SNLA443 December   2023 DP83869HM

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1DP83869 Application Overview
  5. 2Troubleshooting the Application
    1. 2.1 Configuring Correct Operational Mode
    2. 2.2 Schematic and Layout Checklist
    3. 2.3 Component Checklist
    4. 2.4 Peripheral Pin Checks
      1. 2.4.1 Power Supplies
      2. 2.4.2 RBIAS Voltage and Resistance
      3. 2.4.3 Probe the XI Clock
      4. 2.4.4 Probe the RESET_N Signal
      5. 2.4.5 Probe the Strap Pins During Initialization
      6. 2.4.6 Probe the Serial Management Interface Signals (MDC, MDIO)
      7. 2.4.7 Probe the MDI Signals
    5. 2.5 Built-In Self Test with Various Loopback Modes
    6. 2.6 Debugging MAC Interface
      1. 2.6.1 RGMII
      2. 2.6.2 SGMII
  6. 3Operational Mode Clarification
    1. 3.1 Bridge Modes
    2. 3.2 Fiber Configuration
      1. 3.2.1 Fiber Registers
  7. 4Tools and References
    1. 4.1 DP83869HM Register Access
    2. 4.2 Extended Register Access
      1. 4.2.1 Read (No Post Increment) Operation
      2. 4.2.2 Write (No Post Increment) Operation
    3. 4.3 Software and Driver Debug on Linux
      1. 4.3.1 Common Terminal Outputs
  8. 5Summary
  9. 6References

3.2.1 Fiber Registers

DP83869HM has several fiber related registers, this section is intended to summarize a few of their functionalities and show how to debug. Link status can always be checked in register 0x01, but register 0xC01 checks Fiber link.

Table 3-2 Register 0xC01 Behavior
Mode Register 0xC01 behavior
RGMII to Fiber Behaves the same as register 0x01, meaning there is no added benefit of reading register 0xC01
Media Convertor Mode

Case 1: Copper link is down but Fiber link is up

Register 0x01 indicates link is down (copper side), but register 0xC01 shows link is up (fiber side). This is helpful for being able to debug which cable is at fault.

Case 2: Copper link is up but Fiber link is down

Register 0x01 indicates link is down. If register 0xC01 says link is down, register 0x01 is also down.

Case 2 in Table 3-2 does not give full confidence in which link is down. The Fiber Interrupt Status Register (0xC19) can be used to isolate where the fault is. In Case 2, 0xC19[9] (Fiber Far End Fault) and 0xC19[4] (Link Status Change) can flag. In Case 1, only 0xC19[4] can flag.