Ethernet MAC Layout Requirements

To work around the issue that JH-7110 only supports RGMII mode for Ethernet MAC connections, StarFive offers the layout recommendations depending on your need.

1,000 M Mode

If you want the 1,000 M mode support only, follow the layout design requirements below:
  • The RX/TX trace length cannot exceed 6,000 mil.
  • Match the RXD[3:0] signal group and the RX_CTL and RX_CLK signals with trace length to within 100 mil. Match the TXD[3:0] signal group and the TX_CTL and TX_CLK group trace length to within 100 mil.
  • The routing of data and clock lanes should keep a complete reference plane
Figure 1. Ethernet MAC 1,000 M Mode Only

10/100/1,000 M Mode Auto-negotiation

If you want support for 10/100/1,000 M mode auto-negotiation, be aware of the following limitations, and then you can design the layout following the requirements below.

Limitations: Only the following PHY models are supported. Additionally, you need to connect the RX_CLK of the PHY to its TX_CLK as shown by the orange lines in the following diagram.
  • YT8521DH/DC
  • YT8531DH/DC
Figure 2. 10 M/100 M/1,000 M Auto-negotiation
Layout Requirements for GMAC0
  • The trace length from TX_CLK to RX_CLK cannot exceed 500 mil.
  • The RX and TX trace length cannot exceed 4,300 mil.
  • Match the RXD[3:0] signal group and the RX_CTL and RX_CLK signals with trace length to within 100 mil.
  • Match the TXD[3:0] signal group and the TX_CTL and RX_CLK signals with trace length to within 100 mil.
  • The routing of data and clock lanes should keep a complete reference plane.
Layout Requirements for GMAC1
  • The trace length from TX_CLK to RX_CLK cannot exceed 500 mil.
  • The RX_CLK trace length cannot exceed 4,000 mil. Match the RXD[3:0] signal group and the RX_CTL and RX_CLK signals with trace length to within 100 mil.
  • The TX_CLK trace length is 2,000 mil longer than that of the RX_CLK. Match the TXD[3:0] signal group and the TX_CTL and RX_CLK signals with trace length to within 100 mil.
  • The routing of data and clock lanes should keep a complete reference plane.