Connecting Two Ethernet MDI Ports Together on One Board, No Transformers

Issue Overview

The discussion revolves around the challenge of connecting two Nvidia Jetson Nano boards directly via their Ethernet MDI ports on a custom PCB without using transformers. Users have expressed concerns about the reliability and safety of such connections, particularly in the absence of magnetic isolation.

Symptoms and Context:

• Users are seeking methods to connect two MDI ports directly, which may lead to electrical issues or signal integrity problems.
• The problem arises during the design phase of custom PCBs intended for direct board-to-board communication.
• Specific hardware mentioned includes the Nvidia Jetson Nano boards, with a focus on their Ethernet capabilities.
• The issue appears to be infrequent among users, primarily surfacing in discussions about custom designs rather than standard setups.
• The impact includes potential failure in communication between boards, which could hinder project development and functionality.

Possible Causes

• Hardware Incompatibilities or Defects: Directly connecting MDI ports without transformers may lead to electrical mismatches or damage due to voltage differences.

• Software Bugs or Conflicts: While less likely, any software configurations related to Ethernet settings could exacerbate hardware connection issues.

• Configuration Errors: Incorrect wiring or pin connections could lead to communication failures.

• Driver Issues: Incompatibilities with Ethernet drivers may affect performance if the boards are not configured correctly.

• Environmental Factors: External conditions such as temperature fluctuations or power supply inconsistencies might impact board performance.

• User Errors or Misconfigurations: Misunderstanding of MDI port connections (e.g., MDx+ to MDx- vs. crossover connections) could lead to incorrect setups.

Troubleshooting Steps, Solutions & Fixes

1. Diagnosing the Problem:

   • Verify the pinout configuration of both Nano boards to ensure correct wiring.
   • Use a multimeter to check for continuity and proper voltage levels across connections.

2. Gathering System Information:

   • Execute commands like ifconfig or ip addr in the terminal to check if the Ethernet interfaces are recognized and properly configured.

3. Isolating the Issue:

   • Test each board individually with a standard Ethernet connection to confirm that both are functional.
   • If possible, use a network hub/switch between the two boards instead of direct connection to eliminate potential electrical issues.

4. Potential Fixes and Workarounds:

   • If attempting direct connection, consider placing capacitors inline as suggested by some users; however, note that this method lacks guarantees for reliability.
   • Explore using a dedicated Ethernet switch IC that can manage connections more effectively without risking damage to the boards.

5. Documentation and Updates:

   • Regularly check Nvidia’s official documentation for updates on supported configurations and recommended practices for custom PCB designs.
   • Ensure firmware and driver updates are applied to both boards for optimal performance.

6. Best Practices:

   • Always use transformers when connecting Ethernet ports unless thoroughly tested and validated otherwise.
   • Consider designing PCBs with modularity in mind, allowing for easier troubleshooting and upgrades in the future.

Unresolved Aspects:

• There is no definitive consensus on the effectiveness of inline capacitors for this specific application. Further investigation into user experiences or expert recommendations might be necessary before proceeding with such designs.