addr 0xA2); param1 = reg offset; param2 = value.
- Result comes back in the dmesg "AQ desc WB" line, 9th field.
- Proven on the Fibergaga, link up: per-pair SNR (PMA 1.133–1.136), PCS 3.32/3.33, the 3.E820 counter ([../../modules/fibergaga/](../../modules/fibergaga/README.md)).

## Timestamping

- Rejects `HWTSTAMP_FILTER_ALL` with -ERANGE (verified in upstream `i40e_ptp.c`) — PTP-only, so no committed-path bucketing here.
- Genuinely shared PHC across ports (one oscillator) + PTP latches: the platform for the retrain-stability experiment and the scoped-but-unbuilt PTP path-delay length fallback ([../../open-questions.md](../../open-questions.md) §2) — probes must be PTP-shaped here too.
- No EEE on i40e/X710.