Does ConnectX-7 (MCX755106AC-HEAT) dual-port QSFP NIC supports RX BIST lock?

Infrastructure & Networking Adapters and Cables Ethernet Adapter Cards
1

Hello,

I am using ConnectX-7 (MCX755106AC-HEAT) dual-port QSFP NIC connected to DUT using QSFP DAC cable.

Able to get RX BIST lock in below case,

Getting BIST lock at DUT when NIC TX sending PRBS31 to DUT RX

However, when sending PRBS31 from DUT TX → NIC RX, unable to get RX BIST lock.

Below are the Queries:

  1. Please suggest steps to get BIST lock at NIC side where external DUT is sending BIST pattern. (Our DUT is continuously sending PRBS31 pattern and there is no gray coding involved)

  2. Do we need to do gray code settings at NIC side. If yes, please let us know how we can do.

Thank you

2

Hello,

The most likely causes of lock failure can be:

  • Test mode not enabled on NIC RX
  • --rx_rate doesn’t exactly match DUT TX lane rate
  • Gray coding mismatch (PAM4 only)
  • Lane polarity inversion

To get RX BIST lock on CX7, you should:

  1. mst start
  2. bring port down (required on CX7 before enabling test mode): mlxlink -d -p -a DN
  3. enable PRBS test mode matching your DUTs TX settings: mlxlink -d -p --test_mode EN --rx_prbs PRBS31 --rx_rate <lane_rate>
  4. run: mlxlink -d -p --test_mode TU
  5. Check lock: mlxlink -d <dev> -p <port> -c → look for PRBS Lock: Yes
  6. If still doesn’t lock, try adding the flag: --invert_rx_polarity
  7. Disable test mode when done: mlxlink -d -p --test_mode DS

As for gray coding, it’s only applicable for PAM4 speeds (50G+ per lane). Since your DUT sends PRBS31 without gray coding, try to add: --rx_modulation PAM4_NO_GRAY.

If there are still any issues , please feel free to open a support case with Enterprise Support and it will be handled based on entitlement.

Thanks,

Jonathan.