SDAA081 September   2025 DP83825I

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Troubleshooting the Application
    1. 2.1 Schematic Checklist
    2. 2.2 Device Health Checks
      1. 2.2.1 Voltage Checks
      2. 2.2.2 Probe the RESET_N Signal
      3. 2.2.3 Probe RBIAS
      4. 2.2.4 Probe the XI Clock
      5. 2.2.5 Probe the Strap Pins During Initialization
      6. 2.2.6 Probe the Serial Management Interface (MDC, MDIO)
        1. 2.2.6.1 Read and Check Register Values
    3. 2.3 MDI Health Checks
      1. 2.3.1 Magnetics
      2. 2.3.2 Probe the MDI Signals
      3. 2.3.3 Check the Link Quality
      4. 2.3.4 Compliance
    4. 2.4 RMII Health Check
    5. 2.5 Loopback and PRBS
      1. 2.5.1 Loopback Modes
      2. 2.5.2 Transmitting and Receiving Packets with the MAC
      3. 2.5.3 Transmitting and Receiving Packets with BIST
  6. 3Summary
  7. 4References

2.5.2 Transmitting and Receiving Packets with the MAC

If generating and checking packets with the MAC is possible, and the PHY has a working link partner with reverse loopback capability, verify the full data path as follows:

  1. Power and connect the PHY to the MAC and a working link partner.
  2. Enable reverse loopback on the link partner.
  3. Transmit test packets from the MAC to the PHY.
  4. Verify the MAC receives the same test packets.

If the MAC receives the same test packets transmitted without issue, the full MAC → PHY → MDI data path is valid. If this test does not pass, perform MII loopback to isolate the issue along the data path:

  1. Power and connect the PHY to the MAC.
  2. Enable MII loopback on the PHY.
  3. Transmit test packets from the MAC to the PHY.
  4. Verify the MAC receives the same test packets.

If the MAC receives the same test packets, the MAC → PHY data path is valid, and the issue has been isolated to the MDI data path. If this test does not pass, the issue is likely on the MAC interface. To verify the MAC interface, refer to the Section 2.4 of this application note. To verify the PHY internal data path, perform the above procedure using analog loopback mode.