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Sharpen MCIA open question from mlx5_ifc.h register format; drop offline-rig and instrumentation-flow framing

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flamingcow
2026-08-12 21:37:02 -07:00
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docs/nics/README.md
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@@ -22,4 +22,4 @@ Requirement weights behind the verdicts: all-packet hardware RX timestamps are n
## Architecture
- **Co-location is forced, not chosen.** SNR under load, the pre-FEC correlation, and diagnosing the module that carried the stress all require diagnostics I2C to reach the modules the traffic flows through, and module I2C is only reachable through the hosting NIC. A "diagnostics NIC" would need the modules in *its* cages, off the traffic path — structurally impossible, not merely awkward. The chassis seconds it: one usable slot.
- **The single card is the ConnectX-5.** The requirement weights flip the selection the X520 was chosen under: the 82599 stamps 1588-event frames only, txgbe is likewise PTP-only (verified in upstream `wx_ptp.c`; evaluated on paper, never owned), and mlx5 is the only driver meeting the full set — CQE-stamps every packet, one shared clock across ports, native ETHER_FLOW steering. If MCIA can't reach the BCM, product diagnostics run via the Marvell/Aquantia modules and the X520 stays an offline BCM rig ([connectx-5](connectx-5/README.md)).
- **The single card is the ConnectX-5.** The requirement weights flip the selection the X520 was chosen under: the 82599 stamps 1588-event frames only, txgbe is likewise PTP-only (verified in upstream `wx_ptp.c`; evaluated on paper, never owned), and mlx5 is the only driver meeting the full set — CQE-stamps every packet, one shared clock across ports, native ETHER_FLOW steering. If MCIA can't reach the BCM, product diagnostics run via the Marvell/Aquantia modules only ([connectx-5](connectx-5/README.md)).